Fibronectin distribution during the development of fetal rat skin.

Fibronectin distribution during fetal rat skin development has been studied immunocytochemically at the light and electron microscope level from 16 days of gestation to birth. The dermal-epidermal junction, the dermis, and connective tissue around developing muscle were shown by light microscopy to be heavily stained throughout this period. The development of hair follicles from about 18 days onward was not associated with any consistent change in fibronectin distribution. The heavy staining of the upper dermis was associated with a high density of mesenchymal cells, and immunoelectron microscopy revealed fibronectin on the surface of many of these cells and in association with the surrounding fine collagen fibrils. At the dermal-epidermal junction, both follicular and interfollicular, fibronectin was localized mainly in the plasma membrane and lamina lucida regions of the basement membrane, and there was also staining associated with the underlying fine collagen fibrils. These observations are further evidence for the proposed role of fibronectin as a mediator of the cell-matrix interactions which are of importance for tissue development and maintenance.