Evidence that activin A directly modulates early human male germline differentiation status

Disrupted fetal germline development underpins testicular germ cell neoplasia, which is increasing worldwide. The complex signaling milieu during normal testis development includes TGFβ superfamily ligands; this study tests the hypothesis that, activin A, a TGFβ superfamily member, can influence gonocyte development. The human seminoma-derived cell line, TCam-2, a model of fetal gonocytes, was cultured with activin A (1.25-25 ng/mL) for 48 h, or with 5 ng/mL activin A for short- (6, 24, and 48 h) and long-term (13 days) exposures, and downstream targets measured by qRT-PCR. Transcripts that exhibited significant dose-dependent responses to activin A included the early germ cell markers KIT, NODAL, and CRIPTO (NODALl co-receptor and activin inhibitor) which all increased and the differentiation marker DNMT3L which decreased. After 48 h, KIT, NODAL, and CRIPTO levels were significantly higher, while the differentiation marker NANOS2 was significantly lower. Interestingly, activin A exposure also significantly reduced both transcript and protein levels of the PIWI/piRNA pathway component DNMT3L. Because TCam-2 cells produce the activin inhibitor CRIPTO, CRIPTO was reduced using siRNA prior to activin A exposure. This selectively increased KIT in response to activin A. Other ligands present in the fetal testis (BMP4, FGF9, TGFβ1, and TGFβ2) induced distinct effects on germline marker expression. This study showed that activin A can directly modulate germline markers in this human gonocyte-like cell, promoting a less-differentiated phenotype. Additional findings indicate evidence of signaling crosstalk between activin A and NODAL, leading to target-specific effects on gonocyte differentiation.