| 1. |
- Arvola, Marie
(författare)
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Immunological aspects of maternal-foetal interactions in mice
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mammalian pregnancy is an immunological paradox. The foetus, which expresses both paternal and maternal cell-surface molecules, has to be protected from rejection by the maternal immune system. At the same time, the mother has to have an efficient immune defence and must provide her offspring with antibodies.The first part of this thesis investigates some of the mechanisms involved in the foetal avoidance of maternal rejection reactions. Placental absence of MHC class II expression, as well as a bias for Th2-cytokines at the maternal-foetal interface are suggested to be important for foetal survival. The results showed that placental MHC class II expression cannot be induced in vivo. Transfections of trophoblast cells with MHC class II genes, however, resulted in detectable MHC class II cell-surface expression, indicating that a post-transcriptional block does not exist in these cells.By using IL-4- and IL-10-double deficient mice, it was shown that neither maternal nor foetal expression of these cytokines were crucial for completion of allogeneic pregnancy.In the second part of the thesis, the effect of transmission of immunoglobulin G (IgG) from the mother to the offspring was studied. It was observed that viable maternal Ig-secreting cells occasionally infiltrated the B cell-deficient offspring and remained functional for long periods. In this study "green fluorescent mice" were used as a tool. Furthermore, neonatal ingestion of wild type milk increased the survival of adoptively transferred B-lineage cells in B cell-deficient mice, suggesting that suckling of IgG-containing milk could be used to facilitate B cell-reconstitution in B cell-deficient mice. Finally, results from studies on normal mice showed that absence of maternal IgG-transmission during their neonatal development resulted in elevated serum-IgG production, as well as enhanced immune reactions upon immunisations in adult life. This showed that maternal IgG can have long-term immunoregulatory effects in the offspring.
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| 2. |
- Ericsson, Rolf
(författare)
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A Comparative Study of Head Development in Mexican Axolotl and Australian Lungfish: Cell Migration, Cell Fate and Morphogenesis
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of the vertebrate head is a complex process involving interactions between a multitude of cell types and tissues. This thesis describes the development of the cranial neural crest and of the visceral arch muscles in the head of two species. One, the Mexican axolotl (Ambystoma mexicanum), is a basal tetrapod, whereas the other, the Australian lungfish (Neoceratodus forsteri), belongs to the Dipnoi, the extant sister group of the Tetrapoda. The migration of neural crest cells, which form most of the bones and connective tissues in the head, and the morphogenesis of the jaw, was determined in the Mexican axolotl. It was shown that both the upper and lower jaws form from ventral condensations of neural crest cells in the mandibular arch. The dorsal condensation, earlier considered to give rise to the upper jaw, was shown to form the trabecula cranii.The normal spatio-temporal development of visceral arch muscles was investigated in both the Mexican axolotl and the Australian lungfish. In axolotl, the muscles tended to start forming almost simultaneously in all visceral arches at their future origins and extend towards their future insertions at the onset of muscle fibre formation. In lungfish, fibres formed simultaneously throughout most of each muscle anlage in the first and second visceral arch, but were delayed in the branchial arches. The anlagen were first observed at their future insertion, from which they developed towards future origins. To test the ability of neural crest cells to pattern the visceral arch muscles, migrating crest cells were extirpated from axolotl embryos, which resulted in a wide range of muscle malformations. In most cases, the muscles appeared in the right position but were small and extended in abnormal directions. This shows that neural crest cells are responsible not for the position of the muscles but for their correct anatomical pattern. Fate mapping showed that connective tissue surrounding myofibers is, at least partly, neural crest derived.In conclusion, the work presented in this thesis shows that although early development may map out the patterns of later development, the differences between axolotl and lungfish head development are not seen until during morphogenesis. Further investigation of morphogenesis is needed to explain the great variation of head morphology seen in vertebrates today.
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| 3. |
- Holmgren, Claes
(författare)
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Epigenetic Regulation of the H19 Chromatin Insulator in Development and Disease
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The coordinated regulation of gene expression must be tightly controlled for normal development to occur. In mammals, this issue is further complicated by the requirement of both the maternal and paternal genomes for normal development, reflecting the fact that a subset of genes are monoallelically expressed depending on parental inheritance, a phenomenon known as genomic imprinting. The imprinted H19 and Igf2 genes are often considered as paradigms of genomic imprinting, since their monoallelic expression patterns are coordinated via a short stretch of sequence upstream of H19, known as the imprinting control region (ICR). This region is differentially methylated, with specific CpG methylation on the paternal allele. It is shown here that the ICR harbours several maternal-specific hypersensitive sites, located in linker regions between positioned nucleosomes. Furthermore, this region functions as an orientation-dependent insulator, that binds the chromatin insulator factor CTCF. The hypothesis that the methylation status of the ICR dictates the activity of the Igf2 gene 90 kb further upstream was confirmed by the demonstration that the insulator function is lost when the ICR is CpG methylated. The ICR has previously been shown to act as a silencer when positioned in a promotor-proximal position. The cause of this silencing was shown to be distance-dependent, suggesting that the silencing features of the ICR depend on a chromatin conformation that renders adjacent sequences inaccessible to the RNA polymerase. These data issue a cautionary note with respect to the interpretation of silencer functions. In several forms of cancer, the normally silent maternal IGF2 gene is expressed, possibly as a result of loss of insulator function at the ICR. The utilisation of CTCF target-sites was analysed in different tumours, and was shown to be highly variable. Methylation analysis showed that potential loss of insulator function and gain of methylation at the maternal ICR did not always correlate with biallelic expression of IGF2. Further investigations uncovered a novel mechanism, in which the activation of the IGF2 promoter was independent of insulator function in some cancers. This thesis shows that the regulation of the imprinted state of Igf2 depends on the formation of an epigenetically regulated chromatin insulator, and that the loss of IGF2 imprinting in human cancer can be attributed to several mechanisms, including a novel mechanism that neutralises chromatin insulator function.
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| 4. |
- Liu, Liang, 1972-
(författare)
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Epigenetic Control of Mammalian Development : Studies on an imprinting control region
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A subset of autosomal genes is preferentially or exclusively expressed from one of the parental alleles. This phenomenon, termed genomic imprinting, is highlighted by the neighboring Igf2 and H19 genes, which are monoallelically expressed on opposite parental chromosomes. These features are governed by a 2.2 kb differentially methylated domain, hereafter termed imprinting control region (ICR) in the 5'-flank of the H19 gene. It was shown that the H19 ICR displays unique chromatin conformation features with nuclease hypersensitive sites in linker elements flanked by positioned nucleosomes on the maternally derived allele. Moreover, it was demonstrated that the unmethylated ICR functions as a unidirectional chromatin insulator, which involves the chromatin insulator protein CTCF.The methylated and unmethylated states of the paternal and maternal H19 ICR alleles are known to be stably propagated in the soma throughout development. During in vitro organogenesis, however, the stability of the H19 ICR was demonstrated to be disturbed due to presence of environmental cues. The methylation plasticity of the H19 ICR was nevertheless tolerated without affecting the imprinted status of either Igf2 or H19 genes. It was also observed that some human cancer cell lines possess strong de novo methylation activities. Following transfection of an episomal construct, which contains the H19 miningene with the core H19 ICR and its human counterpart, the H19 reporter gene became rapidly do novo methylated and eventually silenced in choriocarcinoma cells (JEG-3), but not in heptoma cells (HEP3B). Although the H19 ICR was initially protected from being methylated by JEG3 cells, progressive waves of de novo methylation generated a heavily methylated H19 ICR in later passages, with concomitant loss of its insulator function. It is generally accepted that parental marks undergo erasure and reestablishment during gametogenesis. It was shown that CTCF and its paralogue, BORIS, are expressed in reciprocal patterns during adult male germline development. By means of laser-dissection and bisulfite genomic sequencing, it was observed that de novo methylation of CTCF target sites occurred in BORIS-expressing spermatocytes that exhibit repression of CTCF gene. It was also shown, by chromatin immunopurification analyses of adult mouse testes, that CTCF and BORIS were associated with H19 ICR. A model is proposed to explain the acquisition of differential methylation marks in molecular terms.
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| 5. |
- Mörck, Catarina, 1972, et al.
(författare)
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pha-2 encodes the C. elegans ortholog of the homeodomain protein HEX and is required for the formation of the pharyngeal isthmus.
- 2004
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Ingår i: Developmental Biology. - : Elsevier BV. - 0012-1606. ; 272:2, s. 403-418
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Tidskriftsartikel (refereegranskat)abstract
- The pha-2 mutant was isolated in 1993 by Leon Avery in a screen for worms with visible defects in pharyngeal feeding behavior. In pha-2 mutant worms, the pharyngeal isthmus is abnormally thick and short and, in contrast to wild-type worms, harbors several cell nuclei. We show here that pha-2 encodes a homeodomain protein and is homologous to the vertebrate homeobox gene, Hex (also known as Prh). Consistent with a function in pharyngeal development, the pha-2 gene is expressed in the pharyngeal primordium of Caenorhabditis elegans embryos, particularly in pm5 cells that form the bulk of the isthmus. We show that in the pha-2 mutant there is a failure of the pm5 cells to elongate anteriorly while keeping their nuclei within the nascent posterior bulb to form the isthmus during the 3-fold embryonic stage. We also present evidence that pha-2 regulates itself positively in pm5 cells, that it is a downstream target of the forkhead gene pha-4, and that it may also act in the isthmus as an inhibitor of the ceh-22 gene, an Nkx2.5 homolog. Finally, we have begun characterizing the regulation of the pha-2 gene and find that intronic sequences are essential for the complete pha-2 expression profile. The present report is the first to examine the expression and function of an invertebrate Hex homolog, that is, the C. elegans pha-2 gene.
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| 6. |
- Smith, Nick G.C., et al.
