Sex-specific localization of laminin alpha 5 chain in the differentiating rat testis and ovary

The localization of laminin (Ln) alpha 5, beta 1 and beta 2 chains in the d ifferentiating rat testis and ovary was studied by immunolabeling light and electron microscopy. The initial formation of the male and female gonadal blastemas included an emergence of Ln alpha 5 and beta 1 chains, but not of Ln beta 2 chain. The sexual differentiation of the embryonic male gonadal cords included rapid sex-specific disappearance of the incipient Ln alpha 5 chain. The rete testis cords, in contrast, remained positive for Ln alpha 5 chain. In the postnatal testis, the Ln alpha 5 chain reappeared in Ln bet a 1 chain-positive cord basement membranes, which also became positive for Ln beta 2 chain. The differentiating myoid cells also gradually became posi tive for both Ln alpha 5 and Ln beta 1 chains. In the ovary Ln alpha 5 chai n persisted in BMs of the cords throughout the fetal phase. Small and newly formed follicles in the early postnatal rat every were also positive for L n alpha 5 chain, whereas growing and large follicles were negative. During the early postnatal phase, Ln beta 1-chain positive follicular BMs became a lso positive for the Ln beta 2 chain. Basement membranes of testicular and ovarian surface epithelia contained the Ln a5 chain throughout the study. T he blood vessels of the male and female gonad showed differentiation-depend ent variation in their reactivity for the Ln alpha 5 and beta 2 chains. The present results show that the Ln alpha 5 chain is an early molecular marke r for sexual differentiation, which therefore may be regulated by the testi s-determining factors. The results also show that in the early postnatal ra t ovary, the follicular basement membranes are heterogeneous in their Ln co ntent, which may offer a means to distinguish different follicular populati ons from each other and to identify the different stages of follicular grow th.