Limb bud mesenchyme permits seminiferous cord formation in the mouse fetal testis but subsequent testosterone output is markedly affected by the sex of the donor stromal tissue.

Mesonephric stromal cells have previously been shown to migrate into the genital ridge and to be necessary for seminiferous cord formation in organ culture. Here, we asked whether there is a specific requirement for mesonephric stromal cells or whether another source of mesonephric stromal cells can be substituted. Hindlimb buds were immersed in a vital stain and then grafted to male gonad primordia and cultured for 96 hr. Immunocytochemical staining of laminin was used to identify seminiferous cord formation. For Sertoli and Leydig cell differentiation, müllerian inhibiting substance and delta 5-3 beta-hydroxysteroid dehydrogenase were used, respectively. Testosterone secreted into the culture medium was assessed by radioimmunoanalysis. It was found that hindlimb stromal cells, like mesonephric stromal cells, migrate into the genital ridge and allow seminiferous cord formation. These results indicate that mesonephric stromal cells are not specifically required for seminiferous cord formation in the mouse fetal gonad. Furthermore, although Sertoli and Leydig cells differentiate in the gonads grafted to hindlimbs from either male or female embryos, testosterone production was considerably higher with hindlimbs from males. A similar stromal sex effect on subsequent testosterone output was also seen with mesonephric stromal cells.