EMX2 DEVELOPMENTAL EXPRESSION IN THE PRIMORDIA OF THE REPRODUCTIVE AND EXCRETORY SYSTEMS

The development of the urogenital system has always attracted many inv estigators owing to the peculiar aspects of the embryology of the repr oductive and excretory organs and to the high number of congenital ano malies related to these structures. It is remarkable because of the co mmon origin of the kidneys, gonads, and genital tracts from the interm ediate mesoderm and because differentiation of these organs involves e xtensive 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 express ion data and gene-targeting experiments using genes with a specific ex pression 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 neu rotrophic factor (GDNF), Wnt-4, c-ret. In the present work we have des cribed the expression pattern of the homeobox-containing gene Emx2 dur ing the development of the urogenital system in mouse embryos. We have found that Emx2 is expressed in the early primordia of the organs tha t will form the excretory and reproductive systems. In particular we h ave found that Emx2 is expressed in the epithelial components of prone phros and mesonephros, in Wolffian and Mullerian ducts, in the ureteri c buds with their branches and in the early epithelial structures deri ved from metanephrogenic mesenchyme. Emx2 is also intensely expressed in the ''bipotential'' or ''indifferent'' gonads and ovaries. These da ta and the recent finding that Emx2 homozygous mutant mice die soon af ter birth because of the absence of kidneys indicate an essential role of Emx2 in the morphogenesis of the urogenital system.