| 1. |
- Tatarenkov, Andrey, et al.
(författare)
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Evidence of a reproductive barrier between two forms of the marine periwinkle Littorina fabalis (Gastropoda)
- 1998
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Ingår i: Biological Journal of the Linnean Society. - 0024-4066. ; 63:3, s. 349-365
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Tidskriftsartikel (refereegranskat)abstract
- Studies of allozyme variation may reveal unexpected patterns of genetic variation which challenge earlier conclusions of species delimitations based on morphological data. However, allozyme variation alone may not be sufficient to resolve this kind of problem. For example, populations of the marine intertidal snail Littorina fabalis (= Littorina mariae) from wave exposed parts and from protected parts of the same shores are distinguished by different alleles of arginine kinase (Ark) while indifferent, or very nearly so, in another 29 loci. Intermediate populations have large deficiencies of exposed/sheltered heterozygote classes of Ark and we have earlier suggested habitat-related selection in this locus as the explanation. In this study we estimated growth rate of individual snails of different Ark-genotypes in three different habitats (exposed, sheltered and intermediate). In all habitats the snails homozygous for alleles of 'exposed' type grew faster and matured at a larger size than did snails homozygous for alleles of 'sheltered' types. This relationship was indirectly confirmed in three additional sites of intermediate exposure where exposed Ark-genotypes dominated among large (>8 mm) snails while the sheltered genotypes dominated among small (<5 mm) snails of truly sympatric samples. We furthermore found small differences in allele frequencies of two other loci (Pgi and Pgm-2) and in shell colour frequencies, comparing sympatric snails of exposed and sheltered Ark-homozygotes. Although we found no signs of habitat-related selection among snails of different Ark-genotype, or selection against heterozygotes, we cannot reject selection in Ark, as our experiments only covered one island, one season and grown-up snails. The coupling between allozyme and phenotypic characters in strictly sympatric samples of snails suggests the presence of two gene pools. Perhaps the large and small forms of L. fabalis represent very closely related cryptic taxa. However, introgression between them seems a possible explanation for the striking similarities in the vast majority of morphological and allozyme characters. (C) 1998 The Linnean Society of London.
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| 2. |
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| 3. |
- Beier, Frank, et al.
(författare)
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Localization of silencer and enhancer elements in the human type X collagen gene.
- 1997
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Ingår i: Journal of Cellular Biochemistry. - : John Wiley & Sons. - 0730-2312 .- 1097-4644. ; 66:2, s. 210-218
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Tidskriftsartikel (refereegranskat)abstract
- Collagen type X is a short, network-forming collagen expressed temporally and spatially tightly controlled in hypertrophic chondrocytes during endochondral ossification. Studies on chicken chondrocytes indicate that the regulation of type X collagen gene expression is regulated at the transcriptional level. In this study, we have analyzed the regulatory elements of the human type X collagen (Col10a1) by reporter gene constructs and transient transfections in chondrogenic and nonchondrogenic cells. Four different promoter fragments covering up to 2,864 bp of 5'-flanking sequences, either including or lacking the first intron, were linked to luciferase reporter gene and transfected into 3T3 fibroblasts, HT1080 fibrosarcoma cells, prehypertrophic chondrocytes from the resting zone, hypertrophic chondrocytes, and chondrogenic cell lines. The results indicated the presence of three regulatory elements in the human Col10a1 gene besides the proximal promoter. First, a negative regulatory element located between 2.4 and 2.8 kb upstream of the transcription initiation site was active in all nonchondrogenic cells and in prehypertrophic chondrocytes. Second, a positive, but also non-tissue-specific positive regulatory element was present in the first intron. Third, a cell-type-specific enhancer element active only in hypertrophic chondrocytes was located between -2.4 and -0.9 kb confirming a previous report by Thomas et al. [(1995): Gene 160:291-296]. The enhancing effect, however, was observed only when calcium phosphate was either used for transfection or included in the culture medium after lipofection. These findings demonstrate that the rigid control of human Col10a1 gene expression is achieved by both positive and negative regulatory elements in the gene and provide the basis for the identification of factors binding to those elements.
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| 4. |
- Wang, Z. Q., et al.
