| Gonocytes are precursors of spermatogonia, stem cells of the germ lineage. Their maturation involves proliferation, migration to the seminiferous cord's basement membrane and differentiation into spermatogonia. We previously showed that in vitro proliferation of neonatal (dpp3) gonocytes is induced by Platelet-Derived Growth Factor (PDGF) and Estradiol (E2) in a non-additive manner. The present work extends these findings with two aims: (1) uncover the mechanisms regulating neonatal gonocyte proliferation; (2) study the impact of in utero exposure to environmental estrogens on testis development.; In aim1, we identified elements of PDGF and E2 signaling pathways and examined their role in proliferation using activators and inhibitors on isolated gonocytes. We found that PDGF signal transduction involved PDGF receptor (PDGFR), Raf1 and MEK/ERK proteins, while E2 signaled through its receptor. We also showed that the two pathways were interdependent as proliferation occurred only when both were activated.; In aim2, we examined the effect of in utero exposure to the environmental estrogens Genistein, Coumestrol and Bisphenol A, using the estrogen Diethylstilbestrol as a control; and evaluated testicular development. At dpp3, the main effect was an increase in PDGFRs mRNA and protein levels. However, our results also revealed differences in the effects of each compound. We also found that in vivo dpp3 gonocyte proliferation was reduced by the treatments, even at lower doses. Morphometric analysis showed that the volume of the spermatogonia population was increased in prepubertal testis (dpp21). Adult testis (dpp60) displayed normal germ cell volumes but an increased Leydig cell population volume, even at low doses. We also tested the ability of the compounds to induce gonocyte proliferation in vitro: Genistein, BPA and DES induced a high proliferation rate at pM concentration, while the minimal efficient dose of E2 was nM. Interestingly, combined fM doses of Genistein and BPA induced proliferation as well.; In conclusion, environmental estrogens are more potent that estradiol on normal cell proliferation and may have synergistic capabilities. This suggests that current levels of environmental estrogen exposure may pose a threat to a fetus, since they temporarily alter testis development and may induce a long lasting effect on Leydig cell volume, potentially increasing the risk of testicular cancer. |
