The Molecular Mechanism Of Hair Degradation In Marine Mammals

Diversity of hair in marine mammals was suggested as an evolutionary innovation to adapt aquatic environment,yet its genetic basis remained poorly explored.We scanned a-keratins and KRTAP genes,major structural components of hair,in 15 genomes of mammalian species,including seven cetaceans,two pinnipeds,manatee and five terrestrial species.The result showed that the average number of a-keratin and KRTAP genes in cetaceansa was significantly lower than that of artiodactyl species(a-keratin 37.29 vs.58.67,KRTAP 51.7 vs.119.4)whereas the average percentage of pseudogenes of a-keratin and KRTAP in cetaceans was significantly higher than that in artiodactylans(a-keratins 29.89%vs.8.52%,KRTAPs 68.5%vs.32.7%),which may be associated with cetacean hairless phenotype.Increased gene loss and pseudogenization rate was especially identified in hair follicle-specific keratin genes in cetaceans(average pseudogenization rate in cetaceans vs.artiodactylans:44.33%vs.3.80%).Additionally,much more number of a-keratins and KRTAPs genes and relatively lower pseudogenization rate was examined in the baleen whale than toothed whale,possibly due to the specific keratinized baleen in the former.,However,comparative evolution pattern of a-keratin and KRTAP gene repertoire in the pinnipeds and their terrestrial relatives is likely due to abundant hair in pinnipeds to keep warm when they went ashore to mate,give birth,molt or escape from predators.In contrast,the fully aquatic manatee is greatly reduced body hair but with perioral bristles and bristle-like hairs on the oral disk that have specialized sensory and feeding function.Accordingly,the manatee still remained the comparable a-keratins number and rate of pseudogenization to its terrestrial relative.However,when another components of hair,KRTAP,are considered,a significant gene number reduction(81 in manatee vs 112 in elephant)and increased pseudogenization rate(41.98%in manatee vs 20%in elephant)were detected in manatee.Finally,it was interesting to find that a reduced number of functional KRTAP genes,high percentage of KRTAP pseudogenes,and common loss of a-keratin genes(K39?K9?K42?K74)and KRTAP genes(KRTAP9)in both cetaceans and manatees,likely as a result of convergent hair-loss phenotype to inhabit completely aquatic environment in both groups.In this study,we provide a comprehensive characterization of a-keratin and KRTAP genes among marine mammals and shed light on the mechanisms involved in the evolution of the two-gene family.Meanwhile,our study first indicated the genetic basis of hair diversities of marine mammals and provided new evidence for the origin and evolution of hair.