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

The development of the urogenital system has always attracted many investigators owing to the peculiar aspects of the embryology of the reproductive and excretory organs and to the high number of congenital anomalies related to these structures. It is remarkable because of the common origin of the kidneys, gonads, and genital tracts from the intermediate mesoderm and because differentiation of these organs involves extensive mesenchyme to epithelium transition. Our knowledge about the molecular mechanisms controlling the differentiation of these diverse structures from the same precursor has taken advantage of gene expression data and gene-targeting experiments using genes with a specific expression pattern in the urogenital system. A more detailed function in kidney development has been postulated for transcription factors such as WT-1, Pax-2 or other molecules such as glial cell line-derived neurotrophic factor (GDNF), Wnt-4, c-ret. In the present work we have described the expression pattern of the homeobox-containing gene Emx2 during the development of the urogenital system in mouse embryos. We have found that Emx2 is expressed in the early primordia of the organs that will form the excretory and reproductive systems. In particular we have found that Emx2 is expressed in the epithelial components of pronephros and mesonephros, in Wolffian and Müllerian ducts, in the ureteric buds with their branches and in the early epithelial structures derived from metanephrogenic mesenchyme. Emx2 is also intensely expressed in the "bipotential" or "indifferent" gonads and ovaries. These data and the recent finding that Emx2 homozygous mutant mice die soon after birth because of the absence of kidneys indicate an essential role of Emx2 in the morphogenesis of the urogenital system.