Molecular decay of the tooth gene Enamelin (ENAM) mirrors the loss of enamel in the fossil record of placental mammals.
Molecular decay of the tooth gene Enamelin (ENAM) mirrors the loss of enamel in the fossil record of placental mammals.
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DOI：
10.1371/journal.pgen.1000634
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发表时间：
2009-09
期刊：
影响因子：
4.5
通讯作者：
Springer MS
中科院分区：
文献类型：
--
作者：
Meredith RW;Gatesy J;Murphy WJ;Ryder OA;Springer MS
退化结构在解剖学和分子水平上都有发生，但在化石记录中记录形态退化和基因组中分子衰变同时发生的研究很少。在此，我们利用形态学、化石记录和系统发育预测了4个不同目的胎盘哺乳动物（管齿目、海豚目、鲸目、Xenarthra）中珐琅素（ENAM）基因“分子化石”的发生。我们的研究结果支持“分子化石”假说，并证明移码突变和/或停止密码子在所有无牙和无釉质分类群中都存在。然后，我们使用了一种基于密码子选择强度估计（ω）的新方法来计算食蚁兽和穿山甲化石记录中迭代牙釉质丢失的时间，并进一步表明，尽管移码突变在现存的异种动物的ENAM序列中普遍存在，但ENAM的分子进化史预测了异种动物（树懒、食蚁兽、犰狳）的基础代表中牙釉质的发生。ENAM的分子衰变与胎盘哺乳动物化石记录中牙釉质的形态退化相似，为达尔文理论的预测能力提供了明显的证据。牙釉质是脊椎动物体内最坚硬的物质。珐琅质是珐琅质形成的关键蛋白质之一。大多数胎盘哺乳动物的牙齿都覆盖着牙釉质，但也有没有牙齿的血统（食蚁兽、穿山甲、须鲸）或没有牙釉质的牙齿（犰狳、树懒、食蚁兽、侏儒和侏儒抹香鲸）。所有没有牙齿和珐琅质的哺乳动物都是从有珐琅质牙齿的祖先进化而来的。考虑到这种祖先，我们预测没有牙齿或牙齿缺乏牙釉质的哺乳动物物种会有编码珐琅质蛋白的基因拷贝，但这些物种的珐琅质基因会包含突变，使其成为无功能的假基因。为了验证这一假设，我们对所有缺牙或无牙的胎盘哺乳动物的牙釉质基因的大部分蛋白质编码区域进行了测序。在每种情况下，我们都发现了瓷釉素基因的突变，这些突变破坏了编码瓷釉素蛋白的正确阅读框。我们的研究结果将分子水平上的进化变化与化石记录中的形态变化联系起来，并为查尔斯·达尔文的变异血统理论的巨大预测能力提供了证据。
Vestigial structures occur at both the anatomical and molecular levels, but studies documenting the co-occurrence of morphological degeneration in the fossil record and molecular decay in the genome are rare. Here, we use morphology, the fossil record, and phylogenetics to predict the occurrence of “molecular fossils” of the enamelin (ENAM) gene in four different orders of placental mammals (Tubulidentata, Pholidota, Cetacea, Xenarthra) with toothless and/or enamelless taxa. Our results support the “molecular fossil” hypothesis and demonstrate the occurrence of frameshift mutations and/or stop codons in all toothless and enamelless taxa. We then use a novel method based on selection intensity estimates for codons (ω) to calculate the timing of iterated enamel loss in the fossil record of aardvarks and pangolins, and further show that the molecular evolutionary history of ENAM predicts the occurrence of enamel in basal representatives of Xenarthra (sloths, anteaters, armadillos) even though frameshift mutations are ubiquitous in ENAM sequences of living xenarthrans. The molecular decay of ENAM parallels the morphological degeneration of enamel in the fossil record of placental mammals and provides manifest evidence for the predictive power of Darwin's theory. Enamel is the hardest substance in the vertebrate body. One of the key proteins involved in enamel formation is enamelin. Most placental mammals have teeth that are capped with enamel, but there are also lineages without teeth (anteaters, pangolins, baleen whales) or with enamelless teeth (armadillos, sloths, aardvarks, pygmy and dwarf sperm whales). All toothless and enamelless mammals are descended from ancestral forms that possessed teeth with enamel. Given this ancestry, we predicted that mammalian species without teeth or with teeth that lack enamel would have copies of the gene that codes for the enamelin protein, but that the enamelin gene in these species would contain mutations that render it a nonfunctional pseudogene. To test this hypothesis, we sequenced most of the protein-coding region of the enamelin gene in all groups of placental mammals that lack teeth or have enamelless teeth. In every case, we discovered mutations in the enamelin gene that disrupt the proper reading frame that codes for the enamelin protein. Our results link evolutionary change at the molecular level to morphological change in the fossil record and also provide evidence for the enormous predictive power of Charles Darwin's theory of descent with modification.
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影响因子：
3.4
作者：
Delsuc F;Vizcaíno SF;Douzery EJ
通讯作者：
Douzery EJ
影响因子：
2.7
作者：
Hu, Jan C. -C.;Chun, Yong-Hee P.;Simmer, James P.
通讯作者：
Simmer, James P.
DOI：
10.1073/pnas.0638023100
发表时间：
2003-04-01
影响因子：
11.1
作者：
Kawasaki, K;Weiss, KM
通讯作者：
Weiss, KM
影响因子：
3
作者：
Bollback JP
通讯作者：
Bollback JP
影响因子：
3
作者：
Hart, PS;Michalec, MD;Wright, JT
通讯作者：
Wright, JT