Macro, micro, and molecular research on spermatogenesis: the quest to understand its control

Synchronous maturation of the germ cells in the seminiferous epithelium has long been recognized by microscopy, and is believed to be a consequence of a complex interaction between the germ cells and the Sertoli cells, largely driven by testosterone and its synergistic action with follicle-stimulating hormone. Overall coordination of the cycle of the seminiferous epithelium is reviewed with regard to the known and possible actions of testosterone upon the Sertoli cells and the germ cells. With gradual refinements of optical instrumentation and development of a wide range of histological, morphometric, biochemical, and molecular techniques, coupled with selective alterations of hormonal stimulation and the cellular composition of the testis, new approaches to the question of how sperm production is regulated are becoming available. Germ cell and Sertoli cell functions are intimately related to each other via local, intratesticular or paracrine signals which are suppressed or triggered at certain defined steps in the spermatogenic process. The coordination of germ cell proliferation and maturation is discussed in terms of the contributions made by microscopical techniques.