(författare)
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Evidence for turnover of functional noncoding DNA in mammalian genome evolution
- 2004
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Ingår i: Genomics. - : Elsevier BV. - 0888-7543 .- 1089-8646. ; 84:5, s. 806-813
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Tidskriftsartikel (refereegranskat)abstract
- The vast majority of the mammalian genome does not code for proteins, and a fundamental question in genomics is: What proportion of the noncoding mammalian genome is functional? Most attempts to address this issue use sequence comparisons between highly diverged mammals such as human and mouse to identify conservation due to negative selection. But such comparisons will underestimate the true proportion of functional noncoding DNA if there is turnover, if patterns of negative selection change over time. Here we test whether the inferred level of negative selection differs between different pairwise species comparisons. Using a multiple alignment of more than a megabase of contiguous sequence from eight mammalian species, we find a strong negative relationship between inferred levels of negative selection and pairwise divergence using 21 pairwise comparisons. This result suggests that there is a high rate of turnover of functional noncoding elements in the mammalian genome, so measures of functional constraint based on human–mouse comparisons may seriously underestimate the true value.
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| 7. |
- Ullerås, Erik
(författare)
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Gene expression and its physiological control in disease and development : Studies on the human PDGF-B gene and tumour hypoxia
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Strict control of gene expression is essential during development and in response to physiological stimuli. This thesis describes the functional characterisation of the gene regulatory mechanisms controlling the expression of the potent human growth factor Platelet Derived Growth Factor B gene, in a cell type specific context and in response to low oxygen tension. In addition, analysis of hypoxia in neuroblastoma indicates a role during tumour differentiation. Initally, a promoter-specific enhancer system controlling the expression of PDGF-B was characterised in placentally derived choriocarcinoma cells. The specificity of this enhancer promoter interaction was shown to be dependent on specific sequence elements identified in both the promoter and enhancer regions. It was then shown that the activity of the PDGF-B promoter is controlled via modulation of histone acetylation status in a cell type specific manner and furthermore, that one role of its enhancer could be to regulate transcription via alterations in acetylation status at the promoter. PDGF-B expression was then shown to be controlled by hypoxia in a biphasic manner in bladder carcinoma cells. An initial induction was followed by repression of transcription following chronic hypoxia. The biphasic response was shown to be dependent on glucose levels and uniquely amongst hypoxia regulated genes studied so far, PDGF-B expression was shown to be repressed by low glucose. Finally, detailed in vivo and in vitro analysis revealed that the major form of differentiation in childhood neuroblastoma is towards chromaffin-like rather than ganglionic lineages. This type of differentiation did not correlate with disease progression but was suggested to be dependent on tumour hypoxia, since chromaffin differentiation markers co-localised with markers of tumour hypoxia in both clinical samples and xenogenic tumours. In conclusion, the work presented in this thesis has identified several novel, highly specific gene regulatory mechanisms that are involved in development, the response to physiological stimuli and in disease progression.
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| 8. |
- Øverli, Øyvind
(författare)
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Behavioural and Neuroendocrine Effects of Stress in Salmonid Fish
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stress can affect several behavioural patterns, such as food intake and the general activity level of an animal. The central monoamine neurotransmitters serotonin, dopamine, and norepinephrine are important in the mediation of both behavioural and neuroendocrine stress effects. This thesis describes studies of two salmonid fish model systems: Fish that become socially dominant or subordinate when reared in pairs, and rainbow trout (Oncorhynchus mykiss) genetically selected for high (HR) and low (LR) stress responsiveness, in terms of stress induced cortisol release. Socially subordinate individuals are often subject to chronic stress, and it was found that plasma cortisol and brain monoaminergic activity rapidly increased in subordinate fish during the initial 24 h period following fights for social dominance in pairs of rainbow trout. In pairs of Arctic char (Salvelinus alpinus), subordinate individuals were characterised by an inhibition of food intake and aggression, and low spontaneous locomotion. Appetite inhibition in subordinate fish was reversed by subsequent rearing in isolation, and this effect was probably related to a concomitant decrease in brain serotonergic activity. Furthermore, differential stress responsiveness in HR and LR rainbow trout was associated with differences in behaviour, as well as changes in brain monoaminergic activity. HR fish displayed higher locomotor activity when challenged by a conspecific intruder. This response was probably related to a larger stress induced activation of brain dopaminergic systems in these fish. Finally it was shown that the steroid 'stress-hormone' cortisol has dose- and context-dependent behavioural effects in fish, as has been described in mammals. Specifically, short- term cortisol treatment elevated the behavioural response to a territorial intruder, while long-term treatment, like chronic stress, had the opposite effect, inhibiting locomotor activity and aggression. It is concluded that the signalling systems involved in behavioural and neuroendocrine control during stress display extensive similarities between teleost fishes and mammals.
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| 9. |
- Savolainen, Peter, et al.
(författare)
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mtDNA tandem repeats in domestic dogs and wolves : Mutation mechanism studied by analysis of the sequence of imperfect repeats
- 2000
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Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 17:4, s. 474-488
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Tidskriftsartikel (refereegranskat)abstract
- The mitochondrial (mt) DNA control region (CR) of dogs and wolves contains an array of imperfect 10 bp tandem repeats. This region was studied for 14 domestic dogs representing the four major phylogenetic groups of nonrepetitive CR and for 5 wolves. Three repeat types were found among these individuals, distributed so that different sequences of the repeat types were formed in different molecules. This enabled a detailed study of the arrays and of the mutation events that they undergo. Extensive heteroplasmy was observed in all individuals; 85 different array types were found in one individual, and the total number of types was estimated at 384. Among unrelated individuals, no identical molecules were found, indicating a high rate of evolution of the region. By performing a pedigree analysis, array types which had been inherited from mother to offspring and array types which were the result of somatic mutations, respectively, could be identified, showing that about 20% of the molecules within an individual had somatic mutations. By direct pairwise comparison of the mutated and the original array types, the physiognomy of the inserted or deleted elements (indels) and the approximate positions of the mutations could be determined. All mutations could be explained by replication slippage or point mutations. The majority of the indels were 1-5 repeats long, but deletions of up to 17 repeats were found. Mutations were found in all parts of the arrays, but at a higher frequency in the 5' end. Furthermore, the inherited array types within the mother-offspring pair were aligned and compared so that germ line mutations could be studied. The pattern of the germ line mutations was approximately the same as that of the somatic mutations.
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| 10. |
- Eriksson, Joakim
(författare)
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Evolution and Development of the Onychophoran Head and Nervous System
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Onychophorans are closely allied to the arthropods and possess a body organisation more similar to Middle Cambrian fossils than to recent arthropods. This means that onychophorans in some respects can be regarded as a model for the last common ancestor to both the Arthropoda and the Onychophora. This thesis mainly deals with the morphology of the head region of the Onychophora, but developmental investigations of the expression of a key regulatory gene, engrailed, are also carried out. The innervation of the head was found to differ from that reported in earlier investigations. The nerves that support the mouth were found to originate from three different regions of the brain. That innervation pattern suggests that present day onychophorans with a ventrally placed mouth, have evolved from an ancestor with a terminal mouth. Furthermore it was confirmed that the onychophoran structure with the unfortunately chosen term labrum is not homologous to the structure in arthropods that bears this name. Instead it is a muscular outgrowth from the pharynx. The embryological investigations gave further support for an ancestral and terminal mouth. The two most anterior oral lips are first located on the dorso-frontal side of the head, and later migrate to their final position at the ventral side. This phenomenon also explains their somewhat unexpected innervation from the dorsum. It was also established that the eye originates at a position posterior to the antenna. This is reversed compared to the condition in arthropods, were the eye is innervated from the protocerebrum and the first antenna from the dutocerebrum, and implies that the eye and antenna are not serially homologous between the two groups. A structure in the onychophoran head that has gained little attention is the hypocerebral organ, also termed infracerebral organ. It has been suggested as a corpora allata analog by earlier workers. Its ultrastructure was investigated, and great similarities to the corpora allata of the stick insect Carausius morosus were found. However, the lack of innervation of the hypocerebral organ of Onychophora poses a problem since the corpora allata of insects is controlled by nerves. Instead, cellular strands were found that connected the hypocerebral organ with the brain, and it is possible that these strands act as an alternative communication. The expression pattern of the segment polarity gene engrailed was found to be different from that reported in an earlier account of onychophorans. Engrailed was expressed in a subset of developing neurons in the brain anlage and in the ectoderm and mesoderm of the limb buds. The engrailed positive cells in the brain anlage were located in the area were the first commissure will form. This indicates that engrailed might have a function in axon guidance, as has been reported in other organisms. Later embryonic stages showed expression in the neuropile of the brain. There were no indications of this gene acting in determination of segment polarity. This suggests that there may be at least two copies of engrailed in onychophorans.
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| 11. |
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| 12. |
- Alsmark, Cecilia
(författare)
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Comparative Genomics of Obligate and Facultative Intracellular Parasites
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The α-proteobacteria Rickettsia prowazekii and Bartonella henselae are the causative agents of epidemic typhus and cat scratch disease respectively. Whereas R. prowazekii is an obligate intracellular parasite, B. henselae can live and proliferate both outside and inside the eukaryotic host cell. Besides the obvious medical interest to identify the complete gene set of two human pathogens, their genome sequences are also important for the study of evolutionary processes. Both R. prowazekii and B. henselae have small genomes, but their last common ancestor of these two bacteria was most likely a free-living organism with a substantially larger genome.The aim of this thesis is to compare the complete genomes of R. prowazekii and B. henselae and to decipher the evolutionary processes leading to the adaptation to an intracellular lifestyle. The working hypothesis was that the facultative intracellular B. henselae is an intermediate between a free living bacteria and the obligate R. prowazekii, which is corroborated. B. henselae has a broader biosynthetic repertoire than R. prowazekii, including the presence of genes for glycolysis and de novo biosynthesis of purines and pyrimidines. However, both bacteria have reduced gene sets for biosynthesis of amino acids and cofactors compared to free-living bacteria.Comparisons of gene order in bacteria reveal that several operons are well conserved between distantly related species. The genome sequences of R. prowazekii and B. henselae show that many of the operons that are usually conserved, are broken and rearranged in these species. One of the mechanisms of reductive evolution include intra-chromosomal recombination between repeated loci. This process expels one of the repeats and cause rearrangements in the gene order of the flanking regions. While the R. prowazekii genome almost completely lack repeated sequences, the B. henselae genome is rich in repeats. These repeats are, however, most often located within regions associated with pathogenicity islands. The higher number of scrambled operons, and the lower number of repeats, in R. prowazekii compared to B. henselae imply that the reductive process has gone further in the former species.
