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  • 1
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    Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-07-23
    Description: Loss of sexual reproduction is considered an evolutionary dead end for metazoans, but bdelloid rotifers challenge this view as they appear to have persisted asexually for millions of years. Neither male sex organs nor meiosis have ever been observed in these microscopic animals: oocytes are formed through mitotic divisions, with no reduction of chromosome number and no indication of chromosome pairing. However, current evidence does not exclude that they may engage in sex on rare, cryptic occasions. Here we report the genome of a bdelloid rotifer, Adineta vaga (Davis, 1873), and show that its structure is incompatible with conventional meiosis. At gene scale, the genome of A. vaga is tetraploid and comprises both anciently duplicated segments and less divergent allelic regions. However, in contrast to sexual species, the allelic regions are rearranged and sometimes even found on the same chromosome. Such structure does not allow meiotic pairing; instead, we find abundant evidence of gene conversion, which may limit the accumulation of deleterious mutations in the absence of meiosis. Gene families involved in resistance to oxidation, carbohydrate metabolism and defence against transposons are significantly expanded, which may explain why transposable elements cover only 3% of the assembled sequence. Furthermore, 8% of the genes are likely to be of non-metazoan origin and were probably acquired horizontally. This apparent convergence between bdelloids and prokaryotes sheds new light on the evolutionary significance of sex.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Flot, Jean-Francois -- Hespeels, Boris -- Li, Xiang -- Noel, Benjamin -- Arkhipova, Irina -- Danchin, Etienne G J -- Hejnol, Andreas -- Henrissat, Bernard -- Koszul, Romain -- Aury, Jean-Marc -- Barbe, Valerie -- Barthelemy, Roxane-Marie -- Bast, Jens -- Bazykin, Georgii A -- Chabrol, Olivier -- Couloux, Arnaud -- Da Rocha, Martine -- Da Silva, Corinne -- Gladyshev, Eugene -- Gouret, Philippe -- Hallatschek, Oskar -- Hecox-Lea, Bette -- Labadie, Karine -- Lejeune, Benjamin -- Piskurek, Oliver -- Poulain, Julie -- Rodriguez, Fernando -- Ryan, Joseph F -- Vakhrusheva, Olga A -- Wajnberg, Eric -- Wirth, Benedicte -- Yushenova, Irina -- Kellis, Manolis -- Kondrashov, Alexey S -- Mark Welch, David B -- Pontarotti, Pierre -- Weissenbach, Jean -- Wincker, Patrick -- Jaillon, Olivier -- Van Doninck, Karine -- England -- Nature. 2013 Aug 22;500(7463):453-7. doi: 10.1038/nature12326. Epub 2013 Jul 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉University of Namur, Department of Biology, URBE, Laboratory of Evolutionary Genetics and Ecology, 5000 Namur, Belgium. jean-francois.flot@ds.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23873043" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biological Evolution ; Gene Conversion/*genetics ; Gene Transfer, Horizontal/genetics ; Genome/*genetics ; Genomics ; Meiosis/genetics ; Models, Biological ; Reproduction, Asexual/*genetics ; Rotifera/*genetics ; Tetraploidy
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Amphioxus FGF signaling predicts the acquisition of vertebrate morphological traits (2011)
    National Academy of Sciences
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    Publication Date: 2011-05-12
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 3
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    To Tree or Not to Tree? Genome-Wide Quantification of Recombination and Reticulate Evolution during the Diversification of Strict Intracellular Bacteria (2013)
    Oxford University Press
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    Publication Date: 2013-12-11
    Description: It is well known that horizontal gene transfer (HGT) is a major force in the evolution of prokaryotes. During the adaptation of a bacterial population to a new ecological niche, and particularly for intracellular bacteria, selective pressures are shifted and ecological niches reduced, resulting in a lower rate of genetic connectivity. HGT and positive selection are therefore two important evolutionary forces in microbial pathogens that drive adaptation to new hosts. In this study, we use genomic distance analyses, phylogenomic networks, tree topology comparisons, and Bayesian inference methods to investigate to what extent HGT has occurred during the evolution of the genus Rickettsia , the effect of the use of different genomic regions in estimating reticulate evolution and HGT events, and the link of these to host range. We show that ecological specialization restricts recombination occurrence in Rickettsia , but other evolutionary processes and genome architecture are also important for the occurrence of HGT. We found that recombination, genomic rearrangements, and genome conservation all show evidence of network-like evolution at whole-genome scale. We show that reticulation occurred mainly, but not only, during the early Rickettsia radiation, and that core proteome genes of every major functional category have experienced reticulated evolution and possibly HGT. Overall, the evolution of Rickettsia bacteria has been tree-like, with evidence of HGT and reticulated evolution for around 10–25% of the core Rickettsia genome. We present evidence of extensive recombination/incomplete lineage sorting (ILS) during the radiation of the genus, probably linked with the emergence of intracellularity in a wide range of hosts.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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  • 4
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    Amphioxus FGF signaling predicts the acquisition of vertebrate morphological traits [Evolution] (2011)
    National Academy of Sciences
    Details
    Publication Date: 2011-06-01
    Description: FGF signaling is one of the few cell–cell signaling pathways conserved among all metazoans. The diversity of FGF gene content among different phyla suggests that evolution of FGF signaling may have participated in generating the current variety of animal forms. Vertebrates possess the greatest number of FGF genes, the functional evolution of which may have been implicated in the acquisition of vertebrate-specific morphological traits. In this study, we have investigated the roles of the FGF signal during embryogenesis of the cephalochordate amphioxus, the best proxy for the chordate ancestor. We first isolate the full FGF gene complement and determine the evolutionary relationships between amphioxus and vertebrate FGFs via phylogenetic and synteny conservation analysis. Using pharmacological treatments, we inhibit the FGF signaling pathway in amphioxus embryos in different time windows. Our results show that the requirement for FGF signaling during gastrulation is a conserved character among chordates, whereas this signal is not necessary for neural induction in amphioxus, in contrast to what is known in vertebrates. We also show that FGF signal, acting through the MAPK pathway, is necessary for the formation of the most anterior somites in amphioxus, whereas more posterior somite formation is not FGF-dependent. This result leads us to propose that modification of the FGF signal function in the anterior paraxial mesoderm in an amphioxus-like vertebrate ancestor might have contributed to the loss of segmentation in the preotic paraxial mesoderm of the vertebrate head.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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