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钟鸣
(2023-06-30 22:31):
#paper doi：10.1093/molbev/msad102 Caecilian Genomes Reveal the Molecular Basis of Adaptation and Convergent Evolution of Limblessness in Snakes and Caecilians
这是一篇比较基因组阐释进化问题的论文，比较的是蚓螈与蛇的基因组的共同特征，因为二者趋同进化至无足。作者分析了4个内容：重复区域分析、基因家族分析、正选择基因分析、ZRS增强子损失分析。分析结果集中于2点，第一点是这两个物种的基因组的 69% 以上都是由重复区域组成，其中逆转录转座子最为丰富。第二个发现是蚓螈的ZRS基因的增强子区域发生了缺失，这个基因在蛇中发生了突变，且该突变基因导入小鼠后会产生蛇样突变。这组证据强烈暗示该基因与无足表型的关联。
Abstract:
We present genome sequences for the caecilians Geotrypetes seraphini (3.8 Gb) and Microcaecilia unicolor (4.7 Gb), representatives of a limbless, mostly soil-dwelling amphibian clade with reduced eyes, and unique putatively …
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We present genome sequences for the caecilians Geotrypetes seraphini (3.8 Gb) and Microcaecilia unicolor (4.7 Gb), representatives of a limbless, mostly soil-dwelling amphibian clade with reduced eyes, and unique putatively chemosensory tentacles. More than 69% of both genomes are composed of repeats, with retrotransposons being the most abundant. We identify 1,150 orthogroups that are unique to caecilians and enriched for functions in olfaction and detection of chemical signals. There are 379 orthogroups with signatures of positive selection on caecilian lineages with roles in organ development and morphogenesis, sensory perception, and immunity amongst others. We discover that caecilian genomes are missing the zone of polarizing activity regulatorysequence (ZRS) enhancer of Sonic Hedgehog which is also mutated in snakes. In vivo deletions have shown ZRS is required for limb development in mice, thus, revealing a shared molecular target implicated in the independent evolution of limblessness in snakes and caecilians.
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