The Enamelin Genes in Lizard, Crocodile, and Frog and the Pseudogene in the Chicken Provide New Insights on Enamelin Evolution in Tetrapods
The Enamelin Genes in Lizard, Crocodile, and Frog and the Pseudogene in the Chicken Provide New Insights on Enamelin Evolution in Tetrapods
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DOI：
10.1093/molbev/msq098
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发表时间：
2010-09-01
影响因子：
10.7
通讯作者：
Sire, Jean-Yves
中科院分区：
文献类型：
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作者：
Al-Hashimi, Nawfal;Lafont, Anne-Gaelle;Sire, Jean-Yves
釉蛋白（Enamelin，ENAM）是釉质形成和矿化的重要蛋白质。以前的分子分析表明，可能起源于脊椎动物进化的早期，这是由早期脊椎动物中的釉质/釉质样组织的存在支持。与这些假设相反，ENAM仅在哺乳动物中被表征。我们的目标是1）在非哺乳动物四足动物的代表中寻找ENAM，2）在鸡基因组中寻找假基因，3）看看新序列是否能带来关于ENAM进化的新信息。使用在硅片上的方法和聚合酶链反应，我们获得和表征的信使RNA序列的ENAM在青蛙，蜥蜴，鳄鱼;基因组DNA序列的ENAM在青蛙和蜥蜴;和推定的序列鸡ENAM假基因。与哺乳动物ENAM序列的比较表明：1）蜥脚类和有袋类存在一个额外的编码外显子，命名为外显子8b，2）非哺乳动物ENAM中存在一个简单的5 '非翻译区，3）大外显子中存在许多序列变异，而小外显子中存在一些保守区域，和4）25种氨基酸在3.5亿年的四足动物进化过程中保持不变，因此具有重要的生物学意义。在考虑哺乳动物的基因同线性时没有预料到的区域中鉴定出鸡假基因。加上蜥蜴ENAM在同源区域的位置，这一结果表明，釉质基因可能是易位在蜥脚类动物血统的祖先。这项研究支持了ENAM在脊椎动物进化早期的起源，证实了现代鸟类的牙齿缺失导致了釉质基因的失效，并增加了关于磷酸化丝氨酸和糖基化天冬酰胺对正确的ENAM功能所起的重要作用的信息。
Enamelin (ENAM) has been shown to be a crucial protein for enamel formation and mineralization. Previous molecular analyses have indicated a probable origin early in vertebrate evolution, which is supported by the presence of enamel/enameloid tissues in early vertebrates. In contrast to these hypotheses, ENAM was only characterized in mammals. Our aims were to 1) look for ENAM in representatives of nonmammalian tetrapods, 2) search for a pseudogene in the chicken genome, and 3) see whether the new sequences could bring new information on ENAM evolution. Using in silico approach and polymerase chain reaction, we obtained and characterized the messenger RNA sequences of ENAM in a frog, a lizard, and a crocodile; the genomic DNA sequences of ENAM in a frog and a lizard; and the putative sequence of chicken ENAM pseudogene. The comparison with mammalian ENAM sequences has revealed 1) the presence of an additional coding exon, named exon 8b, in sauropsids and marsupials, 2) a simpler 5'-untranslated region in nonmammalian ENAMs, 3) many sequence variations in the large exons while there are a few conserved regions in small exons, and 4) 25 amino acids that have been conserved during 350 million years of tetrapod evolution and hence of crucial biological importance. The chicken pseudogene was identified in a region that was not expected when considering the gene synteny in mammals. Together with the location of lizard ENAM in a homologous region, this result indicates that enamel genes were probably translocated in an ancestor of the sauropsid lineage. This study supports the origin of ENAM earlier in vertebrate evolution, confirms that tooth loss in modern birds led to the invalidation of enamel genes, and adds information on the important role played by, for example, the phosphorylated serines and the glycosylated asparagines for correct ENAM functions.