Molecular Evolution Of Type Ⅰ Hair Keratin And IRS Keratin Genes Of Mammalian

In the process of mammalian evolution, the mutation of hair keratin does not produce lethal effects and can be maintained easily. In this study, chromosome pattern of typeⅠh air keratin gene clusters and IRS keratin gene clusters from 10 kinds of mammals are compared. Mammalian typeⅠkeratin genes are located on the same chromosome location, and with basically the same as the order, reflecting the conservative nature of evolution. Mammalian typeⅠhair keratin gene clusters are located between the KRT23 and KRT13/KRT15 gene; The KRT39, KRT40 gene cluster and KRT33, KRT34, KRT31, KRT37, KRT38, KRT32, KRT35, KRT36 gene cluster are separated by a KAP gene cluster.TypeⅠIRS keratin gene clusters are located between the KRT24 and KRT10 gene, even if one or a few genes are missing that will not affect chromosome location and arrangement of other genes. This conservative position information and the evolution of genes have a relationship with the origin of the hair. TypeⅠhair keratin and IRS keratin genes are not unique to mammals, birds and reptiles have the existence of their homologous genes or gene fragments. The number of Rodents functional hair keratin genes significantly less than other mammals. The number of human typeⅠhair keratin and the IRS keratin genes are similar to other primates.TypeⅠmammalian hair keratin genes KRT31～38 are much higher than the GC content of KRT39, 40 gene cluster and IRS keratin genes, indicating that the gene conversion frequency of the former should be more than the latter. The typeⅠhair keratin and IRS keratin genes of the platypus are much higher than the GC content of opossum. The typeⅠhair keratin and IRS keratin genes are conservative in the number of introns.Phylogenetic tree analysis show that the hair keratin genes KRT39, KRT40 and KRT33, KRT34, KRT31, KRT37, KRT38, KRT32, KRT35, KRT36 format two separate units from two ancestor genes respectively; this is in line with the distribution of chromosomes. KRT39, KRT40 KRT32, KRT35, KRT36 genes are differentiation earlier than the mammalian species'and phylogenetic tree is essentially a reflection of the relationship between the evolution of species. The hair keratin KRT33, KRT34, KRT31 genes are the latest differentiational hair keratin genes, they are obviously later than the differentiation of mammalian species,and still very active.The phylogenetic tree of human keratins reflect that typeⅠIRS keratin genes are originated from KRT24 gene, the evolutionary tree of mammalian typeⅠIRS keratin KRT25,KRT26,KRT27,KRT28 format independent branch, indicating that their differentiation is prior to the differentiation of mammalian species. It is found that there are highly homologous to the IRS keratin gene sequences in birds and reptiles, show the ancestral genes of IRS already exist in the reptiles. TypeⅠhair keratin and IRS keratin genes promoter sequences are different, indicating that their expression and regulation are different.The homologous sequence of typeⅠhair keratin and IRS keratin genes exist in reptiles, therefore the ancestors of mammals should have a diverse family of KRT. By comparing the hair keratin and IRS keratin genes on the genome of mammals, reptiles and birds, the differentiation of functionally hair keratin and IRS keratin may be a prerequisite for hair formation. Study on molecular evolution of typeⅠhair keratin and IRS keratin genes provide new evidence for the origin and evolution of hair.