Eckhart Leopold, Dalla Valle Luisa, Jaeger Karin, Ballaun Claudia, Szabo Sandra, Nardi Alessia, Buchberger Maria, Hermann Marcela, Alibardi Lorenzo, Tschachler Erwin
Department of Dermatology, Medical University of Vienna, Vienna 1090, Austria.
Proc Natl Acad Sci U S A. 2008 Nov 25;105(47):18419-23. doi: 10.1073/pnas.0805154105. Epub 2008 Nov 10.
The appearance of hair is one of the main evolutionary innovations in the amniote lineage leading to mammals. The main components of mammalian hair are cysteine-rich type I and type II keratins, also known as hard alpha-keratins or "hair keratins." To determine the evolutionary history of these important structural proteins, we compared the genomic loci of the human hair keratin genes with the homologous loci of the chicken and of the green anole lizard Anolis carolinenis. The genome of the chicken contained one type II hair keratin-like gene, and the lizard genome contained two type I and four type II hair keratin-like genes. Orthology of the latter genes and mammalian hair keratins was supported by gene locus synteny, conserved exon-intron organization, and amino acid sequence similarity of the encoded proteins. The lizard hair keratin-like genes were expressed most strongly in the digits, indicating a role in claw formation. In addition, we identified a novel group of reptilian cysteine-rich type I keratins that lack homologues in mammals. Our data show that cysteine-rich alpha-keratins are not restricted to mammals and suggest that the evolution of mammalian hair involved the co-option of pre-existing structural proteins.
毛发的出现是羊膜动物谱系通向哺乳动物过程中的主要进化创新之一。哺乳动物毛发的主要成分是富含半胱氨酸的I型和II型角蛋白，也称为硬α-角蛋白或“毛发角蛋白”。为了确定这些重要结构蛋白的进化史，我们将人类毛发角蛋白基因的基因组位点与鸡和绿安乐蜥（Anolis carolinenis）的同源位点进行了比较。鸡的基因组包含一个II型毛发角蛋白样基因，蜥蜴的基因组包含两个I型和四个II型毛发角蛋白样基因。基因座同线性、保守的外显子-内含子组织以及编码蛋白的氨基酸序列相似性支持了后一类基因与哺乳动物毛发角蛋白的直系同源关系。蜥蜴的毛发角蛋白样基因在趾部表达最强，表明其在爪形成中起作用。此外，我们鉴定出一组新的富含半胱氨酸的I型爬行动物角蛋白，它们在哺乳动物中没有同源物。我们的数据表明，富含半胱氨酸的α-角蛋白并不局限于哺乳动物，并表明哺乳动物毛发的进化涉及对先前存在的结构蛋白的选择利用。
