Hoxc13 and Homologs of Mammalian Hair Keratins Are Required for the Cornification of Nuptial Pads in Xenopus Frogs

The study investigates the role of Hoxc13 and type II hair keratin homolog krt59 in the cornification of nuptial pads in Xenopus frogs. It reveals that the expression of Hoxc13 is enriched in the skin of the forelimbs, and its inactivation via CRISPR-Cas9 leads to the loss of krt59 expression and epithelial cornification in nuptial pads. This suggests that cornified nuptial spines have evolved similarly to mammalian hair by adapting the ancestral cornification program of skin appendages. The findings highlight the evolutionary parallel between the development of these structures in frogs and hair in mammals.