(författare)
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PARP is important for genomic stability but dispensable in apoptosis
- 1997
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Ingår i: Genes & Development. - : Cold Spring Harbor Laboratory Press (CSHL). - 0890-9369 .- 1549-5477. ; 11:18, s. 2347-2358
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Tidskriftsartikel (refereegranskat)abstract
- Mice lacking the gene encoding poly(ADP-ribosyl) transferase (PARP or ADPRT) display no phenotypic abnormalities, although aged mice are susceptible to epidermal hyperplasia and obesity in a mixed genetic background. Whereas embryonic fibroblasts lacking PARP exhibit normal DNA excision repair, they grow more slowly in vitro. Here we investigated the putative roles of PARP in cell proliferation, cell death, radiosensitivity, and DNA recombination, as well as chromosomal stability. We show that the proliferation deficiency in vitro and in vive is most likely caused by a hypersensitive response to environmental stress. Although PARP is specifically cleaved during apoptosis, cells Backing this molecule apoptosed normally in response to treatment with anti-Fas, tumor neurosis factor alpha, gamma-irradiation, and dexamethasone, indicating that PARP is dispensable in apoptosis and that PARP-/-thymocytes are not hypersensitive to ionizing radiation. Furthermore, the capacity of mutant cells to carry out immunoglobulin class switching and V(D)J recombination is normal. Finally, primary PARP mutant fibroblasts and splenocytes exhibited an elevated frequency of spontaneous sister chromatid exchanges and elevated micronuclei formation after treatment with genotoxic agents, establishing an important role for PARP in the maintenance of genomic integrity.
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| 5. |
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| 6. |
- Löfstedt, Christer
(författare)
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Moth pheromone genetics and evolution
- 1993
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Ingår i: Philosophical Transactions of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2970. ; 340:1292, s. 167-177
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Tidskriftsartikel (refereegranskat)abstract
- Argues that there is no reason to dismiss species recognition as a possible cause of evolutionary change in moth sex pheromones. Selection for species recognition cannot explain all of the diversity in sex pheromones and the data supporting this contention are weak, but the alternative causes suggested, invoking mate choice between conspecifics as the mechanism of sexual selection, has no empirical support. Finding and analysing genes responsible for mate choice is important to corroborate any theory of sexual selection and speciation, and genetic dissection of moth pheromone communication has provided important progress. Mendelian genes controlling differences in mate choice and in the production of mate recognition signals have been found. -from Author
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| 7. |
- Löfstedt, Christer
(författare)
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Population variation and genetic control of pheromone communication systems in moths
- 1990
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Ingår i: Entomologia Experimentalis et Applicata. - : Wiley. - 0013-8703. ; 54:3, s. 199-218
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Forskningsöversikt (refereegranskat)abstract
- The nature of variation in moth pheromone communication systems and its genetic control is critical for the evolution of these systems and for their role in mate‐finding and reproductive isolation. Significant additive genetic variance has been demonstrated in female pheromone production in monomorphic populations. However, corresponding variance in male pheromone response with respect to the blend which is most active, appears to be low, as can be expected from the general asymmetry of sexual selection. Pheromone polymorphism and differences in communication systems between closely related species seem to be controlled by a small number of Mendelian genes. The critical biosynthetic steps, which are influenced by the genes controlling pheromone production, can be inferred from our present knowledge of pheromone biosynthesis. A mechanistic understanding of how male response to pheromones is controlled is further away. Failure to demonstrate genes with pleiotropic effects on critical sender and receiver traits, suggests that reciprocal selection on genetically independent sender and receiver loci is the more likely explanation for the generally observed coordination between pheromone production and response in moth populations. Further research on the evolutionary significance of Z‐linked pheromone response genes, documented in several species, should be encouraged. Investigations, in the field, of populations that vary in pheromone production and response, and theoretical and empirical studies of the survival of sender and receiver mutants in otherwise monomorphic populations are also important to advance our understanding of how pheromone communication systems evolve. 1990 The Netherlands Entomological Society
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| 8. |
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| 9. |
- Andersson, Helene
(författare)
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Mitochondrial plasmids, genetic conflicts and sex-determination in Silene vulgaris