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| 13. |
- Amiri, Haleh, 1966-
(författare)
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Patterns and Processes of Molecular Evolution in Rickettsia
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Species of the genus Rickettsia are obligate intracellular parasites of the a-proteobacterial subdivision. It has been suggested that obligate intracellular bacteria have evolved from free-living bacteria with much larger genome sizes. Transitions to intracellular growth habitats are normally associated with radical genomic alterations, particularly genome rearrangements and gene losses.This thesis presents a comparative study of evolutionary processes such as gene rearrangements, deletions and duplications in a variety of Rickettsia species. The results show that early intrachromosomal recombination events mediated by duplicated genes and short repeats have resulted in deletions as well as rearrangements. For example, an exceptional organization of the elongation factor genes was found in all species examined, suggesting that this rearrangement event occurred at the early stage of the evolution of Rickettsia. Likewise, it was found that a repetitive element, the so-called Rickettsia Palindromic Element (RPE) flourished prior to species divergence in Rickettsia. Finally, a phylogenetic analysis shows that the duplication events that gave rise to the five genes encoding ATP/ADP transporters occurred long before the divergence of the two major groups of Rickettsia. Taken together, this suggests that Rickettsia have been intracellular parasites for an extensive period of time.A detailed analysis of the patterns of nucleotide changes in genes and intergenic regions among the different species provides evidence for a gradual accumulation of short deletions. This suggests that different distributions of genes and repeated sequences in modern Rickettsia species reflect species-specific differences in rates of deterioration rather than variation in rates of intra-genomic sequence proliferation.
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| 14. |
- Andersson, Måns S.
(författare)
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Physiological trade-offs in reproduction and condition dependence of a secondary sexual trait
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines parental condition, how it is traded off against reproduction and how it is displayed in a secondary sexual trait. The studies were performed on nest-box breeding collared flycatchers Ficedula albicollis on the island of Gotland, in the Baltic Sea. Early breeding and high fitness were found to be associated with high levels of glycosylated haemoglobin possibly governed by migratory exertion and infectious disease. In order to test if immune function is expressed in secondary sexual traits and how it is traded off against reproductive effort a series of experiments were performed, in which birds were challenged with an antigen, via a vaccine containing neutralised paramyxovirus. The forehead patch of the male collared flycatcher serves as a badge of status and is under sexual selection. Good condition, as reflected in strong immune response and low levels of blood parasites was found to be associated with bigger patch size. Patch size was also found to vary in size within the same breeding season in a pattern predictable from immune response data. Immune response, in itself, was found to be costly in terms of reduced survival, confirming that trade-offs involving suppression of immune response may increase fitness. Mating effort was found to be traded off against immune function and moult. Experimental brood size manipulations revealed a trade-off females between number of offspring and immune function. Thus I suggest a set of parameters useful for condition estimation. I also show that immune response is costly and, second, that pathogen resistance probably plays an important role in the shaping of secondary sexual traits and life-history decisions.
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| 15. |
- Bahrami, Fariba
(författare)
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Methylsulphonyl-chlorobenzenes and the olfactory system : Comparative toxicity of the 2,5- and 2,6-dichlorinated isomers in mice
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methyl sulphone metabolites of chlorinated aryl hydrocarbons are persistentenvironmental pollutants that can bioaccumulate in animals and humans. Little is known about the toxicological effects of these metabolites and this thesis is an attempt to increase this limited knowledge. Tissue-binding, toxicity and neuro-behavioural effects of methylsulphonyl-2,6dichlorobenzene [2,6-(diCl-MeSO2-B)] and methylsulphonyl-2,5-dichlorobenzene [2,5-(diCl-MeSO2-B)] were examined on mice.Both substances resulted in a strong uptake in the olfactory mucosa (OM). Only 2,6-(diCl-MeSO2-B) induced toxicity in the OM, originating from a primary lesion in the Bowman's glands (BG). An in situ CYP-catalysed activation of 2,6-(diCl-MeSO2-B) seems to occur in the BG giving rise to reactive intermediates which either conjugate with glutathione or induce local toxicity. Subsequent secondary lesions in the OM include: severe degenerationof the neuroepithelium, fibrosis, ossification and polyposis. These effects resulted from a single ip dose and were permanent. Long lasting induction of GFAP in the olfactory bulb (OB) and behavioural deficits were also observed and considered to be caused by damaged olfactory neurons and/or metabolites translocated to the OB. Although the OM was more damaged in male mice, acquisition deficits occurred only in female mice.2,5-(diCl-MeSO2-B) did not induce OM toxicity, GFAP or learning deficits in either sex. However, observed motor activity responses indicate that, although 2,5-(diCl-MeSO2-B) is not olfacto-toxic, it is neuro-toxic.1,3-Dichloro-, 1,4-dichloro- or 1,2,3-trichloro-benzene did not induce damage in the OM indicating that an electron withdrawing substituent in the primary position and 2,6-positioned chlorine atoms is a structural requirement for OM toxicity. Persistent, dose-, time-, tissue- and sex-dependent effects on the olfactory system induced by 2,6-(diCl-MeS2-B) together with the lack of lesions in the OM or brain by 2,5-(diCl-MeSO2-B), makes this chemical pair a reliable and versatile tool for olfactory research.
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| 16. |
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| 17. |
- Bekele, Tesfaye
(författare)
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Plant Population Dynamics of Dodonaea angustifolia and Olea europaea ssp. cuspidata in Dry Afromontane Forests of Ethiopia
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human disturbance has led to excessive deforestation and to a very limited forest cover in the Afromontane zone of Ethiopia, which forms a large part of the country. Thus urgent conservation measures are required to ameliorate the situation. Understanding the natural regeneration processes and the dynamics of plant populations of tree and shrub species has a practical application in the restoration of these habitats.The present study focuses on the population dynamics and regeneration of an early successional shrub Dodonaea angustifolia and a late successional tree Olea europaea ssp. cuspidata in southern Wello, Ethiopia. Population structure and dynamics, regeneration and seed banks in dry Afromontane habitats were considered.For both species, three population structure patterns were identified: 1) high density, reversed J-shape structure with many seedlings and few large individuals, 2) lower density, unimodal structure with higher proportions of plants of intermidiate size, 3) high density with higher proportions of large plants , in some cases bimodal with small and large individuals. Vegetation type and protection time were found to have a significant effect on the population structure of both species. Dodonaea can establish itself on degraded land, once the disturbance has ceasedProjection matrix analysis on observations from permanent plots in Dodonaea populations in protected and unprotected sites resulted in one declining population, and one increasing in the protected site and declining populations at the unprotected site. The overall projected growth rate in Dodonaea calculated from a pooled matrix indicated positive population growth. The factors influencing the population growth, recruitment and survival are discussed.The persistence of Olea populations seems to depend on the more stable environmental conditions in later successional stages of forest vegetation. There are possibilities of natural regeneration of Olea if regenerating individuals still occur in the area. Rainfall seasonality is a dominant factor in regulating establishment, recruitment, survival and growth, particularly during the seedling stage. Moreover, shade and herbivory are factors that need consideration. Since Olea grows better under shade than in the open sun, successful regeneration for this species relies on shade from other plants and on protection from grazing, at least during the seedling stage.Most of the species that germinated from the seed banks were herbs and grasses with very few shrub and tree species. There was low correspondence between species composition of the seed banks and that of the standing vegetation.Spatial and temporal variation in demographic parameters among populations of Dodonaea and Olea can be attributed to human and environmental influence. Under protection, both Dodonaea and Olea seem to have a possibility to regenerate naturally. Further research should consider factors mentioned in detailed investigations of other dominant Afromontane forest species.
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| 18. |
- Berg, Lars M.
(författare)
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Genetic Disequilibria and the Interpretation of Population Genetic Structure in Daphnia
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the processes that shape the spatial distribution of genetic variation within species is central to the evolutionary study of diversification and demography. Neutral genetic variation reflects past demographic events as well as current demographic characteristics of populations, and the correct interpretation of genetic data requires that the relative impact of these forces can be identified. Details of breeding systems can affect the genetic structure through effects on effective migration rate or on effective population size. Restrictions in recombination rate lead to associations between neutral marker genes and genes under natural selection. Although the effects on genetic structure can be substantial, the process will often be difficult to tell apart from stochastic effects of history or genetic drift, which may suggest erroneous conclusions about demography.In cyclically parthenogenetic freshwater invertebrates, which alternate between sexual and asexual reproduction, demographic fluctuations and reliance on diapausing eggs for dispersal enhances neutral genetic differentiation as well as effects of selection on associated genes. Although genetic founder effects are expected to be profound and long-lasting in these species, genetic hitch-hiking may reduce initial strong differentiation rapidly if better adapted genes are introduced by mutation or immigration. Fluctuating environmental conditions have been suggested to generate rapid shifts in the frequencies of clones during the asexual phase. In the presence of egg banks resting in sediments, genetic diversity is stabilised and the importance of migration for differentiation is reduced.Studies of unstable and young populations of cyclically parthenogenetic Daphnia pulex showed substantial variation for important fitness traits, within as well as between populations, despite hypothesised recent founder effects. Neutral markers indicated genetic equilibrium, but changes in clonal composition during asexuality disrupted the genetic structure in a manner compatible with local adaptation and exclusion of immigrants. This illustrates that the forces affecting sexual progeny may be markedly different from those shaping the structure among asexual individuals.
