Local control mechanisms in the testis.

The gonads are unique organs in that they harbor the cells of the germline and consequently provide the local environment necessary for the normal development and differentiation of gametes. Since the local requirements for germ differentiation differ considerably from those of somatic cells the structural and physiological organization of the gonad is complex and compartmentalized. An elaborate network of local paracrine interactions between the somatic and gametogenic elements appears to be essential for normal germ cell development in mammals. This is especially true for the testis where meiosis is continuous throughout adulthood and where the spermatogenic cycle of the seminiferous epithelium is strictly controlled in time and space. The present paper reviews briefly the rapidly expanding field of testicular paracrinology. Special emphasis is given to the role of intra- and intercompartmental paracrine communication in the development of the male gamete.