Immunohistochemical Localization of Laminin and Cytokeratin in Embryonic Alligator Gonads

Gonadal sex differentiation is temperature‐dependent in Alligator mississippiensis; testis differentiation occurs in embryos incubated at 33°C and ovary differentiation occurs in embryos incubated at 30°C. Laminin and cytokeratin were examined immunohistochemically in the gonads of alligator embryos incubated at these temperatures. The aim of this study was to determine whether these structural proteins show the same sex‐specific expression patterns reported for mammalian embryos, and to assess their usefulness as early markers of gonadal differentiation in species with temperature‐dependent sex determination. Laminin delineated enlarged seminiferous cords in differentiating testes from developmental stage 23 to hatching. Laminin distribution was more diffuse and revealed smaller cords of cells in differentiating ovaries. Cytokeratin was also detected in developing gonads of both sexes. Cytokeratin became concentrated in the basal cytoplasm of differentiating Sertoli cells in developing testes. In developing ovaries, prefollicular cells of the ovarian cortex and cell cords in the medulla stained strongly for cytokeratin. Cytokeratin did not show the same basal distribution in female medullary cord cells as seen in the Sertoli cells of testes, however. These sex‐specific patterns of laminin and cytokeratin distribution in embryonic alligator gonads may serve as early markers of sexual differentiation. 1995 The Royal Swedish Academy of Sciences