In Vivo Formation Steps of the Hard Alpha-Keratin Intermediate Filament Along a Hair Follicle: Evidence for Structural Polymorphism

The study investigated the formation of hard α-keratin intermediate filaments along a hair follicle using X-ray microdiffraction. It identified four structural zones that corresponded to previously described histological and chemical zones: the bulb zone, elongation zone, keratinization zone, and post-hardening zone. The research revealed two major types of filaments, with one type in the upper zone matching the known architecture of hard α-keratin and another in a lower zone with a larger diameter and low-density core. These findings led to a proposed four-step model for the formation of hard α-keratin filaments, enhancing the understanding of the self-assembly process of keratin in hair follicles.