Research Division of Biology and Pathobiology of the Skin, Department of Dermatology, Medical University of Vienna, Vienna, Austria.
Adv Exp Med Biol. 2018;1054:33-45. doi: 10.1007/978-981-10-8195-8_4.
The evolution of keratins was closely linked to the evolution of epithelia and epithelial appendages such as hair. The characterization of keratins in model species and recent comparative genomics studies have led to a comprehensive scenario for the evolution of keratins including the following key events. The primordial keratin gene originated as a member of the ancient gene family encoding intermediate filament proteins. Gene duplication and changes in the exon-intron structure led to the origin of type I and type II keratins which evolved further by nucleotide sequence modifications that affected both the amino acid sequences of the encoded proteins and the gene expression patterns. The diversification of keratins facilitated the emergence of new and epithelium type-specific properties of the cytoskeleton. In a common ancestor of reptiles, birds, and mammals, a rise in the number of cysteine residues facilitated extensive disulfide bond-mediated cross-linking of keratins in claws. Subsequently, these cysteine-rich keratins were co-opted for an additional function in epidermal follicular structures that evolved into hair, one of the key events in the evolution of mammals. Further diversification of keratins occurred during the evolution of the complex multi-layered organisation of hair follicles. Thus, together with the evolution of other structural proteins, epithelial patterning mechanisms, and development programmes, the evolution of keratins underlied the evolution of the mammalian integument.
角蛋白的进化与上皮组织及其附属物（如毛发）的进化密切相关。在模式物种中的角蛋白特征和最近的比较基因组学研究，为角蛋白的进化提供了一个全面的情景，包括以下关键事件。原始角蛋白基因起源于编码中间丝蛋白的古老基因家族的成员。基因复制和外显子-内含子结构的变化导致了 I 型和 II 型角蛋白的起源，它们通过影响编码蛋白的氨基酸序列和基因表达模式的核苷酸序列修饰进一步进化。角蛋白的多样化促进了细胞骨架的新特性和上皮类型特异性的出现。在爬行动物、鸟类和哺乳动物的共同祖先中，半胱氨酸残基数量的增加促进了角蛋白在爪中的广泛二硫键介导交联。随后，这些富含半胱氨酸的角蛋白被另一个功能所采用，即表皮毛囊结构的功能，这是哺乳动物进化的关键事件之一。在毛囊的复杂多层组织的进化过程中，角蛋白进一步多样化。因此，角蛋白的进化与其他结构蛋白、上皮模式形成机制和发育程序一起，为哺乳动物的表皮进化奠定了基础。
