Effects of extracellular matrix on differentiation of mouse fetal gonads in the absence of mesonephros in vitro.

The influence of mesonephric tissues and the extracellular matrix on mouse gonadal differentiation was examined in vitro. Gonadal ridges, with or without the adjacent mesonephric region, were removed from mouse embryos on day 12 post coitum (p.c.), and cultured in the presence or absence of reconstituted basement membrane (matrigel) for 5 days. Culturing control undifferentiated testes with mesonephric tissues induced normal testicular differentiation. When testes without mesonephric tissues were cultured in the absence of matrigel, testicular cord formation was not observed in the explants. Sertoli cells were irregularly arranged in the testicular parenchyma, and no continuous basal lamina was formed around the Sertoli cells. However, when testes without mesonephric tissues were embedded in matrigel and cultured for 5 days, the Sertoli cells were organized into testicular cord-like structures. The Sertoli cells positioned at the base of the cord-like structures were closely connected to the matrigel at their basal surface, and showed a polarized distribution of vimentin filaments in their basal cytoplasm. Leydig cells, on the other hand, were differentiated in all testicular explants. In all ovarian explants, germ cells normally entered meiotic prophase. Therefore, these findings indicate that the extracellular matrix permits testicular differentiation in the absence of the mesonephros, and that removal of mesonephric tissues leads to developmental failure of cord formation because the components of the extracellular matrix around pre-Sertoli cells are incomplete.