Novel Type I Hair Keratins K39 and K40 Are the Last to be Expressed in Differentiation of the Hair: Completion of the Human Hair Keratin Catalog

The study identified two novel type I hair keratins, K39 and K40, which were the last to be expressed during hair follicle differentiation, completing the human hair keratin catalog with 17 members. These keratins were expressed in the upper hair cuticle and cortex, with K39 also in the upper medulla, and showed distinct expression patterns with less than 60% sequence identity to each other and other type I keratins. The research provided insights into the sequential expression and complex interplay of type I and type II keratins in different hair follicle zones during terminal differentiation.