MALE-SPECIFIC CELL-MIGRATION INTO THE DEVELOPING GONAD

Background: The gene Sry acts as a developmental switch, initiating a pathway of gene activity that leads to the differentiation of testis r ather than ovary from the indifferent gonad (genital ridge) in mammali an embryos, The early events following Sry expression include rapid ch anges in the topographical organization of cells in the XY gonad. To i nvestigate the contribution of mesonephric cells to this process, gona ds from wild-type mice (CD1), and mesonephroi from a transgenic strain ubiquitously expressing beta-galactosidase (ROSA26), were grafted tog ether in vitro, After culture, organs were fixed and stained for beta- galactosidase activity to identify cells contributed from the mesoneph ros to the male or female gonad, Results: Migration of mesonephric cel ls occurred into XY but not XX gonads from 11.5-16.5 days post coitum (dpc), Somatic cells contributed from the mesonephros were distinguish ed by their histological location and by available cell-specific marke rs, Some of the migrating cells were endothelial; a second population occupied positions circumscribing areas of condensing Sertoli cells; a nd a third population lay in close apposition to endothelial cells. Co nclusions: Migration from the mesonephros to the gonad is male specifi c at this stage of development and depends on an active signal that re quires the presence of a Y chromosome in the gonad. The signals that t rigger migration operate over considerable distances and behave as che moattractants. We suggest that migration of cells into the bipotential gonad may have a critical role in initiating the divergence of develo pment toward the testis pathway.