Is there a mesonephric cell contribution to the gonadal primordium before sexual differentiation in humans?: An ultrastructural study

Differentiation of the intermediate mesoderm involves a complex series of e vents that result in the formation of the rudiment of the entire adult rena l system, gonads and gonoducts. This work, using light, transmission, and s canning electron microscopy describes in human embryos of different ages, t he development and spatiotemporal organization of the mesonephric nephron, and the development of the gonadal primordium, with the purpose of knowing if and how these two blastemas contribute to the origin of the non germinal cell content of the gonad primordium. Our results show that between Carneg ie stage 13 and 20, the mesonephric nephrons facing the gonadal area, are s eparated by a band of mesenchymal tissue from the gonad primordium and they retain their structural integrities at the level of epithelial wall and th eir basement membrane. The morphological stability of basement membranes of different nephric structures, as well as the mesonephric duct during the p eriod studied, confirm the previous opinion that the mesonephros is functio nal. During the same period of time, the structural events underlying gonad development show that primordial germ cells (PGCs) first invade the gonada l area, and thereafter interact both with epithelial coelomic cells and mes enchymal cells. Both types of cells surround PGCs, initiating the growth an d differentiation of the gonadal primordium. Therefore, a mesonephric cell contribution to the genesis of the somatic cell components of the gonadal p rimordium should be discarded in humans. The present work emphasizes the ne ed for more research in this field.