Spermatogenesis is a continuous process which starts during the embryo-fetal development. Auto, para and juxtacrine relations indicate the interdependence of the interstitial cells (Leydig) with the peritubular cells (lamina propria) and sustentacular cells (Sertoli). Certain morphogens are fundamental in this process. Sustentacular cells are able to regulate differentiation and function and peritubular interstitial cells through production of IGF1, TGFA, TGFB and DHH. Peritubular cells are able to produce P-Mod-S regulating differentiation sustentacular cells and through FGF2 and FGF9 modulate epithelial-mesenchymal transitions between sustentacular cells and mesonephros. They also remodel the basal membrane of the testicular condom and regulate the differentiation and function of the interstitial cells by means of IGF1, TGFA and TGFB. Interstitial cells are responsible for the production of testosterone and INSL3, influencing male sexual differentiation. It is suggested that they come from mesenchymal cells of the coelomic epithelium and mesonephros. However, other authors propose their origin from cells of the neural crest. These influence through paracrine mechanisms proliferation sutentaculares cells by activin A, resulting in the expansion of cord testicular. The interactions between the different cell populations through morphogens induce a fundamental epithelial-mesenchymal transition in the formation and differentiation of the male gonad.

KEY WORDS: Fetal testicle; Morphogen; Sustentacular cell; Peritubular cell; Interstitial cell.