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plants like all other eukaryotic organisms carry most of their DNA in the nucleus. In addition, plants also have both chloroplasts and mitochondria that contain their own genetic material. The genomes in chloroplasts and mitochondria control certain vital processes, but most often the organelles act under strict nuclear control. Usually the nuclear and organellar genomes live in "harmony", promoting themselves by helping each other. The mitochondrial and nuclear genomes can, however, sometimes end up in a conflict of interest. Cytoplasmic male sterility, is an example, where such a conflict may arise; in this case over the sexual development of carrier plants. A factor complicating the organization and control of the genetic material in plants even more, is the existence of mitochondrial plasmids. Mitochondrial plasmids have been reported to show deviations from strict maternal inheritance and to have effects on the sexual development of their carriers. These extrachromosomal genetic elements can be regarded as a third level of genome organization. In plants carrying mitochondrial plasmids conflicts of interest are therefore possible between three genetic actors: the chromosomes in the nucleus, the mitochondrial genome, and the plasmid DNA/RNA. Theoretical models were set up to extend our understanding of how such conflicts can develop and to study which parameters are of importance for the spread and maintenance of mitochondrial plasmids in plant populations. They show that some degree of paternal transmission via pollen is important for the spread of mitochondrial plasmids. The analyses also show that the most likely long-term evolutionary direction is towards plasmids with weak phenotypic effects and a strict maternal mode of transmission. To investigate the parameters for plasmid spread and evolution, we chose to study the naturally occurring weed Silene vulgaris, the bladder campion, a member of the Caryophyllaceae family, which carries mitochondrial plasmids. Three different length variants of mitochondrial plasmids of S. vulgaris could be recognized and they were distributed among populations over the whole investigated area of Skåne, the southernmost county of Sweden. The plasmids of S. vulgaris show no deviation from strict maternal inheritance. Neither were any effects detected on their host plants? fitness or sexual development that could be separated from effects caused by the background cytoplasm. The mitochondrial plasmids of S. vulgaris seem to have reached a state of almost perfect maternal transmission and of weak phenotypic effects, as predicted by the models. The existence of male sterility in S. vulgaris cannot be explained by the occurrence of mitochondrial plasmids. However, there is evidence for both cytoplasmic and nuclear genes being involved in sex-determination. In S. vulgaris, as in several other gynodioecious species, so called gynomonoecious (i.e. partially male sterile) individuals are sometimes found. The standard explanation for the occurrence of this third gender is incomplete nuclear restoration of male-sterilizing cytoplasms. Here, an alternative interpretation is given to partial male sterility in S. vulgaris: Heteroplasmy of factors involved in sexual development can produce the mosaic of flowers found in gynomonoecious plants, as well as the differences in gender proportions among offspring from flowers of different types on a single plant.
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| 10. |
- Appelgren, Henrik, 1965-
(författare)
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Spontaneous and induced mutations at the human minisatellite MS32 in yeast
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tandem repetitive DNA including minisatellites make up a large part of eukaryotic genomes, and some tandem repetitive loci are associated with human disease. Little is known about the functions and dynamics of these sequences. Hypervariable minisatellites are used as naturally occurring genetic markers and form the basis of DNA fingerprinting. Studies in human have shown that minisatellite alleles frequently mutate to new lengths by recombination-based mechanisms that operate in the germline, possibly in meiosis. In addition to the variability in length, all hypervariable minisatellites characterised to date also show variation in the DNA sequence of repeat units. The order of variant repeat units can be revealed by MVR-PCR (Minisatellite Variant Repeat mapping by PCR), and this has greatly contributed to mutation analysis by comparing structures of alleles before and after mutation. Certain aspects of minisatellite mutation and general eukaryotic meiotic recombination, cannot be studies in human or any other mammalian system. It was therefore necessary to develop a manipulable eukaryotic model system in the yeast Saccharomyces cerevisiae. The best characterised human minisatellite MS32 was integrated in the vicinity of a hotspot for meiotic recombination in chromosome III. This thesis presents the construction of the model system and analyses of MS32 mutation in yeast.The results proved that MS32 mutation is induced in meiosis. Mutant structures were strikingly similar to mutant structures seen in man. Tetrad analysis demonstrated that gene conversion is the major pathway leading to interallelic exchanges. The data also suggested that a hyper-recombinogenic state is formed, and it was shown that entire alleles can be transferred from a chromatid to another. An allele that displays reduced mutation rate in man showed a reduced mutation rate also in yeast. The results have implications for general eukaryotic meiotic recombination. Mutations at MS32 were induced in meiosis by PCB, suggesting that the model system can be used as an in vitro bioassay for the screening of environmental contaminants capable of inducing genomic damage in meiosis. It is concluded that the yeast model constitute a suitable system for the molecular dissection of pathways in spontaneous and induced minisatellite mutations and for elucidating general eukaryotic meiotic recombination mechanisms.
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