Lectin-binding carbohydrates in sexual differentiation of rat male and female gonads.

Development and sexual differentiation of the mammalian gonad involve changes in the type and distribution of different proteins and glycoproteins in and around the epithelial gonadal cords, the future seminiferous tubules in the testis, and follicles in the ovary. To study changes in cellular carbohydrate-containing compounds in the sex-specific morphogenesis of rat gonads, sections from embryonic, fetal and early postnatal gonads were labelled with seven different fluorescein isothiocyanate (FITC)-conjugated plant lectins of various carbohydrate-binding specificities. Double labelling of laminin with tetramethylrhodamine isothiocyanate (TRITC)-conjugated antibodies was used to outline the epithelial tissues. From the results we conclude that the abundance and similar distribution of carbohydrates in the early gonads of both sexes supports their sexually indifferent nature. Furthermore, the basement membranes of the differentiating gonadal cords in both sexes have common features, which differ, however, from those of the other developing urogenital organs. Changes in carbohydrate composition appear with the sexual differentiation of the gonads; the similarity of the changes in lectin binding to the gonadal cords of embryonic and fetal male, and to postnatal female, suggests similar mechanisms of cell-cell interactions in both sexes although activated at different developmental stages. These carbohydrate specificities at the tissue level should be taken into account together with cell-type specific changes, e.g. in the formation of the zona pellucida, when the phenomenon of polymorphic expression of different compounds is integrated into theories of epithelial differentiation.     

Intermediate filaments and epithelial differentiation of male rat embryonic gonad

The presence and distribution of desmin, vimentin, cytokeratin, and laminin in the gonads of developing male rat embryos (11-17 days) were studied by immunocytochemistry. The findings were correlated with morphological changes of the cells and with the formation of basement membranes, as determined by electron microscopy. The surface epithelial and subepithelial cells of the meesonephros in the prospective gonadal region contained desmin. At the onset of gonadal development, vimentin appeared in the somatic cells of the thickening surface epithelium, which formed the gonadal ridge. Desmin disappeared and cytokeratins appeared in the Sertoli precursor cells at the inception of their epithelial differentiation. Simultaneously, the prospective Sertoli cells became polarized during their assembly into epithelial cell aggregates; the aggregates then fused and formed elongated testicular cords. The epithelial cell differentiation was accompanied by a deposition of basement membrane material around the cords and by an increase of desmin in the cells immediately around the cords. With further differentiation of the testicular cords, some cytokeratins from the Sertoli cells, but not from the cells of the rete cords, disappeared. On the other hand, other cytokeratin polypeptides and vimentin remained in the fetal Sertoli cells. The surface cell layer slowly differentiated towards a proper epithelium after the basic formation of the testicular cords and interstitium. Desmin and vimentin persisted in the interstitial cells throughout the entire study period. The early differentiation of the gonad is apparently under a general sex-independent initiation program. The developmental changes in intermediate filaments offer an opportunity for the further analysis of their general role in early organogenesis. In light of the genetic theory of testicular differentiation, the functions of the regulatory factor(s) include specific organization of cord cells, histological organization into looping cords rather than separated follicles, and male development of the interstitium, surface epithelium and tunica albuginea.