Migration of mesonephric cells into the mammalian gonad depends on Sry

In mammals, the primary step in male sex determination is the initiation of testis development which depends on the expression of the Y-linked testis determining gene, Sry. The mechanisms by which Sry controls this process ar e unknown. Studies showed that cell migration from the adjacent mesonephros only occurs into XY gonads; however, it was not known whether this effect depended on Sry another Y-linked gene, or the presence of one versus two X chromosomes. Here we provide genetic proof that Sry is the only Y-linked ge ne necessary for cell migration into the gonad. Cell migration from the mes onephros into the differentiating gonad is consistently associated with Sry 's presence and with testis cord formation, suggesting that cell migration plays a critical role in the initiation of testis cord development. The ind uction of cell migration represents the earliest signaling pathway yet assi gned to Sry. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.