Undifferentiated primate spermatogonia and their endocrine control

The biology of spermatogonial stem cells is currently an area of intensive research and contemporary studies in primates are emerging. Quantitative regulation of sperm output by the primate testis seems to be exerted primarily on the transition from undifferentiated to differentiating spermatogonia. This review examines recent advances in our understanding of the mechanisms governing spermatogonial renewal and early differentiation in male primates, with a focus on the monkey. Emerging revisions to the classic view of dark and pale type A spermatogonia as reserve and renewing spermatogonial stem cells, respectively, are critically evaluated and essential features of endocrine control of undifferentiated spermatogonia throughout postnatal primate development are discussed. Obstacles in gaining a more complete understanding of primate spermatogonia are also identified.