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| 19. |
- Brohede, Jesper, 1972-
(författare)
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Rates and Patterns of Mutation in Microsatellite DNA
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sequence comparisons of orthologous microsatellite loci in cattle and sheep revealed that the substitution rate in microsatellite flanking sequences does not differ from the rate in presumably neutrally evolving intron sequences. This suggests that microsatellites are generally located in regions that are not subjected to selection. Interestingly, a propensity for substitutions to occur in the border region between flanking and repeat sequence was found.Pedigree analysis of large numbers of barn swallows revealed extremely high mutation frequencies for the tetranucleotide HrU6 and pentanucleotide HrU10 repeat loci. A detailed analysis showed that both the rate and the pattern of mutation differed significantly between the two loci.Further analysis of HrU6 and HrU10 mutations, as well as mutation data for another hypermutable locus (HrU9) in barn swallows, revealed that mutations were more likely to arise in some families than others. This was partly, but probably not only, due to an effect of allele length on mutation rate. The mutation rate was found to vary between colonies of breeding birds, but, overall, not between two different populations.Single molecule genotyping of DNA prepared from human sperm cells was used to detect mutations at the tetranucleotide repeat D21S1245. A tenfold difference in mutation rate between alleles was found. Three phylogenetically distinct allele lineages could be defined, which differed significantly in mutation rate. Unexpectedly, the mutation rate was not found to increase with male age. Microsatellites are commonly applied in a wide range of genetic contexts including linkage mapping, forensic science and population genetics. Obtaining a detailed picture of the evolution of these tandem repeats is important in order to fully understand how to interpret microsatellite data. In addition, studies of the mechanisms underlying microsatellite mutation will provide insights in the processes that shape the eukaryotic genome.This thesis demonstrates that microsatellite evolution is a highly heterogeneous process that is dependent on more factors than was previously thought. As the rate and pattern may vary between loci, caution must therefore be taken when building models to handle microsatellite data.
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| 20. |
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| 21. |
- Cross, JC, et al.
(författare)
-
Genes and development : a workshop report
- 2004
-
Ingår i: Placenta Supplement A, Trophoblast Research. - : Elsevier BV. - 0143-4004. ; 18, s. S39-S41
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Tidskriftsartikel (refereegranskat)
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| 22. |
- Dupré, Cecilia
(författare)
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Regional and local variation in plant species richness
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I examine the variation in plant species richness along gradients of productivity and disturbance in grasslands and forest habitats in southern Sweden, and I compare the documented patterns with theoretical predictions. Moreover, I evaluate the relative importance of habitat quality and habitat configuration for the occurrence of field layer species in deciduous forests. Finally, I present a new method for the determination of the regional species pool. To examine regional and local variation in plant species richness, I gathered data on species composition in plots of different size (0.001 - 1000 m2) in three vegetation types (deciduous forests, dry grasslands and coastal meadows) in four regions of southern Sweden (Öland, Gotland, Småland and Uppland). As predicted by the species pool hypothesis, differences in small-scale species richness of deciduous forests and dry grasslands were correlated with differences in the size of the regional species pool. Moreover, among plots large-scale diversity was predictive of small-scale diversity. Species diversity showed a hump-shaped relationship with productivity in forests, and was related to environmental heterogeneity and the size of the 'habitat-specific' species pool. In the two types of grassland examined, grazed sites were richer in species than abandoned sites. Moreover, both species composition and the representation of plants with different life-history characteristics differed between grazed and abandoned sites. As predicted by the intermediate disturbance hypothesis, species richness was highest at intermediate levels of grazing in coastal meadows. However, all the above patterns were scale-dependent, and not observed at all plot sizes. The occurrence of field layer species in deciduous forests was more strongly related to habitat quality (mainly soil factors) than to habitat configuration (forest area and isolation). Across species, low seed production, clonal reproduction and habitat specificity were negatively associated with isolation.
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| 23. |
- Eliapenda, Shadrack
(författare)
-
Plant ecological studies related to restoration of a degraded ecosystem in central Tanzania
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Kondoa Irangi area is among the most degraded ecosystems in Central Tanzania as a result of heavygrazing, fire, collection of fuelwood and improper cultivation practices. The restoration process of thisdegraded ecosystem through natural regeneration is slowed by the semi-arid climate of the area combinedwith poor soil nutrient status. Studies of population ecology of Acacia seyal and Brachystegia spiciformiswere conducted with and without protection against fire, grazing/browsing by animals and humandisturbance. The floristic and structural diversity of a remnant Afromontane forest was described. Inaddition, facilitation of regeneration in the study area through soil amendment, seeding and seedlingintroduction were also performed. The purpose of these studies was to obtain information that can beused for ecological restoration of the area as well as conservation of the remaining fragments of thenatural vegetation.For both Acacia seyal and Brachystegia spiciformis population densities, recruitment rates,seedling survival and population growth rates were generally higher in the protected than in theunprotected plots. The overall and stage-specific mortality rates of both species were usually higher in theunprotected than in the protected plots. The differences in vital rates between the two types ofenvironment suggest that beside climatic factors that cause temporal variation, tire, grazing and humaninfluence the plant population dynamics in the area.Soil amendments to facilitate regeneration showed that direct addition of seeds and planting ofseedling, particularly, of drought resistant species can be applied to increase recruitment and speciesdiversity and to promote regeneration. Nitrogen and other mineral deficiencies in the soil can becorrected naturally by, for example, addition of mulch and establishment of leguminous plants rather than by inorganic fertilization.In the Afromontane forest, timber species had declining populations, indicating the effect ofselective logging, while other species showed expanding or interrupted populations. A proposal toconserve this forest under a community-based forest conservation scheme is put forward. Based on thesestudies it can be concluded that the restoration of this degraded ecosystem is possible if disturbance doesnot exceed the present levels.
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| 24. |
- Enarsson, Mia, 1974-
(författare)
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Roles of PDGF for Neural Stem Cells
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stem cells are endowed with unique qualities: they can both self-renew and give rise to new mature cell types. Central nervous system (CNS) stem cells can give rise to neurons and glia. What factors regulate stem cell fate decisions? Identifying signals that are involved in the regulation of CNS stem cell proliferation, survival, differentiation and migration is fundamental to the understanding of CNS development. In addition, this knowledge hopefully will contribute to more efficient therapies of CNS damages and diseases.The focus of this thesis was to investigate mechanisms of CNS stem cell proliferation and differentiation. We have studied the role for platelet-derived growth factor (PDGF) in these cellular events both in vitro and in vivo. Previous reports have shown that PDGF are implicated in brain tumorigenesis and also supports neuronal differentiation of CNS stem cells. We have found that PDGF promotes survival and proliferation of immature neurons, thereby supporting neuronal differentiation. The intracellular Ras/ERK signaling pathway probably mediates the mitogenic activity of PDGF. In contrast, neuronal differentiation is not dependent on the Ras/ERK pathway. A genetic expression profile of stem cells during their differentiation was obtained. This microarray analysis suggests that PDGF-treated stem cells are at an intermediate stage between proliferation and differentiation. Furthermore, we generated transgenic mice that overexpress Pdgf-b in neural stem cells. Preliminary data indicate no signs of enhanced proliferation of immature neurons. Instead, increased apoptosis was detected in the developing striatum.The results presented in this thesis show how CNS stem cells are regulated by PDGF. PDGFs are widely expressed in the developing CNS and also in some brain tumors, which are thought to arise from CNS stem cells. Thus, this knowledge may contribute to an increased understanding of brain tumorigenesis in addition to normal CNS development.
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| 25. |
- Engström, Henri
(författare)
-
Effects of Great Cormorant Predation on Fish Populations and Fishery
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The strong increase in number of Great cormorants Phalacrocorax carbo in Sweden in recent years has led to conflicts - particularly with fishery. This thesis focuses on the possible effects of cormorant predation on fish populations. In total, data from 15 lakes in South Sweden were included in this study while most studies were carried out in Lake Ymsen. The results suggest that the impact of cormorant predation on natural fish populations was small, and I observed no decline in fish mass after cormorants established. Cormorant predation on eel was difficult to evaluate because of several confounding factors.Ruffe, roach and perch were the most important prey species to the cormorants and most fish taken were small. Cormorants do not seem to catch species and sizes in proportion to their occurrence in the fish community.Total fish removal by cormorants varied considerably among lakes (0.2-15.0 kg/ha) and cormorant population sizes at the different lakes were significantly positively correlated with fishery catches, which in turn was significantly positively correlated with total phosphorous levels. Thus, cormorant densities in lakes, and perhaps elsewhere, seem to be governed chiefly by fish densities. The fact that cormorant predation appears not to reduce fish densities suggest cormorants to be regulated by other means than prey depletion. The mechanism behind population regulation could be a behavioural response of fish, making fish more difficult to catch for the cormorants.In recent years, cormorant populations have been subjected to intensive legal and illegal actions with the aim to reduce cormorant numbers. However, the actions currently carried are well below the efforts needed to limit population sizes. To conclude, cormorants appear to compete little with fishery, with regards to free-living fish. The main problem is that cormorants sometimes damage and take away fish in fishing gears.
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| 26. |
- Florin, Ann-Britt
(författare)
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Bottlenecks and blowflies : Speciation, reproduction and morphological variation in Lucilia
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis attempts to improve our understanding of the role of population size for the process of speciation. First, the effect of population size on speciation is studied using several meta-analyses of published laboratory experiments. Second, the effect of population size on behaviour is studied using a laboratory population of the blowfly Lucilia sericata. Third, the effect of population size on morphological and genetic variation is studied using wings and microsatellites from wild populations of L. illustris as well as experimentally bottlenecked populations of L. sericata. The meta-analyses showed that the result of many previous laboratory experiments on sympatric and parapatric speciation may have been biased by too small population sizes. Reduced interbreeding was less likely to develop in small populations where the selection against hybridisation often seemed to have been opposed by inbreeding depression or loss of genetic variation. In allopatric speciation experiments, no general consistent effect of population size was observed. There was no support for speciation through founder events. In fact, significant assortative mating was only found in vicariance experiments where derived populations was tested against each other. Population size influenced reproductive behaviour in L. sericata. There was a positive effect of increasing number of males on egg-laying but only as long as the female was in the company of at least one other female. Female mate choice and a positive effect of number of eggs on larval survival are suggested to be the underlying factors. No historic bottlenecks could be detected in the fly populations, but strong genetic indications suggest a fine grained genetic population structure of wild Lucilia flies. Bottlenecks had unpredictable effects on wing morphology as well as on genetic variation and fitness in a laboratory stock of L. sericata. Thus a bottlenecked population will not necessarily have a higher chance of evolving morphological novelties than one which has not undergone a bottleneck. However, among many bottlenecked populations there is a good chance that in at least one of them the conditions will be conducive to morphological change and evolution. In this statistical sense, thus, strong population fluctuations may enhance the probability of speciation events.
