| 1. |
- Andersson, Jan O, 1971-, et al.
(author)
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A cyanobacterial gene in nonphotosynthetic protists : an early chloroplast acquisition in eukaryotes?
- 2002
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In: Current Biology. - 0960-9822 .- 1879-0445. ; 12:2, s. 115-119
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Journal article (peer-reviewed)abstract
- Since the incorporation of mitochondria and chloroplasts (plastids) into the eukaryotic cell by endosymbiosis, genes have been transferred from the organellar genomes to the nucleus of the host, via an ongoing process known as endosymbiotic gene transfer. Accordingly, in photosynthetic eukaryotes, nuclear genes with cyanobacterial affinity are believed to have originated from endosymbiotic gene transfer from chloroplasts. Analysis of the Arabidopsis thaliana genome has shown that a significant fraction (2%-9%) of the nuclear genes have such an endosymbiotic origin. Recently, it was argued that 6-phosphogluconate dehydrogenase (gnd)-the second enzyme in the oxidative pentose phosphate pathway-was one such example. Here we show that gnd genes with cyanobacterial affinity also are present in several nonphotosynthetic protistan lineages, such as Heterolobosea, Apicomplexa, and parasitic Heterokonta. Current data cannot definitively resolve whether these groups acquired the gnd gene by primary and/or secondary endosymbiosis or via an independent lateral gene transfer event. Nevertheless, our data suggest that chloroplasts were introduced into eukaryotes much earlier than previously thought and that several major groups of heterotrophic eukaryotes have secondarily lost photosynthetic plastids.
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| 2. |
- Andersson, Jan O, 1971-
(author)
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Evolutionary genomics : is Buchnera a bacterium or an organelle?
- 2000
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In: Current Biology. - 0960-9822 .- 1879-0445. ; 10:23, s. R866-R868
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Journal article (peer-reviewed)abstract
- The first genome sequence of an intracellular bacterial symbiont of a eukaryotic cell has been determined. The Buchnera genome shares features with the genomes of both intracellular pathogenic bacteria and eukaryotic organelles, and it may represent an intermediate between the two.
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| 3. |
- Andersson, Jan O, 1971-, et al.
(author)
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Phylogenetic analyses of diplomonad genes reveal frequent lateral gene transfers affecting eukaryotes
- 2003
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In: Current Biology. - 0960-9822 .- 1879-0445. ; 13:2, s. 94-104
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Journal article (peer-reviewed)abstract
- BACKGROUND: Lateral gene transfer (LGT) is an important evolutionary mechanism among prokaryotes. The situation in eukaryotes is less clear; the human genome sequence failed to give strong support for any recent transfers from prokaryotes to vertebrates, yet a number of LGTs from prokaryotes to protists (unicellular eukaryotes) have been documented. Here, we perform a systematic analysis to investigate the impact of LGT on the evolution of diplomonads, a group of anaerobic protists.RESULTS: Phylogenetic analyses of 15 genes present in the genome of the Atlantic Salmon parasite Spironucleus barkhanus and/or the intestinal parasite Giardia lamblia show that most of these genes originated via LGT. Half of the genes are putatively involved in processes related to an anaerobic lifestyle, and this finding suggests that a common ancestor, which most probably was aerobic, of Spironucleus and Giardia adapted to an anaerobic environment in part by acquiring genes via LGT from prokaryotes. The sources of the transferred diplomonad genes are found among all three domains of life, including other eukaryotes. Many of the phylogenetic reconstructions show eukaryotes emerging in several distinct regions of the tree, strongly suggesting that LGT not only involved diplomonads, but also involved other eukaryotic groups.CONCLUSIONS: Our study shows that LGT is a significant evolutionary mechanism among diplomonads in particular and protists in general. These findings provide insights into the evolution of biochemical pathways in early eukaryote evolution and have important implications for studies of eukaryotic genome evolution and organismal relationships. Furthermore, "fusion" hypotheses for the origin of eukaryotes need to be rigorously reexamined in the light of these results.
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| 4. |
- Carlen, M., et al.
(author)
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Functional integration of adult-born neurons
- 2002
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In: Current Biology. - 0960-9822 .- 1879-0445. ; 12:7, s. 606-608
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Journal article (peer-reviewed)abstract
- Over the past decade, it has become clear that neural stem cells in the adult mammalian brain continuously generate new neurons, predominantly in the hippocampus and olfactory bulb [1]. However, the central issue of whether these new neurons participate in functional synaptic circuitry has yet to be resolved. Here, we use virus-based transsynaptic neuronal tracing and c-Fos mapping of odor-induced neuronal activity to demonstrate that neurons generated in the adult functionally integrate into the synaptic circuitry of the brain.
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| 5. |
- Flanagan, J Randall, et al.
