Spermatogenesis: The development from stem cells to sperm and its regulation by hormones and growth factors

After introducing the stages of male germ cell development, we present the testicular somatic cell types, jointly providing indispensable structural and nutritional support as well as regulatory input during spermatogenesis. We will examine how somatic and germ cells interact to form the germinal epithelium that produces spermatozoa in the cystic mode of spermatogenesis typically found in fish (and amphibia). We discuss how endocrine signals from the pituitary and paracrine signals produced in testis tissue, often in response to endocrine signals, coordinate the cellular and molecular processes that constitute spermatogenesis. In this regard, we first discuss the mitotic phase, when proliferating spermatogonia generate the high number of germ cells required for male fertility. These cells enter meiosis, before completing final differentiation, i.e., the spermiogenesis phase and the acquisition of the spermatozoon fertility potential.