Biology Department, Unit of Ecology and Systematics, Amphibian Evolution Lab, Vrije Universiteit Brussel, Brussels, Belgium.
Mol Biol Evol. 2012 Mar;29(3):995-1004. doi: 10.1093/molbev/msr269. Epub 2011 Oct 31.
The conquest of land was arguably one of the most fundamental ecological transitions in vertebrates and entailed significant changes in skin structure and appendages to cope with the new environment. In extant tetrapods, the rigidity of the integument is largely created by type I and type II keratins, which are structural proteins essential in forming a strong cytoplasmic network. It is expected that such proteins have undergone fundamental changes in both stem and crown tetrapods. Here, we integrate genomic, phylogenetic, and expression data in a comprehensive study on the early evolution and functional diversification of tetrapod keratins. Our analyses reveal that all type I and type II tetrapod keratins evolved from only two genes that were present in the ancestor of extant vertebrates. Subsequently, the water-to-land transition in the stem lineage of tetrapods was associated with a major radiation and functional diversification of keratin genes. These duplications acquired functions that serve rigidity in integumental hard structures and were the prime for subsequent independent keratin diversification in tetrapod lineages.
陆地征服可以说是脊椎动物中最基本的生态转变之一，需要皮肤结构和附属物发生重大变化，以适应新环境。在现存的四足动物中，表皮的刚性主要是由 I 型和 II 型角蛋白形成的，角蛋白是形成强大细胞质网络的必需结构蛋白。预计这种蛋白质在四足动物的茎干和冠群中都发生了根本变化。在这里，我们将基因组、系统发育和表达数据整合在一项关于四足动物角蛋白早期进化和功能多样化的综合研究中。我们的分析表明，所有的 I 型和 II 型四足动物角蛋白都由现存脊椎动物祖先中存在的两个基因进化而来。随后，四足动物的茎干谱系向水到陆的转变与角蛋白基因的主要辐射和功能多样化有关。这些基因的复制获得了在表皮硬结构中保持刚性的功能，这是四足动物谱系中随后独立角蛋白多样化的主要原因。