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| 27. |
- Fridborg, Ingela
(författare)
-
A genetic approach to the identification of new components regulating development in Arabidopsis thaliana
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two new genes involved in important processes of plant development were identified in the model plant Arabidopsis thaliana. The genes were isolated from mutants generated through insertional mutagenesis based on a transposon tagging approach.The first gene, ALB3, was isolated through the identification of the mutant albino3 (alb3), displaying severe defects in pigmentation and chloroplast biogenesis. The ALB3 protein shows sequence similarity to a yeast protein, OXA1, which is required in the mitochondria for proper assembly of the cytochrome oxidase complex. As ALB3 is localised in thylakoid membranes, we suggest that the ALB3 protein acts in the assembly of thylakoid membrane protein complexes and thereby is crucial for proper chloroplast development and function.The second gene, SHI, was identified through the short internodes (shi) mutation, a dwarfing mutation conferring a phenotype similar to mutants defective in the biosynthesis of the plant hormone gibberellin (GA). However, the shi mutant is unable to elongate following treatment with exogenous GA, which indicates that shi is defective in the response to GA. The level of active GA is elevated in the shi mutant, which is the expected result of reduced feedback control of GA biosynthesis. As the shi mutant phenotype is the result of overexpression of the SHI gene, we suggest that the SHI protein is a component of the GA signalling pathway, possibly acting as a repressor of GA-induced cell elongation.Sequence similarity database searches revealed that the SHI gene belongs to a new Arabidopsis gene family comprising at least eight members (SHI, LRP1, and SRS1 to SRS6). These genes encode regulatory proteins containing a putative zinc-binding RING finger-like domain. We have cloned SRS1 and SRS2, and have shown by overexpression of these genes in transgenic Arabidopsis that their gene products might function in similar processes as SHI.
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| 28. |
- Gertsch, Pia J.
(författare)
-
Adaptive significance of queen mating frequency in ants : In search of benefits of genetic variability
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fitness effects of polyandry, multiple mating by females, were studied on two ant speciesLasius niger and Formica truncorum. Particular emphasis was put on evaluating diploid male load, which happens when homozygosity in the sex determination locus leads to intendedfemales developing into sterile, diploid males. It has been hypothesised that under certainconditions diploid male load selects for polyandry.The power of spermatheca-PCR (genotyping stored sperm in the spermatheca of a femaleinsect) in identifying multiply mated females was scrutinised. Microsatellite amplificationsfrom artificial sperm mixes with known composition showed that alleles at and above 10%representation are reliably amplified and detected.Microsatellite markers were developed for L. niger and female survival and fecundityin relation to her mate number were studied in two populations: Uppsala, Sweden and Lausanne, Switzerland. Annual sexual production did not correlate with higher female mating frequency in either population. Colony survival appeared to be higher for multiple mated females in Lausanne but not in Uppsala. The possible higher survival of multiple mated queens is unlikely to be due to diploid male load as there was no sign of diploid males among broods of 479 queens which were kept in laboratory.Diploid male load in the colonies of the ant Formica truncorum was measured. Thecolony size was significantly negatively affected by diploid male production. However, theobserved frequencies of diploid males in the colonies did not comply with the theoreticalpredictions. Until the determinants of diploid male production in F.truncorum are clarified itis not possible to settle whether diploid male load selects for multiple mating in this species.A theoretical model was constructed to examine how the selection on mating frequencyfrom diploid male load changes when allelic diversity in the sex determination locus increases.Fitness of single and double mated females was compared. The fitness difference between themate number classes rapidly decreases when the number of alleles in the sex determinationlocus increases. Moreover, even when the selection pressure from diploid male production ismost extreme, the fitness differences between single and double mated females are small.Diploid male load probably is not strong enough a force to drive mating frequency evolutionin eusocial insects.
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| 29. |
- Ginjala, Vasudeva, 1969-
(författare)
-
Transcriptional Silencing in the Imprinted Igf2-H19 Loci: The Mystique of Epigenetics
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Genomic imprinting marks a subset of autosomal loci expressed in parent of origin-dependent monoallelic expression in a non-Mendelian fashion. To restore totipotency and to reset the imprint according to the sex of the individual, the mark must be erased during germline development. The imprinted Igf2-H19 loci located distally on chromosome 7 in mouse and 11p15.5 in human, share common regulatory elements that regulate differential expression. Where the H19 is silenced when paternally inherited, the Igf2 is silenced when maternally inherited. The differentially methylated 5'-flank of H19 gene, termed imprinting control region (ICR), shown to display a unique chromatin organisation harbours hypersensitive sites in linker regions flanked by positioned nucleosomes on the maternal allele. This unique chromatin conformation functions as a methylation-sensitive and unidirectional chromatin insulator, which later was found to depend on the chromatin insulator protein CTCF. The H19 ICR exhibits default-silencing functions in promoter-proximal positions. The maximal distance between the H19 ICR and the promoter of the reporter gene required for this effect was 1.2 ± 0.3kb which can be compared to the 1.9 kb distance between the endogenous H19 ICR and H19 promoter. Results suggest that the H19 ICR adopts a chromatin conformation that must be separated by a minimal distance from pivotal cis-regulatory elements to avoid adverse effects on neighbouring promoters. Poly(ADP-ribosy)lation represents a novel post-translational epigenetic mark that segregates with exclusively the maternal derived H19 ICR and associated with factors that interact with the CTCF target sites. CTCF is itself poly(ADP-ribosy)lated and the poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide relieves the insulator function of the H19 ICR. Designed zinc finger proteins were applied to examine if epigenetic marks provided an obstacle for targeted activation and silencing. The zinc finger protein ZFP809 with activator/repressor domain able to efficiently activate/silence the IGF2 target. Murine hybrid cell lines of human chromosome 11, demonstrated that the ZFP809 overcame the epigenetic marks that repressed maternal IGF2 and paternal H19 allele, respectively. Results suggested that imprinted genes are not normally exposed to strong cis-regulatory elements and that the designed ZFPs can be exploited to develop a therapeutic method for rectifying epigenetic lesions.
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| 30. |
- Granberg, Lizette
(författare)
-
Bioactivation and binding of polycyclic aromatic hydrocarbons in blood vessel endothelia
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants formed by incomplete combustion of organic materials such as fossil fuels and wood. Experimental and epidemiological studies indicate that PAHs may be involved in the development of cardiovascular disease. In vivo and in vitro studies were carried out to examine whether blood vessel endothelia are potential targets for PAH toxicity in mammals and birds. Tissues and cells that are sites for irreversible binding of benzo(a)pyrene (B(a)P) and 7,12-dimethylbenz(a)anthracene (DMBA), were identified in mice, rats and chicken embryos, using autoradiographic techniques. Binding of DMBA and the heterocyclic amine 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) was examined in cultured human umbilical vein and artery endothelial cells (HUVEC and HUAEC). Enzyme inducers and inhibitors were used to elucidate involvement of cytochrome P4501A (CYP1A) in local metabolite binding. Furthermore, the CYP1A-related enzyme activities 7-ethoxyresorufin 0-deethylase (EROD) and DMBA hydroxylase were determined in the tissues. In animals exposed to a CYP1A-inducer (3,3',4,4',5-pentachlorobiphenyl or β -naphthoflavone), irreversible B(a)P and DMBA binding was observed in endothelial cells in certain arteries, veins and capillary networks. There was no significant binding in endothelia from control animals. CYP1A- induction also increased DMBA and Trp-P-1 binding in HUVEC, but not in HUAEC. The formation of bound metabolites in endothelial cells generally correlated with induction of EROD and DNMA hydroxylase. In conclusion, PAHs can be metabolically activated in blood vessel endothelia in several organs, including heart, lung and brain, in rodents and chicken embryos as well as in cultured HUVEC. The results imply endothelial cells as targets for chemical toxicity, although different endothelia exhibit major differences in bioactivation ability.
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| 31. |
- Gunnarsson, Urban
(författare)
-
Vegetation changes on Swedish mires : Effects of raised temperature and increased nitrogen and sulphur influx
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the start of the industrialisation, the deposition of nitrogen and sulphur and the atmospheric concentrations of greenhouse gases have increased. The main objectives of this study were to find how these changes in climate and deposition can change the vegetation of mire ecosystems and the growth of Sphagnumspecies. Two main approaches were applied: re-investigated of two mires previously investigated 40-50 years ago and experiment manipulations. The plant species diversity had decreased on one of the two re-investigated mires (Skattlösbergs Stormosse; central Sweden), but the total number of species was unchanged on the other (Åkhultmyren; southern Sweden). On Skattlösbergs Stormosse, an acidification was found in the high pH areas, coinciding with reduction in rich fen species. At Åkhultmyren, there was a similar reduction in pH, but the changes in the plant composition also indicated increased nutrient levels and a drier mire surface. Therwere large changes in species composition on Åkhultmyren. For instance Scheuchzeria palustris had disappeared from the investigated area. Further, the cover of Scots pine (Pinusylvestris) had increased, which can be explained by a changed ground-water table regime. Monitoring of pines growing on a bog over a ten-year period showed that pines growing higher above the ground-war table had higher survival than lower-growing pines.Experimental addition of nitrogen during 3-4 years reduced Sphagnum growth in bogs and poor fens repressenting a wide range of ambient nitrogen deposition. A changed interspecific competitive relation was found between S. lindbergand S. balticum when increasing nitrogen influx, but the competitive relations between two hummock-growing species pairs did not change in a three-year nitrogen fertilization study. Sulphur additiodid not affect the production or length increment in S. balticum. An increased temperature reduced Sphagnum growth, but there were no indications of altered competitive relationshipbetween hummock and hollow inhabiting Sphagnum species in a four-year experiment.
