Expression of laminin, type IV collagen and fibronectin molecules is related to embryonal skin and epidermal appendage morphogenesis.

Basement membrane zones are specialized sheets--like arrangements of extracellular matrix proteins and glycosaminoglycans, and act as an interface between parenchymal cells and support tissue. They separate epithelium, endothelium, muscle cells and Schwann cells from adjacent connective tissue stroma, and also from a limiting membrane in the central nervous system. They are involved in several cellular and biological processes, including adhesion, migration and cellular differentiation. Basement membranes have five major components: collagen type IV, laminin, heparan sulfate, entactin, and fibronectin. In addition, there are numerous minor and poorly characterized protein and glycosaminoglycan components. The various components of the basement membranes of the skin (collagen type IV, proteoglycans--heparan sulfate, laminin, entactin and fibronectin) are products of the epithelial (epidermal) cells. We studied immunohistochemically the origin, the first appearance and distribution of the adhesive extracellular glycoprotein laminin and the fibrillar proteins of the extracellular matrix collagen type IV and fibronectin in the basement membranes of fetal human skin between 12 to 21 weeks of gestational age. Additionally, we studied the expression of vimentin in the extracellular matrix of the epithelial/mesenchyme junction of the skin. This study demonstrates clearly that the expression of the antigens laminin, collagen type IV and fibronectin starts in the germinative epithelial cells of the skin at the bulbs of the hair follicles (12th week for fibronectin and 19th week for laminin and collagen type IV), and migrating progressively involves the epithelial epidermal cells of the covering skin, as well as, the basement membrane at the dermal-epidermal junction in that region (between 20 to 21 weeks of gestational age).