Keratin Expression Provides Novel Insight into the Morphogenesis and Function of the Companion Layer in Hair Follicles

The study investigated the expression of keratins K6a and K75 in the companion layer (Cl) of mouse hair follicles during postnatal hair cycling, revealing distinct regulatory patterns. K6a expression began at anagen IIIb and spread from the bulge to the hair bulb, while K75 expression paralleled inner root sheath markers, starting at anagen IIIa. These patterns suggested that the Cl is an integral part of the inner root sheath compartment. The research utilized in situ hybridization, transgenic mouse models, and electron microscopy to map keratin expression, providing insights into hair follicle morphogenesis and function. The study also indicated that mutations in keratin genes could lead to hair and nail disorders, highlighting the structural roles of keratins in maintaining epithelial integrity.