BASIC FIBROBLAST GROWTH-FACTOR IS A TESTICULAR GERM-CELL PRODUCT WHICH MAY REGULATE SERTOLI-CELL FUNCTION

Previously, a proteinacious factor secreted by a mixture of rat testic ular spermatocytes and round spermatids was shown to stimulate transfe rrin mRNA and protein levels in Sertoli cells. To identify the germ ce ll-secreted proteins which affect Sertoli cell functions, concentrated germ cell-conditioned medium was fractionated by reverse-phase HPLC. The fraction which eluted at 35% acetonitrile increased transferrin se cretion in Sertoli cell cultures 2.4-fold above the basal level. Both the active fraction and a protein extract from cultured germ cells wer e positive for basic fibroblast growth factor (bFGF) as determined by Western blot analysis and immunoprecipitation. The apparent molecular sizes of the immunoreactive proteins were 30, 27, and 24 kilodaltons ( kDa). By immunohistochemistry, bFGF was shown to be present in pachyte ne spermatocytes and Leydig cells. The bFGF receptor was also examined by immunohistochemistry and found to be present in Leydig cells, roun d and elongated spermatids, and Sertoli cells. The presence of recepto rs was more pronounced in stages I-VIII. Western blot analysis confirm ed that the receptors were expressed in isolated round spermatids, elo ngated spermatids, and Sertoli cells. Two major receptor species with apparent molecular sizes of 120 and 145 kDa were detected in the rat t estis. Germ cells contained both of these receptors, but Sertoli cells possessed only the 120-kDa receptor. From these experiments, it is ev ident that bFGF is a germ cell product which may regulate Sertoli cell function. The expression of bFGF and its receptor may be an important component of germ cell-Sertoli cell and/or germ cell-germ cell commun ication during spermatogenesis.