Structural and regulatory macromolecules in sex differentiation of gonads.

The manifestations of sex determination were studied in vivo by detection and localization of structural and regulatory macromolecules (type IV collagen alpha 1, alpha 2, alpha 3, alpha 4, and alpha 5; laminin alpha 5, beta 1, and beta 2; cytokeratins 18 and 19, desmin, vimentin; integrin alpha(6;) anti-Müllerian hormone (AMH); and SOX9 in developing male and female gonads by light and electron microscopy, immunocytochemistry, and protein analysis. The goal has been to find sex-related differences and on this basis to offer new molecules to be tested further for a possible role in sex determination. Specific antibodies for each molecule or for a defined subchain were used to allow tentative correlation with specific genes. Sex-dependent differences in timing and localization were found in laminin alpha 5; collagen, alpha 3, alpha 4, and alpha 5; cytokeratin 19; AMH; and SOX9. On this basis we hypothesize that the transcription factors for the mentioned structural proteins must be directly or indirectly involved in the regulatory chain of gonadal sex differentiation. Especially promising is the finding in the rat that laminin alpha 5 chain disappears from the basement membrane of embryonic testicular cords (Sertoli cells) when AMH secretion by Sertoli cells starts, and that the same chain reappears as the AMH disappears two weeks after birth. Via AMH as an intermediary factor, we now have for the first time a putative cascade of regulatory molecules from SRY, SF1, and SOX9 to a component of a structural protein (laminin alpha 5 chain) which directly participates in the formation of the basement membrane of the testicular cords. J. Exp. Zool. 290:523-528, 2001.