Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA.
Bell Museum of Natural History, University of Minnesota, Saint Paul, MN 55113, USA.
Integr Comp Biol. 2019 Jul 1;59(1):193-202. doi: 10.1093/icb/icz010.
Corneous proteins are an important component of the tetrapod integument. Duplication and diversification of keratins and associated proteins are linked with the origin of most novel integumentary structures like mammalian hair, avian feathers, and scutes covering turtle shells. Accordingly, the loss of integumentary structures often coincides with the loss of genes encoding keratin and associated proteins. For example, many hair keratins in dolphins and whales have become pseudogenes. The adhesive setae of geckos and anoles are composed of both intermediate filament keratins (IF-keratins, formerly known as alpha-keratins) and corneous beta-proteins (CBPs, formerly known as beta-keratins) and recent whole genome assemblies of two gecko species and an anole uncovered duplications in seta-specific CBPs in each of these lineages. While anoles evolved adhesive toepads just once, there are two competing hypotheses about the origin(s) of digital adhesion in geckos involving either a single origin or multiple origins. Using data from three published gecko genomes, I examine CBP gene evolution in geckos and find support for a hypothesis where CBP gene duplications are associated with the repeated evolution of digital adhesion. Although these results are preliminary, I discuss how additional gecko genome assemblies, combined with phylogenies of keratin and associated protein genes and gene duplication models, can provide rigorous tests of several hypotheses related to gecko CBP evolution. This includes a taxon sampling strategy for sequencing and assembly of gecko genomes that could help resolve competing hypotheses surrounding the origin(s) of digital adhesion.
角蛋白和相关蛋白的复制和多样化与大多数新型表皮结构的起源有关，如哺乳动物的毛发、鸟类的羽毛和覆盖海龟壳的鳞片。因此，表皮结构的丧失通常与编码角蛋白和相关蛋白的基因的丧失同时发生。例如，海豚和鲸鱼的许多毛发角蛋白已成为假基因。壁虎和变色龙的粘性刚毛由中间丝角蛋白（IF-角蛋白，以前称为α-角蛋白）和角蛋白β-蛋白（CBPs，以前称为β-角蛋白）组成，最近对两种壁虎物种和一种变色龙的全基因组组装揭示了这些谱系中每一种都有刚毛特异性 CBP 的重复。虽然变色龙只进化出了一次粘性的趾垫，但关于壁虎的数字粘附起源有两种相互竞争的假说，涉及单一起源或多个起源。利用来自三个已发表的壁虎基因组的数据，我研究了壁虎中 CBP 基因的进化，并找到了支持 CBP 基因重复与数字粘附的重复进化有关的假说的证据。尽管这些结果是初步的，但我讨论了如何结合角蛋白和相关蛋白基因的系统发育以及基因重复模型的额外壁虎基因组组装，为与壁虎 CBP 进化相关的几个假说提供严格的测试。这包括一个针对壁虎基因组测序和组装的分类群采样策略，这可能有助于解决围绕数字粘附起源的竞争假说。
