The regulation of germ cell proliferation in the prepubertal marmoset testis : towards a strategy for fertility preservation in boys treated for cancer

Immunohistochemistry was used on Bouins-fixed marmoset testes from birth to adulthood, including tissue from males treated prepubertally for ten weeks with a GnRH antagonist, to elucidate the role of gonadotrophins. No difference was found between germ cells from control and GNRH antagonist-treated animals in the immunoexpression of MAGE, a germ cell-specific marker, Ki67, a marker of cell proliferation, and Histone H3, a marker of cell mitosis, confirming that spermatogonial proliferation is gonadotrophin-independent. To determine potential regulators, spermatogonial immunoexpression of growth factor receptors was investigated. Receptors for several growth factors were identified in spermatogonia. The expression of receptors for both epidermal Growth Factor and Neurturin was pronounced in a proportion of germ cells in late infancy, thus implicating a role for these factors in spermatogonial development. Prepubertal expression of these receptors was unaffected by prior treatment with a GnRH antagonist, demonstrating their gonadotrophin independence. Studies using confocal microscopy demonstrated that the spermatogonial population expressing these receptors were not actively proliferating, raising the possibility that these factors act to inhibit proliferation. Manipulation of these factors may protect fertility in boys treated for cancer. As survival of stem spermatogonia is essential for future fertility, this study also attempted to identify a marker of stem cells in the primate, in order to investigate their activity prepubertally. GFR-α1, the receptor for Glial Cell Line-Derived Neurotrophic Factor, is expressed by A-spermatogonia in the mouse. In marmoset testis, expression of this receptor was shown in occasional germ cells, in a pattern consistent with stem cells, at all ages studied. Attempts to co-localise GFR-α1 with cell cycle markers suggest these cells are not actively proliferating.