Formation of Surface Membranes in Developing Mammalian Hair Fibers

The study examined the formation of surface membranes in developing mammalian hair fibers, specifically using Merino sheep skin biopsies. It was found that the formation of the fiber cuticle (FC) surface is similar to processes in the epidermal stratum corneum. Initially, FC cells have a plasma membrane adjacent to the inner root sheath (IRS) cuticle, separated by an intercellular space. As the hair matures, exocuticular lamellae form, the FC surface membrane degrades, and intercellular laminae with a stained central band appear. This leads to the cleavage between IRS cuticle and FC, releasing the hair into the pilary canal. The mature hair surface consists of keratinized cells with a developed exocuticle and a-layer, coated with paired laminae derived from intercellular laminae, challenging previous beliefs that the cuticle surface membrane is a modified plasma membrane.