020. HORMONAL REGULATION OF SPERMATOGENESIS

Abstract

Spermatogenesis is a spatially and temporally co-ordinated proliferation of the germinal epithelium in the semeniferous tubules. The germ cells are embedded in a scafolding formed by adjacent Sertoli cells linked tightly by intercellular junctions and with each germ cell enshrouded by elongations of Sertoli cell cytoplasm. Spermatogenesis comprises serial stages from the mitotic replication of the stem and early germ cells, followed by meiosis, the reductive division producing haploid, amorphous gametes which subsequently undergo spermiogenesis, the metamorphosis into terminally differentiated and functional spermatozoa. Although long known that all but the earliest stages are hormonally regulated by pituitary secretion of LH and FSH, it has remained difficult to separate gonadotrophin effects by classical endocrine ablate-replace methods as these two heterodimeric hormones have identical α and homologous β subunits, are secreted from the same pituitary gonadotrophs to target cognate receptors expressed on adjacent testicular cells as equally homologous, heptahelical G-coupled protein receptors. Over two decades our laboratory has developed a variety of complementary genetic and pharmacological approaches to dissect the individual and co-operative effects of LH, its main effector testosterone and FSH on spermatogenesis. Using the gonadotrophin and testosterone deficient hpg mouse, double transgenic human FSH secreting mouse and the androgen receptor knockout mouse lines together with steroidal depot homone delivery, we have explored systematically annd defined the individual primary actions of FSH and testosterone and their interactions in the regulation of testis growth, spermatogenesis and ultimately male fertility.