Genetic studies of MIS signalling in sexual development.

The Müllerian ducts are composed of an epithelium and surrounding mesenchyme that have the potential to differentiate into female reproductive organs, including the oviducts, uterus and upper vagina. In eutherian mammals, Müllerian inhibiting substance/anti-Müllerian hormone (MIS/AMH) secreted by the fetal testis causes the regression of the Müllerian ducts to prevent the differentiation of female reproductive organs in males. MIS signalling in the Müllerian duct is mediated by the MIS type II receptor (MISRII) that is expressed in the mesenchyme surrounding the epithelium. MIS signalling alters the Müllerian duct mesenchyme, leading to the elimination of the ductal epithelium. Loss of MIS signalling, by mutation of MIS or MISRII, leads to the differentiation of female reproductive organs in males that can cause cryptorchidism and infertility. We have exploited the mouse MisrII locus to express heterologous genes in the cellular target of MIS signalling, the Müllerian duct mesenchyme. This approach can be used with conditional genetic strategies to identify factors that are required for the regression of the female genital duct system.