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| 32. |
- Gustafsson, Christel, 1968-
(författare)
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Plant Population Dynamics and Biotic Interactions in two Forest Herbs
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Sweden today, deciduous woodlands are often restricted to small isolated remnants of what it once was. Managing practices have changed concerning both cattle grazing and logging. Thus, dispersal, habitat requirements and their importance for forest species distributions become a relevant issue. Most of the species found in the deciduous flora are perennial herbs. I have examined population dynamics in the forest perennial Sanicula europaea, and its relation to environmental factors such as grazing, competition and spatial and temporal variation in such factors. Moreover I examined species distributions in relation to dispersal and habitat suitability in S. europaea and Dentaria bulbifera. To understand mechanisms behind the observed patterns I performed a number of experiments.The results clearly demonstrated that the distribution and abundance of S. europaea was not dispersal limited, whereas the opposite held true for D. bulbifera. Moreover, mollusc exclusion increased recruitment thus influencing population dynamics in D. bulbifera. Leaf losses had negative effects on S. europaea individuals. These negative effects depended both on the extent, frequency and timing of the leaf losses and early losses were more severe than late. Population level effects of grazing were not negative as negative direct effects were counterblanced by positive indirect effects. The positive effects of grazing were mainly in terms of an increased recruitment. In S. europaea, high variation in a life cycle transition was always coupled to low elasticity, and traits that varied much due to the examined environmental factors had little importance to population growth rate. A population level perspective is required to assess total effects of environmental factors. In perennial organisms such evaluations need to calculate integrated measures of the effects over the entire life cycle. Field studies spanning several years and demographic models are important to achieve these objectives.
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| 33. |
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| 34. |
- Hanson, Johannes
(författare)
-
Functional characterization of the pointed cotyledon subclass of HDZip genes in Arabidopsis thaliana
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Genes encoding homeodomain leucine zipper, HDZip, transcription factors constitute a large gene family in Arabidopsis thaliana. In this thesis the isolation and characterization of four HDZip genes (ATHB3, -13, -20 and -23) is described. These genes are similar in sequence and form a distinct subclass within the HDZip gene family. Since the genes cause similar alterations in cotyledon shape when expressed constitutively, we refer to the members of this subclass as pointed cotyledon HDZip genes. To determine the biological functions of the genes, the phenotypes of plants constitutively expressing the genes have been analysed. Each of the genes specifically inhibits lateral cell expansion in cotyledons and leaves and thereby causes them to be abnormally narrow. Detailed expression analysis shows that only ATHB23 is expressed in the entire leaf and cotyledon from early stages of development while ATHB20 is predominantly expressed in the root cortex. ATHB13 is expressed in basal parts of mature leaves and floral organs and ATHB3 in root and stem cortex. The ATHB13 protein acts within a signalling pathway that mediates a response to sucrose that specifically regulates the expression of specific sugar-regulated genes. ATHB3 specifically inhibits primary root development without affecting the development of secondary roots when constitutively expressed. Reduced expression of ATHB3 by antisense suppression results in increased expression of ATHB13, indicating that ATHB3 acts as a repressor of ATHB13 expression in the wild type.This thesis also reports the isolation of seven new genes of HDZip class I and reviews available functional information on the genes in this class. One conclusion is that HDZip I proteins that are closely related phylogenetically are also functionally related, in most cases. Seven different mutations in HDZip I genes were also identified. The lack of phenotypic deviations from wild type of these mutants suggests that these HDZip proteins act in a redundant fashion in the plant.
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| 35. |
- Hedengren Olcott, Marika, 1970-
(författare)
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Relish and the Regulation of Antimicrobial Peptides in Drosophila melanogaster
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fruit fly Drosophila melanogaster has been a powerful model system in which to study the immune response. When microorganisms breach the mechanical barrier of the insect, phagocytosing cells and a battery of induced antimicrobial molecules rapidly attack them. These antimicrobial peptides can reach micromolar concentrations within a few hours. This immediate response is reminiscent of the mammalian innate immune response and utilizes transcription factors of the NF-κB family. We have generated loss-of-function mutants of the NF-κB-like transcription factor Relish in order to investigate Relish's role in the Drosophila immune response to microbes. Relish mutant flies have a severely impaired immune response to Gram-negative (G-) bacteria and some Gram-positive (G+) bacteria and fungi and succumb to an otherwise harmless infection. The main reason for the high susceptibility to infection is that these mutant flies fail to induce the antimicrobial peptide genes. The cellular responses appear to be normal. Relish is retained in the cytoplasm in an inactive state. We designed a set of expression plasmids to investigate the requirements for activation of Relish in a hemocyte cell line after stimulation with bacterial lipopolysaccharide. Signal-induced phosphorylation of Relish followed by endoproteolytic processing at the caspase-like target motif in the linker region released the inhibitory ankyrin-repeat (ANK) domain from the DNA binding Rel homology domain (RHD). Separation from the ANK domain allowed the RHD to move into the nucleus and initiate transcription of target genes like those that encode the inducible antimicrobial peptides, likely by binding to κB-like sites in the promoter region. By studying the immune response of the Relish mutant flies in combination with mutants for another NF-κB-like protein, Dorsal-related immunity factor (Dif), we found that the Drosophila immune system can distinguish between various microbes and generate a differential response by activating the Toll/Dif and Imd/Relish pathways. The recognition of foreign microorganisms is believed to occur through pattern recognition receptors (PRRs) that have affinity for selective pathogen-associated molecular patterns (PAMPs). We found that the Drosophila PRRs can recognize G- bacteria as a group. Interestingly, the PRRs are specific enough to distinguish between peptidoglycans from G+ bacteria such as Micrococcus luteus and Bacillus megaterium and fungal PAMPs from Beauveria bassiana and Geotrichum candidum. This thesis also investigates the expression of the antimicrobial peptide genes, Diptericin B and Attacin C, and the putative intracellular antimicrobial peptide gene Attacin D, and explores a potential evolutionary link between them.
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| 36. |
- Heidmarsson, Starri
(författare)
-
Taxonomy and phylogeny of Dermatocarpon (Verrucariales, lichenized Ascomycotina) with special emphasis on the Nordic species
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis Dermatocarpon (Verrucariales, lichenized Ascomycotina) of the Nordic countries is revised. Useful characters for species identification are epinecral layer type, spore length, medulla sensitivity to Melzer´s Reagent, and lower surface colour anappearance. The pruinosity of certain members of Dermatocarpon, which earlier was considered an important character, is caused by an epinecral layer consisting of air filled cells. In all eight species Dermatocarpon in the Nordic countries are accepted.The relationships of D. bachmannii and D. deminuens are studied in detail using statistical methods. Both PCA and t-test are utilized and the results indicate that although the two species are closely related they should be treated as distin species.Dermatocarpon miniatum is a common and widely distributed species which shows a considerable morphological plasticity. The D. miniatum-complex is studied by molecular methods. The ITS and 5.8S areas of the rDNA were sequenced for 25 representatives of the D. miniatum-complex and 21 representatives of other Dermatocarpon species. D. leptophyllum, D. linkolae, and D. miniatum var. cirsodes are monophyletic units, but considered synonyms of D. miniatum. D. miniatum var. miniatum and D. miniatum var. complicatum are polyphyletic and should not be treateds separate taxa. An undescribed species similar to D. miniatum from the southern part of North America is discussed.
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| 37. |
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| 38. |
- Höglund, Erik
(författare)
-
Neuroendocrinology of agonostic interaction and social signalling in Artic charr (Salvelinus alpinus) : Studies on the neuroendocrine regulation of aggressive behaviour, stress responses and skin colour
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis shows that socially subordinate Arctic charr (Salvelinus alpinus) display elevated brain serotonergic (5-HT) and norepinephric activity along with a chronic activation of the hypothalamic-pituitary-interrenal (HPI) axis, including elevated plasma concentrations of á-MSH. Furthermore, subordinate fish showed an inhibition of aggressive behaviour and darker body coloration, skin darkness being positively correlated with plasma á-MSH. Fish kept on dark background, and thus being darker in body colour, were less aggressive than conspecifics interacting on white background, supporting the hypothesis that skin darkening could signal social submission. The 5-HT1A -receptor agonist 8-OH-DPAT stimulated HPI axis activity in non-stressed fish, but if administrated to stressed fish it inhibited HPI axis activity, suggesting that 5-HT1A receptors may act as both post- and pre-synaptic receptors. 8-OH-DPAT also induced skin darkening in both non-stressed and stressed fish. Stimulation of brain dopaminergic activity by L-dopa treatment counteracted the stress-induced inhibition of aggressive behaviour, and stress related effects on brain 5-HT activity and plasma levels of cortisol. In conclusion, social subordination in Arctic charr results in skin darkening and an inhibition of aggressive behaviour. Stress-induced effects, that could be mediated by elevated brain 5-HT activity, and serve as a way of signalling social position and coping with stress.
