Extracellular matrix molecules and follicle morphogenesis in ovine skin

Chondroitin sulphate, fibronectin, laminin and the hyaluronan receptor, CD44, were localized in ovine skin during follicle morphogenesis. Prior to initiation, chondroitin sulphate was detected in the mesenchyme adjacent to the dermal-epidermal junction and showed an approximately regular periodicity in staining intensity. With the appearance of follicle primordia, the more strongly stained regions of the matrix were associated with mesenchymal condensations. During later development and in the mature follicle, staining was localized to the matrices of cells of the dermal sheath and papilla. CD44 was also localized in the mesenchymal condensations at follicle initiation and, subsequently, in the dermal sheath. Fibronectin staining was confined to the mesenchyme prior to follicle formation and became associated with presumptive papilla and dermal sheath cells during follicle formation and maturation. Fibronectin antisera detected an approximately 220 kDa protein in western blots of adult and fetal skin. An additional band of 150 kDa was also observed prior to follicle initiation. In contrast, laminin was predominantly restricted to the basal laminae of developing and mature follicles. The aggregative behaviour of ovine papilla cells was examined in vitro. The number and size of aggregates were not affected by inclusion of chondroitin sulphate or fibronectin in the culture medium, but both increased in the presence of hyaluronidase. Chondroitinase had the opposite effect and beta-D-xyloside completely abolished aggregative behaviour. In conclusion, the appearance of certain matrix molecules may presage morphogenetic movements of cells at follicle initiation and regulate patterns of follicle distribution in skin during fetal life.