Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales
Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales
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DOI：
10.1098/rspb.2010.1280
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发表时间：
2011-04-07
影响因子：
4.7
通讯作者：
Springer, Mark S.
中科院分区：
文献类型：
--
作者：
Meredith, Robert W.;Gatesy, John;Springer, Mark S.
须鲸亚目的鲸鱼是滤食动物，它们用鲸须从海洋沃茨中筛选浮游动物和小鱼。成年后的密齿龙没有牙齿，但在胚胎阶段就有牙芽。支序分析表明，冠群Mysticeti的共同祖先失去了功能性牙齿。牙齿特异性基因成釉蛋白（AMBN）、釉蛋白（ENAM）和釉原蛋白（AMEL）的DNA序列在该分类群中具有移码突变和/或终止密码子，但这些分子空腔中没有一个是所有现存的神秘生物所共有的。在这里，我们提供了牙齿基因，釉质溶素（MMP 20），在生活须鲸的共同祖先的伪基因化的第一个证据。具体地说，假基因化是由于MMP 20外显子2中插入了一个α-2 SINE逆转录子所致。基因组和古生物学数据现在提供了一致的支持，在共同的祖先分支冠组mysticopia的釉质覆盖的牙齿的损失。MMP 20的新数据还证明了侏儒抹香鲸（Kogia breviceps）外显子2中的多态终止密码子，它的牙齿没有釉质。这些结果，结合证据的假基因化的MMP 20在霍夫曼的两趾树懒（Choloepus hoffmanni），另一种无釉物种，支持的假设，唯一独特的，非重叠功能的MMP 20基因是在釉质形成。
Whales in the suborder Mysticeti are filter feeders that use baleen to sift zooplankton and small fish from ocean waters. Adult mysticetes lack teeth, although tooth buds are present in foetal stages. Cladistic analyses suggest that functional teeth were lost in the common ancestor of crown-group Mysticeti. DNA sequences for the tooth-specific genes, ameloblastin (AMBN), enamelin (ENAM) and amelogenin (AMEL), have frameshift mutations and/or stop codons in this taxon, but none of these molecular cavities are shared by all extant mysticetes. Here, we provide the first evidence for pseudogenization of a tooth gene, enamelysin (MMP20), in the common ancestor of living baleen whales. Specifically, pseudogenization resulted from the insertion of a CHR-2 SINE retroposon in exon 2 of MMP20. Genomic and palaeontological data now provide congruent support for the loss of enamel-capped teeth on the common ancestral branch of crown-group mysticetes. The new data for MMP20 also document a polymorphic stop codon in exon 2 of the pygmy sperm whale (Kogia breviceps), which has enamel-less teeth. These results, in conjunction with the evidence for pseudogenization of MMP20 in Hoffmann's two-toed sloth (Choloepus hoffmanni), another enamel-less species, support the hypothesis that the only unique, non-overlapping function of the MMP20 gene is in enamel formation.