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| 39. |
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| 40. |
- Johannesson, Henrik
(författare)
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Functional analysis of homeodomain-leucine zipper transcription factors in Arabidopsis thaliana
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Homeodomain-leucine zipper (HDZip) proteins constitute a large family of transcription factors apparently unique to plants. To elucidate the function of these factors, the biochemical properties in vitro as well as the effects on transgenic plants when expressed at high levels were studied. The conclusion is that HDZip proteins are very similar with respect to DNA-binding specificity in vitro but appear to be active in different aspects of plant development. Thus, functional specificity of HDZip proteins is most likely determined by other aspects of proteins function, e.g. their capacity to interact with other proteins. High-level expression of the HDZip gene ATHB5 in transgenic plants results inhypersensitivity to the inhibitory effect of the plant hormone abscisic acid (ABA) on seed germination and seedling root growth. Furthermore, the expression of ATHB5 in germinating seedlings is downregulated in the Arabidopsis ABA response mutants abi3 and abi5. Together, these data suggest that ATHB5 acts as a regulator of seed germination and postgerminative growth downstream of ABI3 and ABI5 in an ABA response-signaling pathway. Enhanced levels of the HDZip gene ATHB13 in transgenic Arabidopsis confer a sugar-dependent reduction of cotyledon width. In addition, a subset of known sugar-dependent genes was hyperinduced by sucrose in Arabidopsis seedlings overexpressing ATHB13. These data suggest that ATHB13 affects both cotyledon morphology and gene regulation as a component of a sucrose-signaling pathway. Loss-of-function mutations in ATHB5 and ATHB13 did not result in any discernable mutant phenotypes, suggesting that these genes are only required under specific physiological conditions or that they act in a redundant fashion in the plant.
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| 41. |
- Johanson, Zerina, et al.
(författare)
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The braincase and palate of the tetrapodomorph sarcopterygian Mandageria fairfaxi: morphological variability near the fish-tetrapod transition
- 2003
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 46:2, s. 271-293
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Tidskriftsartikel (refereegranskat)abstract
- The braincase of the Late Devonian tristichopterid sarcopterygian Mandageria fairfaxi, from Canowindra, NSW, Australia, differs radically from the conservative pattern present in other 'osteolepiforms' (stem–group tetrapodomorph fishes) and non–dipnoan sarcopterygian fishes in general. The basioccipital region is short, displaced anteriorly, and either unossified or loosely articulated to the exoccipital, leaving most or all of the notochordal tunnel open ventrally. The exoccipital complex, which is developed into a large saddle that would have rested on top of the notochord, carries large, triangular articular facets on its posterior face and appears to have formed part of a functional neck joint, a synovial articulation between the skull and vertebral column that allows the former to rotate against the latter. Such a joint is characteristic of post–Devonian tetrapods, but unknown in other sarcopterygians. We infer that the ventrally open notochordal tunnel allowed gentle flexion of the cranial notochord during (predominantly vertical) rotational movement at the occiput; this is a mechanically unique solution to the problem of creating a mobile neck. Other unusual features of Mandageria include a posteriorly located lateral commissure, and structures on the entopterygoid and lateral commissure that may have been associated with an elaborate spiracular tract.
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| 42. |
- Johansson, Tomas
(författare)
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Habitat selection, nest predation and conservation biology in a Black-tailed Godwit (Limosa limosa) population
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on a black-tailed godwit (Limosa limosa) population, consisting of 35-40 pairs, that breeds on a grazed shore meadow on SE Gotland, Sweden. The small size of the population makes it more prone to extinction due to chance events, than a larger population.The godwits showed microhabitat preferences when choosing nest sites. Godwit nests had higher vegetation over the nest cup, lower surrounding (1-3 m) vegetation and different plant species composition, as compared to random sites. Breeding near conspecifics or other wader species, especially lapwings (Vanellus vanellus) and further away from potential predator perches were the most important factors in decreasing nest predation. A comparison between different shore meadows along the east coast of the island revealed that large, open areas suffered less from nest predation. Thus, shore meadows suitable for breeding godwits should be large and without trees or other predator perches and have a grazing regime that favours variation in vegetation height.Over 80% of previously ringed adults returned each year, but very few birds ringed as chicks were recovered. Hatching success was 55-60% for all observed nests. To predict the future of the current population, demographic data were used in an ecological risk analysis. The simulations showed that the Gotlandic population will not survive the coming 40 years without immigration.Black-tailed godwits are divided into three subspecies. Genetic analyses (mtDNA) revealed that all subspecies had unique haplotypes and there was a clear geographic structure among subspecies. Within the limosa subspecies, godwits on Gotland and Öland showed a high proportion of rare haplotypes, but no genetic variation was found in Dutch birds. These results imply that black-tailed godwits on Gotland and Öland have high conservation value.
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| 43. |
- Kahlert, Maria
(författare)
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Biomass and Nutrient Status of Benthic Algae in Lakes
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For a complete picture of the lake ecosystem, it is necessary to understand the mechanisms regulating biomass and nutrient status (nutrient limitation, optimal supply, or surplus) of benthic algae, which are important primary producers and a food resource for grazers. This thesis gives an overview of the natural variation of benthic algae at different scales of space and time and on different substrates, and unravels some of the underlying factors. Algal nutrient status was assessed using the C:N:P (carbon:nitrogen:phosphorus) ratio of the entire natural benthic community. A review, observations, and experiments confirmed that a C:N:P ratio of about 158:18:1 (molar basis) represented an optimal nutrient supply, and that substantially higher C:N, N:P, or C:P ratios reflected algal growth limitation caused by an N or P nutrient deficiency. Horizontal variation of benthic algal biomass and nutrient status was patchy, of similar amount for all investigated distances, substrates, and lakes, and constituted a dominant proportion of the total variation. For example, patches of nutrient limited algae were found within only 10 m distance from patches with a nutrient surplus. Thus, horizontal variation should not be neglected when sampling benthic algae in lakes. Field observations suggested an impact of wind, nutrients, and grazers on the horizontal variation. Light and nutrients might have caused the observed vertical and temporal variation. Field experiments confirmed a simultaneous control of benthic algal biomass by nutrients and grazing, mediated by light and temperature. Grazing effects were larger than nutrient effects, but the comparison of natural communities in lakes of different trophy suggested that benthic algal biomass was controlled by nutrients in the long run. An important nutrient supply was animal excretions, causing a low C:N:P ratio of epizoon on zebra mussels, and algal communities associated with macrograzers. A field experiment revealed that 15N circulated one week longer in epizoon associated with a sessile caddisfly than in surrounding epilithon. In conclusion, the regulation of benthic algal biomass and nutrient status in lakes is complex, and benthic animals should be looked at not only as grazers, but also as a nutrient source.
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| 44. |
- Karlsson, Anna
(författare)
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Reproduction in the Hermaphrodite Aeolidiella glauca - A Tale of Two Sexes
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on reproduction in a simultaneous hermaphrodite with internal fertilization; the nudibranch Aeolidiella glauca. Unlike most other nudibranchs, where copulation is the rule, A. glauca was found to transfer sperm via external spermatophores that were attached to the partner's back. Despite elaborate courtship the actual spermatophore transfer, which always involved two animals only, was of short duration. In most matings (88%) spermatophores were reciprocally exchanged. A. glauca was further found to be very promiscuous. During mating and sperm transfer the receiver exerts considerable control over sperm, and manipulative behaviours designed to increase the donor's reproductive success are thus likely to have evolved. An example of such manipulative behaviour may be A. glauca's unique spermatophore avoidance behaviour. I found that slugs carrying a sign of previous mating activity, i.e. a spermatophore, were discriminated against in a situation where mate choice was possible. The presence of spermatophores was further found to reduce slugs' ability to interrupt matings, and displace other slugs. Body size, however, had no direct effect on displacement in A. glauca as small slugs interrupted matings as successfully as large ones. Furthermore, pair formation and mating were found to be random with respect to size. This was true also for pairs formed in the field. In addition to mate choice hermaphrodites may increase their reproductive success by differential sex allocation. I tested whether differing mate encounter rates had any effects on allocation to male and female function in A. glauca. Slugs with more mating opportunities mated more, and had higher proportional spermatophore production that others. As predicted they also laid significantly fewer eggs than slugs presented with partners less often.
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| 45. |
- Kolterud, Åsa, 1973-
(författare)
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The Role of Lhx2 During Organogenesis : - Analysis of the Hepatic, Hematopoietic and Olfactory Systems
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During embryonic development a variety of tissues and organs such as the lung, eye, and kidney are being formed. The generation of functional organs is regulated by reciprocal cell-cell interactions. Via the secretion of soluble molecules one type of cells affect the fate of their neighboring cells. A central issue in organogenesis is how a cell interprets such extrinsic signals and adopts a specific fate, and how the cell in response to this signal establishes reciprocal signaling. Transcription factors play a critical role in this process and my thesis focuses on the role of the LIM-homeodomain transcription factor, Lhx2, in the development of three different organ systems, the liver, the hematopoietic system and the olfactory system.The liver is formed from endoderm of the ventral foregut and mesenchyme of the septum transversum (st) and its development depends upon signaling interactions between these two tissues. As the liver becomes a distinct organ it is colonized by hematopoietic cells and serves as hematopoietic organ until birth. The fetal liver provides a microenvironment that supports the expansion of the entire hematopoietic system (HS) including the hematopoietic stem cells (HSCs). Liver development in Lhx2-/- embryos is disrupted leading to a lethal anemia due to insufficient support of hematopoiesis. To further investigate the role of Lhx2 in liver development I analyzed gene expression from the Lhx2 locus during liver development in wild-type and Lhx2-/- mice. Lhx2 is expressed in the liver associated st mesenchymal cells that become integrated in the liver and contribute to a subpopulation of hepatic stellate cells in adult liver. Lhx2 is not required for the formation of these mesenchymal cells, suggesting that the phenotype in Lhx2-/- livers is due to the presence of defective mesenchymal cells. The putative role of Lhx2 in the expansion of the HS was examined by introducing Lhx2 cDNA into embryonic stem cells differentiated in vitro. This approach allowed for the generation of immortalized multipotent hematopoietic progenitor cell (HPC) lines that share many characteristics with normal HSCs. The Lhx2-dependent generation of HSC-like cell lines suggests that Lhx2 plays a role in the maintenance and/or expansion of the HS. To isolate genes putatively linked to Lhx2 function, genes differentially expressed in the HPC lines were isolated using a cDNA subtraction approach. This allowed for the identification of a few genes putatively linked to Lhx2 function, as well as several stem cell-specific genes. The antagonist of Wnt signalling, Dickkopf-1 (Dkk-1), was identified in the former group of genes as it showed a similar expression pattern in the fetal liver, as that of Lhx2 and expression of Dkk-1 in fetal liver and in HPC lines appeared to be regulated by Lhx2. This suggests that Dkk-1 plays a role in liver development and/or HSC physiology during embryonic development.During development of the olfactory epithelium (OE) neuronal progenitors differentiate into mature olfactory sensory neurons (OSNs) that are individually specified into over a thousand different subpopulations, each expressing a unique odorant receptor (OR) gene. The expression of Lhx2 in olfactory neurons suggested a potential role for Lhx2 in the development of OSNs. To address this OE from Lhx2-/- and wild-type mice was compared. In the absence of functional Lhx2 neuronal differentiation was arrested prior to onset of OR expression. Lhx2 is thus required for the development of OSN progenitors into functional, individually specified OSNs.Thus, Lhx2 trigger a variety of cellular responses in different organ systems that play important roles in organ development in vivo and stem cell expansion in vitro.
