[Epithelial cell differentiation in precocious testicular morphogenesis].

Testicular morphogenesis in the rat foetus, requires at least two distinct steps of differentiation. One of these steps is the differentiation of Sertoli cells. This is the first morphological event which allows identification of the male gonad. The other truly morphogenetic step is the acquisition of epithelial characteristics by Sertoli cells: aggregation, polarization, expression of cytokeratin. This step, which is obtained in vitro if gonads are cultured in synthetic medium, is impaired when gonads are cultured in serum-supplemented medium. In both cases Sertoli cells differentiate morphologically and physiologically. Immunohistochemically detectable cytokeratin (monoclonal antibody Lu-5) was found in Sertoli cells incorporated in seminiferous cords either in vivo or in vitro, but not in undifferentiated somatic cells or in Sertoli cells of cordless gonads. These results suggest that the expression of cytokeratin, in the differentiating testis, cannot be considered as a marker of the origin of the cells, but rather is related to the adhesion of Sertoli cells to each other.