Keratin, type I cytoskeletal 42 (KRT42)

KRT42 and KRT124 exist only as pseudogenes in humans. Similar to the α-keratin genes, KRT42 and KRT75, the β-keratin subfamilies, keratinocyte and claw β-keratins, have duplicated in a non-tandem pattern and form multiple phylogenetically significant clades. Researcher discovery of the KRT42 and KRT75 expansion in the avian lineage.It is likely that these duplicated genes contributed to the evolution of feathers as did the feather β-keratins. Murine Krt42 (formerly K17n) expression has been localized to the nail matrix and nail bed and functional canine KRT42 and KRT124 genes have been identified, suggesting that the nail bed expression of K42 and K124/K90 may be conserved across mammalian and marsupial species, but was lost from the thinner and non-weight-bearing nail units of primates, where both keratins exist only as pseudogenes. Equine KRT42 and KRT124 have a more restricted tissue localization than murine Krt42. Murine Krt42 is expressed in the nail matrix, but the equine lamellar-restricted keratins are not expressed in the homologous coronary region of the hoof wall, as assessed by RT-PCR for KRT42 and multiple methods for KRT124/K124.