Skin Biology Laboratory, Department of Dermatology, Medical University of Vienna, Vienna, Austria.
Sci Rep. 2022 Aug 10;12(1):13634. doi: 10.1038/s41598-022-18053-7.
The epidermal differentiation complex (EDC) is a cluster of genes encoding components of the skin barrier in terrestrial vertebrates. EDC genes can be categorized as S100 fused-type protein (SFTP) genes such as filaggrin, which contain two coding exons, and single-coding-exon EDC (SEDC) genes such as loricrin. SFTPs are known to be present in amniotes (mammals, reptiles and birds) and amphibians, whereas SEDCs have not yet been reported in amphibians. Here, we show that caecilians (Amphibia: Gymnophiona) have both SFTP and SEDC genes. Two to four SEDC genes were identified in the genomes of Rhinatrema bivittatum, Microcaecilia unicolor and Geotrypetes seraphini. Comparative analysis of tissue transcriptomes indicated predominant expression of SEDC genes in the skin of caecilians. The proteins encoded by caecilian SEDC genes resemble human SEDC proteins, such as involucrin and small proline-rich proteins, with regard to low sequence complexity and high contents of proline, glutamine and lysine. Our data reveal diversification of EDC genes in amphibians and suggest that SEDC-type skin barrier genes have originated either in a common ancestor of tetrapods followed by loss in Batrachia (frogs and salamanders) or, by convergent evolution, in caecilians and amniotes.
表皮分化复合体（EDC）是一个编码陆地脊椎动物皮肤屏障成分的基因簇。EDC 基因可分为 S100 融合型蛋白（SFTP）基因，如含有两个编码外显子的丝聚合蛋白，和单编码exon 的 EDC（SEDC）基因，如兜甲蛋白。SFTP 已知存在于羊膜动物（哺乳动物、爬行动物和鸟类）和两栖动物中，而 SEDC 尚未在两栖动物中报道。在这里，我们表明蚓螈（两栖动物：蚓螈目）具有 SFTP 和 SEDC 基因。在双带鱼螈、双色蚓螈和高山蚓螈的基因组中鉴定出 2 到 4 个 SEDC 基因。组织转录组的比较分析表明，SEDC 基因在蚓螈的皮肤中表达占优势。蚓螈 SEDC 基因编码的蛋白质在序列复杂性低和脯氨酸、谷氨酰胺和赖氨酸含量高方面与人类 SEDC 蛋白质（如兜甲蛋白和小富含脯氨酸蛋白）相似。我们的数据揭示了两栖动物 EDC 基因的多样化，并表明 SEDC 型皮肤屏障基因要么起源于四足动物的共同祖先，随后在两栖动物（青蛙和蝾螈）中丢失，要么通过趋同进化在蚓螈和羊膜动物中产生。
