Strasser Bettina, Mlitz Veronika, Hermann Marcela, Tschachler Erwin, Eckhart Leopold
Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Lazarettgasse 14, 1090, Vienna, Austria.
Department of Medical Biochemistry, Medical University of Vienna, Vienna, Austria.
BMC Evol Biol. 2015 May 7;15:82. doi: 10.1186/s12862-015-0360-y.
Feathers and hair consist of cornified epidermal keratinocytes in which proteins are crosslinked via disulfide bonds between cysteine residues of structural proteins to establish mechanical resilience. Cysteine-rich keratin-associated proteins (KRTAPs) are important components of hair whereas the molecular components of feathers have remained incompletely known. Recently, we have identified a chicken gene, named epidermal differentiation cysteine-rich protein (EDCRP), that encodes a protein with a cysteine content of 36%. Here we have investigated the putative role of EDCRP in the molecular architecture and evolution of feathers.
Comparative genomics showed that the presence of an EDCRP gene and the high cysteine content of the encoded proteins are conserved among birds. Avian EDCRPs contain a species-specific number of sequence repeats with the consensus sequence CCDPCQ(K/Q)(S/P)V, thus resembling mammalian cysteine-rich KRTAPs which also contain sequence repeats of similar sequence. However, differences in gene loci and exon-intron structures suggest that EDCRP and KRTAPs have not evolved from a common gene ancestor but represent the products of convergent sequence evolution. mRNA in situ hybridization demonstrated that chicken EDCRP is expressed in the subperiderm layer of the embryonic epidermis and in the barbule cells of growing feathers. This expression pattern supports the hypothesis that feathers are evolutionarily derived from the subperiderm.
The results of this study suggest that convergent sequence evolution of avian EDCRP and mammalian KRTAPs has contributed to independent evolution of feathers and hair, respectively.
羽毛和毛发由角质化的表皮角质形成细胞组成，其中蛋白质通过结构蛋白半胱氨酸残基之间的二硫键交联，以建立机械弹性。富含半胱氨酸的角蛋白相关蛋白（KRTAPs）是毛发的重要组成部分，而羽毛的分子成分仍不完全清楚。最近，我们鉴定了一个鸡基因，命名为表皮分化富含半胱氨酸蛋白（EDCRP），它编码一种半胱氨酸含量为36%的蛋白质。在此，我们研究了EDCRP在羽毛分子结构和进化中的假定作用。
比较基因组学表明，EDCRP基因的存在以及所编码蛋白质的高半胱氨酸含量在鸟类中是保守的。鸟类EDCRP含有特定物种数量的具有一致序列CCDPCQ(K/Q)(S/P)V的序列重复，因此类似于哺乳动物富含半胱氨酸的KRTAPs，后者也含有相似序列的序列重复。然而，基因座和外显子-内含子结构的差异表明，EDCRP和KRTAPs并非从共同的基因祖先进化而来，而是代表趋同序列进化的产物。mRNA原位杂交表明，鸡EDCRP在胚胎表皮下层和生长羽毛的羽小枝细胞中表达。这种表达模式支持了羽毛在进化上源自表皮下层的假说。
本研究结果表明，鸟类EDCRP和哺乳动物KRTAPs的趋同序列进化分别促进了羽毛和毛发的独立进化。
