DIFFERENTIAL DISTRIBUTION OF THE ALPHA(6) SUBUNIT OF INTEGRINS IN THEDEVELOPMENT AND SEXUAL-DIFFERENTIATION OF THE MOUSE TESTIS

The distribution of the alpha(6) subunit of integrins in the developme nt and sexual differentiation of mouse testis was analyzed by light an d electron microscopy during the embryonic, fetal and early postnatal periods. At the pregonadal phase only the epithelial cells of the meso nephric duct and of the distal mesonephric tubules showed a reaction t o alpha(6), whereas the surface epithelium and the mesenchyme of the m esonephros were negative or contained only a rudimentary amount of the alpha(6) subunit. With the formation of the gonadal ridge and the tes ticular blastema, the gonadal cells became positive for the alpha(6) s ubunit. This expression remained in embryonic cord cells and in the va scular endothelial cells, whereas the differentiating cells of the sur face epithelium, tunica albuginea, the Leydig cells, and the interstit ial mesenchymal cells were negative. With the fetal and postnatal diff erentiation, the expression of the alpha(6) subunit gradually diminish ed in the cord cells, and by the prepubertal phase, alpha(6) was found only at adhesion sites between some Sertoli cells. Similar changes we re seen in the mesonephric duct and tubules, and in the rete cords. Th e presence of alpha(6) in regions undergoing developmental cell aggreg ation processes and their disappearance during tissue maturation, sugg est that alpha(6) plays a specific but transient role in gonadal cell adhesion necessary for the histogenetic organization of the testis. In addition to its role in developing and organizing cells, alpha(6) int egrin was also a prominent component in degenerating cells. The variab le expression of the alpha(6) subunit of integrins observed in the epi thelial cells of the internal genitalia implies that integrins and pro bably other adhesion molecules are key elements in gonadal sex differe ntiation.