Alibardi Lorenzo
Department of Experimental and Evolutionary Biology, University of Bologna, 40126 Bologna, Italy.
Int Rev Cytol. 2006;253:177-259. doi: 10.1016/S0074-7696(06)53005-0.
This review presents comparative aspects of epidermal keratinization in vertebrates, with emphasis on the evolution of the stratum corneum in land vertebrates. The epidermis of fish does not contain proteins connected with interkeratin matrix and corneous cell envelope formation. Mucus-like material glues loose keratin filaments. In amphibians a cell corneous envelope forms but matrix proteins, aside from mucus/glycoproteins, are scarce or absent. In reptiles, birds, and mammals specific proteins associated with keratin become relevant for the production of a resistant corneous layer. In reptiles some matrix, histidine-rich and sulfur-rich corneous cell envelope proteins are produced in the soft epidermis. In avian soft epidermis low levels of matrix and cornified proteins are present while lipids become abundant. In mammalian keratinocytes, interkeratin proteins, cornified cell envelope proteins, and transglutaminase are present. Topographically localized areas of dermal-epidermal interactions in amniote skin determine the formation of skin derivatives such as scales, feathers, and hairs. New types of keratin and associated proteins are produced in these derivatives. In reptiles and birds beta-keratins form the hard corneous material of scales, claws, beaks, and feathers. In mammals, small sulfur-rich and glycine-tyrosine-rich proteins form the corneous material of hairs, horns, hooves, and claws. Molecular studies on reptilian beta-keratins show they are glycine-rich proteins. They have C- and N-terminal amino acid regions homologous to those of mammalian proteins and a central core with homology to avian scale/feather keratins. These findings suggest that ancient reptiles already possessed some common genes that later diversified to produce some keratin-associated protein in extant reptiles and birds, and others in mammals. The evolution of these small proteins represents the more recent variation of the process of cornification in vertebrates.
本综述介绍了脊椎动物表皮角质化的比较情况，重点关注陆地脊椎动物角质层的进化。鱼类的表皮不含与角蛋白中间基质和角质细胞包膜形成相关的蛋白质。黏液样物质黏合松散的角蛋白丝。在两栖动物中，形成了细胞角质包膜，但除黏液/糖蛋白外，基质蛋白稀缺或不存在。在爬行动物、鸟类和哺乳动物中，与角蛋白相关的特定蛋白质对于产生抗性角质层至关重要。在爬行动物中，一些基质、富含组氨酸和富含硫的角质细胞包膜蛋白在柔软的表皮中产生。在鸟类的柔软表皮中，基质和角质化蛋白含量较低，而脂质含量丰富。在哺乳动物的角质形成细胞中，存在角蛋白中间蛋白、角质化细胞包膜蛋白和转谷氨酰胺酶。羊膜动物皮肤中真皮与表皮相互作用的地形定位区域决定了皮肤衍生物如鳞片、羽毛和毛发的形成。在这些衍生物中产生了新型的角蛋白和相关蛋白质。在爬行动物和鸟类中，β-角蛋白形成鳞片、爪子、喙和羽毛的坚硬角质物质。在哺乳动物中，富含硫和富含甘氨酸-酪氨酸的小蛋白质形成毛发、角、蹄和爪子的角质物质。对爬行动物β-角蛋白的分子研究表明它们是富含甘氨酸的蛋白质。它们具有与哺乳动物蛋白质同源的C端和N端氨基酸区域，以及与鸟类鳞片/羽毛角蛋白同源的中央核心。这些发现表明，古代爬行动物已经拥有一些共同的基因，这些基因后来发生了分化，在现存的爬行动物和鸟类中产生一些与角蛋白相关的蛋白质，在哺乳动物中则产生其他相关蛋白质。这些小蛋白质的进化代表了脊椎动物角质化过程中较新的变异。