(author)
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Prediction precedes control in motor learning
- 2003
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In: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 13:2, s. 146-150, Article Number: PII S0960-9822(03)00007-1
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Journal article (peer-reviewed)abstract
- Skilled motor behavior relies on the brain learning both to control the body and predict the consequences of this control. Prediction turns motor commands into expected sensory consequences, whereas control turns desired consequences into motor commands. To capture this symmetry, the neural processes underlying prediction and control are termed the forward and inverse internal models, respectively. Here, we investigate how these two fundamental processes are related during motor learning. We used an object manipulation task in which subjects learned to move a hand-held object with novel dynamic properties along a prescribed path. We independently and simultaneously measured subjects' ability to control their actions and to predict their consequences. We found different time courses for predictor and controller learning, with prediction being learned far more rapidly than control. In early stages of manipulating the object, subjects could predict the consequences of their actions, as measured by the grip force they used to grasp the object, but could not generate appropriate actions for control, as measured by their hand trajectory. As predicted by several recent theoretical models of sensorimotor control, our results indicate that people can learn to predict the consequences of their actions before they can learn to control their actions.
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| 6. |
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| 7. |
- Holmgren, Claes, et al.
(author)
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CpG methylation regulates the Igf2/H19 insulator
- 2001
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In: Current Biology. - 0960-9822 .- 1879-0445. ; 11:14, s. 1128-1130
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Journal article (peer-reviewed)abstract
- The differentially methylated 5'-flank of the mouse H19 gene unidirectionally regulates the communication between enhancer elements and gene promoters and presumably represses maternal Igf2 expression in vivo [1-6]. The specific activation of the paternally inherited Igf2 allele has been proposed to involve methylation-mediated inactivation of the H19 insulator function during male germline development [1-4, 6]. Here, we addressed the role of methylation by inserting a methylated fragment of the H19-imprinting control region (ICR) into a nonmethylated episomal H19 minigene construct, followed by the transfection of ligation mixture into Hep3B cells. Individual clones were expanded and analyzed for genotype, methylation status, chromatin conformation, and insulator function. The results show that the methylated status of the H19 ICR could be propagated for several passages without spreading into the episomal vector. Moreover, the nuclease hypersensitive sites, which are typical for the maternally inherited H19 ICR allele [1], were absent on the methylated ICR, underscoring the suggestion that the methylation mark dictates parent of origin-specific chromatin conformations [1] that involve CTCF [2]. Finally, the insulator function was strongly attenuated in stably maintained episomes. Collectively, these results provide the first experimental support that the H19 insulator function is regulated by CpG methylation.
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| 8. |
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| 9. |
- Norlin, Marianne, et al.
(author)
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Vomeronasal Phenotype and Behavioral Alterations in Gαi2 Mutant Mice
- 2003
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In: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 13:14, s. 1214-1219
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Journal article (peer-reviewed)abstract
- Several social and reproductive behaviors are under the influence of the vomeronasal (VN) organ; VN neurons detect odorous molecules emitted by individuals of the same species. There are two types of VN neurons, and these differ in their expression of chemosensory receptors and G protein subunits. The significance of this dichotomy is largely unknown. VN neurons express high levels of either G alpha i2 or G alpha o. A mouse line carrying a targeted disruption of the G alpha i2 gene offered the opportunity for studying the effects of a lack of receptor signaling through the heterotrimeric Gi2 protein in one VN cell type. As a consequence of this deficiency, the number of VN neurons that normally express G alpha i2 is decreased by half. These residual neurons are defective in eliciting a response in their target neurons in the accessory olfactory bulb. Moreover, G alpha i2 mutant mice show alterations in behaviors for which an intact VN organ is known to be important. Display of maternal aggressive behavior is severely blunted, and male mice show significantly less aggression toward an intruder. However, male mice show unaltered sexual-partner preference. This suggests that the two types of VN neurons may have separate functions in mediating behavioral changes in response to chemosensory information.
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| 10. |
- Silverstein, Rebecka A., et al.
(author)
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A new role for the transcriptional corepressor SIN3; Regulation of centromeres
- 2003
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In: Current Biology. - 0960-9822 .- 1879-0445. ; 13:1, s. 68-72
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Journal article (peer-reviewed)abstract
- Centromeres play a vital role in maintaining the genomic stability of eukaryotes by coordinating the equal distribution of chromosomes to daughter cells during mitosis and meiosis. Fission yeast (S. pombe) centromeres consist of a 4-9 kb central core region and 30-100 kb of flanking inner (imr/B) and outer (otr/K) repeats [1-3]. These sequences direct a laminar kinetochore structure similar to that of human centromeres [4, 5]. Centromeric heterochromatin is generally underacetylated [6, 7]. We have previously shown that inhibition of histone deacetylases (HDACs) caused hyperacetylation of centromeres and defective chromosome segregation [8]. SIN3 is a HDAC corepressor that has the ability to mediate HDAC targeting in the repression of promoters. In this study, we have characterized S. pombe sin three corepressors (Pst1p and Pst2p) to investigate whether SIN3-HDAC is required in the regulation of centromeres. We show that only pst1-1 and not pst2Delta cells displayed anaphase defects and thiabendazole sensitivity. pst1-1 cells showed reduced centromeric silencing, increased histone acetylation in centromeric chromatin, and defective centromeric sister chromatid cohesion. The HDAC Clr6p and Pst1p coimmunoprecipitated, and Pst1p colocalized with centromeres, particularly in binucleate cells. These data are consistent with a model in which Pst1 pClr6p temporally associate with centromeres to carry out the initial deacetylation necessary for subsequent steps in heterochromatin formation.
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