GERM-CELL CONTROL OF TESTIN PRODUCTION IS INVERSE TO THAT OF OTHER SERTOLI-CELL PRODUCTS

Recent studies have shown that germ cells can regulate testins, two newly identified Sertoli cell proteins that are associated with junctional complexes. To investigate this possibility, several parameters of Sertoli cell function were investigated over 2-120 days post exposure of the rat testes to x-rays (3 Grays). The irradiation-induced loss of spermatogonia resulted in a maturation-depletion process progressively affecting all germ cell classes. Testis weight began to decrease when the most numerous germ cell type (spermatids) began to decline. A complete or near complete recovery of spermatogenesis and of the testis weight had occurred by day 120 post irradiation. There was no significant change in FSH, epididymal androgen-binding protein, and tubule fluid levels during the first weeks after irradiation, when the seminiferious epithelium was depleted of spermatogonia and germ cells up to early spermatids. In contrast, when the number of the more mature forms of spermatids declined (between day 21 and 54), FSH rose and androgen-binding protein as well as fluid production declined. The subsequent recovery of these parameters was also highly correlated with the number of late spermatids. By contrast, testicular testin contents reacted to the depletion of germ cells with a biphasic increase; a doubling occurred when spermatogonia, spermatocytes, and early spermatids were absent (days 4-28), and a 7-fold rise occurred by day 37 when the number of late spermatids had decreased by 50%. By day 54, when the sperm counts had reached a nadir, testin contents had returned to levels corresponding to about four times the control levels; they progressively recovered thereafter. These observations support the postulate that germ cells negatively regulate testins. This possibility was investigated with in vitro experiments showing that addition of germ cell-conditioned medium to Sertoli cell monolayers inhibited testin secretion in a dose-dependent manner. In conclusion this study: 1) highlights the complex interplay between the various germ cell classes in the control of the Sertoli cell function in the adult testis; 2) establishes that germ cell effects may be opposite on different Sertoli cell products; 3) demonstrates that several classes of germ cells negatively control testicular testin contents; and 4) emphasizes the particular role of late spermatids in Sertoli cell regulation.