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| 46. |
- Kourmouli, Niki, et al.
(författare)
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Heterochromatin and tri-methylated lysine 20 of histone H4 in animals
- 2004
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Ingår i: Journal of Cell Science. - : The Company of Biologists. - 0021-9533 .- 1477-9137. ; 117:14, s. 2491-2501
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Tidskriftsartikel (refereegranskat)abstract
- Tri-methylated lysine 20 on histone H4 (Me(3)K20H4) is a marker of constitutive heterochromatin in murine interphase and metaphase cells. Heterochromatin marked by Me(3)K20H4 replicates late during S phase of the cell cycle. Serum starvation increases the number of cells that exhibit high levels of Me(3)K20H4 at constitutive heterochromatin. Me(3)K20H4 is also present at the centromeric heterochromatin of most meiotic chromosomes during spermatogenesis and at the pseudoautosomal region, as well as at some telomeres. It is not present on the XY-body. During murine embryogenesis the maternal pronucleus contains Me(3)K20H4; Me(3)K20H4 is absent from the paternal pronucleus. On Drosophila polytene chromosomes Me(3)K20H4 is present in a `punctate pattern' at many chromosomal bands, including the chromocenter. In coccids it is present on the facultatively heterochromatinised paternal chromosome set. We also present evidence that Me(3)K20H4 is dependent upon H3-specific Suv(3)9 histone methyltransferase activity, suggesting that there may be `epigenetic cross-talk' between histones H3 and H4.
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| 47. |
- Lind, Maria I.
(författare)
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Characterisation of some iron proteins in Drosophilia melanogaster and Pacifastacus leniusculus
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cDNA cloning of the 76-kDa protein, an immune protein from crayfishhaemocytes, shows that it is similar to a family of haem-containing peroxidases.In addition to its cell adhesion activity it has also peroxidase activity, and theprotein was named peroxinectin. The cell adhesion is probably mediated by aKGD-motif present in peroxinectin.In mammals, the iron-regulatory proteins (IRP) can bind the iron-responsive element (IRE), present in the mRNAs of some iron proteins andthereby regulate their expression. IRPs are also present in the invertebrates,Drosophila melanogaster, and Pacifastacus leniusculus. Two DrosophilaIRP1s, IRP1A and IRP1B, were cloned. Recombinant IRP1A binds specifically toIREs and both IRP1A and IRP1B have aconitase activity. The Drosophilamitochondrial aconitase (mAc) was cloned and shows similarity to the IRPs.Interestingly, the Drosophila mAc mRNA lacks the IRE, in contrast tomammalian mAc transcripts, which have IREs. This supports the idea thatDrosophila has another IRP regulated step in the citric acid cycle.Several transcripts encoding the same ferritin subunit in D.melanogaster were isolated. These transcripts are generated by alternativesplicing and differential poly-adenylation. The expressions of these aredevelopmentally regulated, and are modulated in response to the iron level. AnIRE is present within the alternatively spliced intron. Furthermore, the transcriptencoding crayfish ferritin has an atypical IRE. Both the Drosophila and crayfish ferritin IREs bind specifically to IRPs.Translocation of iron and other metal-ions through the bilipidmembrane is depending on transport systems, and in Drosophila three members of the ZIP family of metal-ion transporters were identified and their expression was studied.
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| 48. |
- Lind, Monica
(författare)
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Organochlorines and bone : Effects of organochlorines on bone tissue morphology, composition and strength
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- From results presented during the last decade, it is obvious that the skeleton is a targetorgan for a number of persistent organochlorines. So far, however, little attention hasbeen paid to this subject. This thesis examines the effects of one such compound, the ubiquitous PCB-congener, 3,3',4,4',5-pentachlorobiphenyl (PCB126), on rat bone morphology, composition and strength. The impact of a cocktail of persistent organic pollutants (POPs) on bone mineral density in Baltic grey seal and in a small population of Swedish males was also studied. It was found that PCB 126 induced profound alterations in the long bones of the rat;including increased cortical thickness, increased trabecular mineral density, decreasedmarrow cavity, decreased collagen content, structural changes of the collagen molecule and impairment of mechanical characteristics, such as decreased maximum torqueand decreased stiffness. The mechanisms underlaying these effects are not known, butthe effects obtained cannot be explained either by changes in vitamin C and vitamin Alevels, or by disturbances of the sex endocrine system. By peripheral quantitative computed tomography (pQCT) of grey seal bone specimens, thissis also shows that mineral density of trabecular bone was reduced, as in human osteoporosis, during the period of maximum PCB and DDT contamination of the Baltic (1965 - 1985). An epidemiological study on Swedish males indicated a negative relation between bonemineral density and blood levels of the DDT metabolite p,p'-DDE. This implies the possibility that organochlorines may act as skeleto-toxic agents in humans, even at low exposure levels.
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| 49. |
- Lindgren, Gabriella
(författare)
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Genome mapping of the horse
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our ability to map and sequence whole genomes is one of the most important developments in biological science. It will provide us with an unprecedented insight into the genetic background of phenotypic traits, such as disease resistance, reproduction and growth and also makes it feasible to study the processes of genome evolution. The main focus of this thesis has been to develop a linkage map of the horse (Equus caballus) genome. A secondary aim was to expand the number of physically mapped genes in the horse, allowing comparative analyses with data from the human genome map. Finally, attempts were made to identify single nucleotide polymorphisms (SNPs) on the horse Y chromosome. The development of a genome map relies on the information generated by both linkage and cytogenetical studies. To integrate genetical and physical assignments in the very early phase of equine genome map construction, 19 polymorphic microsatellite markers were isolated from lambda phage clones which, in parallel, were physically assigned to chromosomes by fluorescent in situ hybridization (FISH). The microsatellites were simultaneously mapped by linkage analysis in a Swedish reference pedigree. A first primary male autosomal linkage map of the domestic horse was constructed by segregation analysis of 140 genetic markers within eight half-sib families with, in total, 263 offspring. One hundred markers were arranged into 25 linkage groups, 22 of which could be assigned physically to 18 different chromosomes. The total map distance contained within linkage groups was 679 cM. The presented map provides an important framework for future genome mapping in the horse. Our contribution to the comparative horse genome map, was the presentation of map data for 12 novel genes using FISH and somatic cell hybrid mapping. AD chromosomal assignments except one were in agreement with human-horse Zoo-FISH data. The exception concerned the CLU gene which was mapped by synteny to ECA2 while human-horse Zoo-FISH data predicted that it would be located on ECA9. The level of SNPs on the horse Y chromosome was also investigated by DNA sequencing and denaturing high performance liquid chromatography (DHPLC) of Y chromosome-specific fragments derived mainly from BAC clone subcloning. The amount of genetic variability was found to be very low, consistent with low male effective population size.
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| 50. |
- Lindhe, Örjan, 1968-
(författare)
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Adrenal Bioactivation and Toxicity of 3-MeSO2-DDE, o,p´-DDD and DMBA Investigated in Tissue Slice Culture
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I developed a precision-cut adrenal slice culture procedure to investigate cytochrome P450 (CYP) catalysed irreversible binding and adrenocorticolytic effects in human, rodent, and fish adrenal tissue, ex vivo. Autoradiography and radioluminography of exposed tissue slices showed that the potent adrenal toxicant 3-methylsulphonyl-2,2´-bis(4-chlorophenyl)-1,1´-dichloroethene (MeSO2-DDE) causes a selective metabolite binding in zona fasciculata (ZF), which is diminished by the CYP11B1 inhibitor metyrapone. MeSO2-DDE also reduces corticosterone secretion, increases 11-deoxycorticosterone secretion and causes mitochondrial degeneration in ZF cells in cultured mouse adrenal slices. ACTH treatment of mice induces CYP11B1 and increases irreversible MeSO2-DDE binding and toxicity in ZF cells. Metyrapone-sensitive binding of MeSO2-DDE is also observed in human zona fasciculata/reticularis (ZF/ZR) and 11-deoxycorti- sol/corticosterone secretion increases in MeSO2-DDE-exposed cultured human adrenal slices. The adrenocorticolytic drug 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichlorethane (o,p´- DDD, Mitotane®) is also bound in ZF/ZR but does not to impair hormone secretion in human adrenal slices at equimolar concentration. A targeted, presumably CYP1B1-catalysed irreversible binding of the adrenocorticolytic carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) in ZF/ZR occurs in rat adrenal slices, whereas presumably CYP1A1-catalysed irreversible binding in endothelial cells is observed in CYP1-induced rats and mice. The rat-specific adrenocorticolytic activity of DMBA may rely on two independent pathological processes resulting in cell death and haemorrhage in the adrenal cortex. In Atlantic cod, selective binding of o,p´-DDD is observed in interrenal cells in cultured anterior kidney slices.In conclusion, precision-cut adrenal slice culture is a simple ex vivo test system with which to investigate CYP-catalysed metabolite binding, alteredsteroid hormone secretion and target cell ultrastructure in human, experimental and wild animal tissue. The results imply that organisms under stress could be at increased risk of MeSO2-DDE induced adrenal toxicity. MeSO2-DDE is an expected human adrenal toxicant, which should be evaluated as a possible alternative in the therapy of adrenocortical hypersecretion and tumour growth.
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