During the last 5 years significant advances have been achieved in defining the endocrine, paracrine and cellular interactions required for normal testicular development. Numerous paracrine factors are likely to regulate spermatogenesis throughout the cycle of the seminiferous epithelium. These factors create the local hormonal milieu required for germ cell proliferation, meiosis and differentiation. The studies of the c-kit oncogene and the stem cell growth factor in the migration and survival of the primordial germ cells to the genital ridge during development have defined at least 1 important role of growth factors in spermatogenesis. 72, 142-146, 148, 149, 154, 159 It is likely that in the next 5 years the role of many of these other paracrine factors in the regulation of testicular development will be determined.
