K6irs1, K6irs2, K6irs3, And K6irs4 Represent The Inner-Root-Sheath-Specific Type II Epithelial Keratins Of The Human Hair Follicle

The study identified and characterized four inner-root-sheath-specific type II epithelial keratins, K6irs1, K6irs2, K6irs3, and K6irs4, in the human hair follicle. K6irs3 and K6irs4 were newly discovered and, along with K6irs1 and K6irs2, formed a distinct gene cluster on chromosome 12q13. These keratins were expressed in specific layers of the inner root sheath (IRS), with K6irs3 starting in the lowermost bulb region and K6irs4 restricted to the Huxley layer. The research provided insights into the structural and evolutionary relationships among IRS keratins and their roles in hair follicle compartments, enhancing the understanding of hair follicle biology and keratinization processes. Additionally, the study highlighted the role of Flügelzellen, specialized Huxley cells marked by K6irs4, in contributing to the flexibility and resilience of the hair follicle structure.