Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
Department of Biology, University of Texas at Tyler, Tyler, TX 75799, USA.
Genes (Basel). 2021 May 18;12(5):767. doi: 10.3390/genes12050767.
The transition of amniotes to a fully terrestrial lifestyle involved the adaptation of major molecular innovations to the epidermis, often in the form of epidermal appendages such as hair, scales and feathers. Feathers are diverse epidermal structures of birds, and their evolution has played a key role in the expansion of avian species to a wide range of lifestyles and habitats. As with other epidermal appendages, feather development is a complex process which involves many different genetic and protein elements. In mammals, many of the genetic elements involved in epidermal development are located at a specific genetic locus known as the epidermal differentiation complex (EDC). Studies have identified a homologous EDC locus in birds, which contains several genes expressed throughout epidermal and feather development. A family of avian EDC genes rich in aromatic amino acids that also contain MTF amino acid motifs (EDAAs/EDMTFs), that includes the previously reported histidine-rich or fast-protein (HRP/fp), an important marker in feather development, has expanded significantly in birds. Here, we characterize the EDAA gene family in birds and investigate the evolutionary history and possible functions of EDAA genes using phylogenetic and sequence analyses. We provide evidence that the EDAA gene family originated in an early archosaur ancestor, and has since expanded in birds, crocodiles and turtles, respectively. Furthermore, this study shows that the respective amino acid compositions of avian EDAAs are characteristic of structural functions associated with EDC genes and feather development. Finally, these results support the hypothesis that the genes of the EDC have evolved through tandem duplication and diversification, which has contributed to the evolution of the intricate avian epidermis and epidermal appendages.
羊膜动物向完全陆生生活方式的转变涉及主要分子创新适应表皮，通常以表皮附属物的形式，如毛发、鳞片和羽毛。羽毛是鸟类多样化的表皮结构，它们的进化在鸟类物种向广泛的生活方式和栖息地的扩张中发挥了关键作用。与其他表皮附属物一样，羽毛发育是一个复杂的过程，涉及许多不同的遗传和蛋白质元素。在哺乳动物中，许多参与表皮发育的遗传元素位于一个特定的遗传基因座，称为表皮分化复合物（EDC）。研究已经在鸟类中鉴定出了一个同源的 EDC 基因座，其中包含几个在表皮和羽毛发育过程中表达的基因。鸟类 EDC 基因家族富含芳香族氨基酸，还含有 MTF 氨基酸基序（EDAAs/EDMTFs），其中包括以前报道的富含组氨酸或快速蛋白（HRP/fp），这是羽毛发育的一个重要标志，在鸟类中显著扩张。在这里，我们描述了鸟类的 EDAA 基因家族，并通过系统发育和序列分析研究了 EDAA 基因的进化历史和可能的功能。我们提供的证据表明，EDAA 基因家族起源于早期的恐龙祖先，此后在鸟类、鳄鱼和海龟中分别扩张。此外，这项研究表明，鸟类 EDAAs 的各自氨基酸组成是与 EDC 基因和羽毛发育相关的结构功能的特征。最后，这些结果支持了 EDC 基因通过串联重复和多样化进化的假说，这有助于复杂的鸟类表皮和表皮附属物的进化。
