Emx2 developmental expression in the primordia of the reproductive and excretory systems

The development of the urogenital system hasalways attracted many investigators owing to the peculiaraspects of the embryology of the reproductive and excretoryorgans and to the high number of congenital anomaliesrelated to these structures. It is remarkable becauseof the common origin of the kidneys, gonads, and genitaltracts from the intermediate mesoderm and because differentiation of these organs involves extensive mesenchymeto epithelium transition. Our knowledge about themolecular mechanisms controlling the differentiation ofthese diverse structures from the same precursor has takenadvantage of gene expression data and gene-targetingexperiments using genes with a specific expression patternin the urogenital system. A more detailed functionin kidney development has been postulated for transcriptionfactors such as WT-1, Pax-2 or other molecules suchas glial cell line-derived neurotrophic factor (GDNF),Wnt-4, c-ret. In the present work we have described theexpression pattern of the homeobox-containing geneEmx2 during the development of the urogenital system inmouse embryos. We have found that Emx2 is expressedin the early primordia of the organs that will form the excretoryand reproductive systems. In particular we havefound that Emx2 is expressed in the epithelial componentsof pronephros and mesonephros, in Wolffian andMüllerian ducts, in the ureteric buds with their branchesand in the early epithelial structures derived from metanephrogenic mesenchyme. Emx2 is also intensely expressedin the “bipotential” or “indifferent” gonads andovaries. These data and the recent finding that Emx2 homozygousmutant mice die soon after birth because ofthe absence of kidneys indicate an essential role of Emx2in the morphogenesis of the urogenital system.