Sex-specific localization of laminin α5 chain in the differentiating rat testis and ovary

Abstract

The localization of laminin (Ln) α5, β1 and β2 chains in the differentiating 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 α5 and β1 chains, but not of Ln β2 chain. The sexual differentiation of the embryonic male gonadal cords included rapid sex-specific disappearance of the incipient Ln α5 chain. The rete testis cords, in contrast, remained positive for Ln α5 chain. In the postnatal testis, the Ln α5 chain reappeared in Ln β1 chain-positive cord basement membranes, which also became positive for Ln β2 chain. The differentiating myoid cells also gradually became positive for both Ln α5 and Ln β1 chains. In the ovary Ln α5 chain persisted in BMs of the cords throughout the fetal phase. Small and newly formed follicles in the early postnatal rat overy were also positive for Ln α5 chain, whereas growing and large follicles were negative. During the early postnatal phase, Ln β1-chain positive follicular BMs became also positive for the Ln β2 chain. Basement membranes of testicular and ovarian surface epithelia contained the Ln α5 chain throughout the study. The blood vessels of the male and female gonad showed differentiation-dependent variation in their reactivity for the Ln α5 and β2 chains. The present results show that the Ln α5 chain is an early molecular marker for sexual differentiation, which therefore may be regulated by the testis-determining factors. The results also show that in the early postnatal rat ovary, the follicular basement membranes are heterogeneous in their Ln content, which may offer a means to distinguish different follicular populations from each other and to identify the different stages of follicular growth.