No abstract

We previously found that platelet-derived growth factor (PDGF) and 17beta-estradiol stimulate gonocyte proliferation in a dose-dependent, nonadditive manner. In the present study, we report that gonocytes express RAF1, MAP2K1, and MAPK1/3. Inhibition of RAF1 and MAP2K1/2, but not phosphoinositide-3-kinase, blocked PDGF-induced proliferation. AG-370, an inhibitor of PDGF receptor kinase activity, suppressed not only PDGF-induced proliferation but also that induced by 17beta-estradiol. In addition, RAF1 and MAP2K1/2 inhibitors blocked 17beta-estradiol-activated proliferation. The estrogen receptor antagonist ICI 182780 inhibited both the effects of 17beta-estradiol and PDGF. PDGF lost its stimulatory effect when steroid-depleted serum or no serum was used. Similarly, 17beta-estradiol did not induce gonocyte proliferation in the absence of PDGF. The xenoestrogens genistein, bisphenol A, and DES, but not coumestrol, stimulated gonocyte proliferation in a dose-dependent and PDGF-dependent manner similarly to 17beta-estradiol. Their effects were blocked by ICI 182780, suggesting that they act via the estrogen receptor. AG-370 blocked genistein and bisphenol A effects, demonstrating their requirement of PDGF receptor activation in a manner similar to 17beta-estradiol. These results demonstrate the interdependence of PDGF and estrogen pathways in stimulating in vitro gonocyte proliferation, suggesting that this critical step in gonocyte development might be regulated in vivo by the coordinated action of PDGF and estrogen. Thus, the inappropriate exposure of gonocytes to xenoestrogens might disrupt the crosstalk between the two pathways and potentially interfere with gonocyte development.

The implementation of a multipronged intervention strategy to control the outbreak of CDI significantly improved the overall situation at the hospital and underlined the importance of investing in stringent infection control practices.

Neonatal gonocytes are direct precursors of spermatogonial stem cells, the cell pool that supports spermatogenesis. Although unipotent in vivo, gonocytes express pluripotency genes common with embryonic stem cells. Previously, we found that all-trans retinoic acid (RA) induced the expression of differentiation markers and a truncated form of platelet-derived growth factor receptor (PDGFR)β in rat gonocytes, as well as in F9 mouse embryonal carcinoma cells, an embryonic stem cell-surrogate that expresses somatic lineage markers in response to RA. The present study is focused on identifying the signaling pathways involved in RA-induced gonocyte and F9 cell differentiation. Mitogen-activated protein kinase kinase (MEK) 1/2 activation was required during F9 cell differentiation towards somatic lineage, whereas its inhibition potentiated RA-induced Stra8 expression, suggesting that MEK1/2 acts as a lineage specification switch in F9 cells. In both cell types, RA increased the expression of the spermatogonial/premeiotic marker Stra8, which is in line with F9 cells being at a stage before somatic-germline lineage specification. Inhibiting PDGFR kinase activity reduced RA-induced Stra8 expression. Interestingly, RA increased the expression of PDGFRα variant forms in both cell types. Together, these results suggest a potential cross talk between RA and PDGFR signaling pathways in cell differentiation. RA receptor-α inhibition partially reduced RA effects on Stra8 in gonocytes, indicating that RA acts in part via RA receptor-α. RA-induced gonocyte differentiation was significantly reduced by inhibiting SRC (v-src avian sarcoma [Schmidt-Ruppin A-2] viral oncogene) and JAK2/STAT5 (Janus kinase 2/signal transducer and activator of transcription 5) activities, implying that these signaling molecules play a role in gonocyte differentiation. These results suggest that gonocyte and F9 cell differentiation is regulated via cross talk between RA and PDGFRs using different downstream pathways.