Structural proteins in sexual differentiation of embryonic gonads.

Sexual differentiation of embryonic gonads was studied by immunocytochemical analysis of cytoskeleton, basement membrane and extracellular matrix. The epithelial cells of the prospective gonadal region in both sexes contained vimentin and desmin intermediate filament proteins but not cytokeratin. Basement membrane components laminin, collagen types IV and V, heparan sulfate proteoglycan, and fibronectin were seen in an unorganized form in the extracellular space. The development of the gonads started by proliferation of the pregonadal epithelial cells, which formed separate clusters and loose mesenchyme. In the male gonad the clusters joined together into elongated cords, outlined by basement membrane components. The cord cells became polarized epithelial cells, and cytokeratin appeared with the disappearance of desmin in their cytoplasm. Desmin and vimentin remained in the interstitial cells. In the female gonad the clusters were smaller, and the cords were irregular in shape and size. Desmin disappeared from the cord cells and cytokeratin appeared, but more slowly and less well polarized than in the testis. The present results show that after common early development, the sexual differences in gonads emerge as different organization of the internal epithelial tissue with different timing of changes in intra- and extracellular components.