| Summary: | 博士 === 國立陽明大學 === 生化暨分子生物研究所 === 102 === Primordial germ cells (PGCs) are derived from epiblast cells at early stage of embryogenesis, escaped from the somatic program of differentiation after exposure to extraembryonic signals in mouse and human. Prdm1 is regarded as a determinant that specified the mouse germ cell fate. However, the underlying mechanism of human PGC determination and differentiation is still unclear. Here, we showed that PRDM1 positive cells were identified in human fetal gonads, represented as the early-stage germ cells because they showed the co-localization with OCT4, not with post-migration marker VASA and meiotic marker SCP3. Using human embryonic stem cells (hESCs) as an in vitro model of PGCs differentiation, we found that PRDM1 was co-expressed with OCT4 in putative PGCs, consistent with the previous findings in vivo. Next, We demonstrated that PRDM1 is necessary for BMP4 and WNT3A signaling in promoting germ cell differentiation. In contrast, knockdown of PRDM1 blocked the effect of BMP4 and WNT3A and impeded germ cell differentiation. Ectopic PRDM1 expression improved the effect of BMP4 and WNT3A-induced germ cell differentiation. Ectopic expression of PRDM1 in hESCs up-regulated several germ cell markers and re-established the gene expression profiles that is highly correlated to human fetal gonads. In addition, hESCs showed reciprocal expression of PRDM1 and SOX2. We found PRDM1 binds directly to SOX2 promoters and repressed its expression. SOX2 overexpression was sufficient to induce neuronal differentiation in BMP4 and WNT3A treated hESCs. In conclusion, we showed that PRDM1, a transcriptional repressor, directly suppressed SOX2 expression in order to prevent the activation of neuronal differentiation, and facilitated germ cell differentiation. These findings revealed that repression of SOX2 is fundamental for PRDM1 to control germ cell differentiation, also provided a new insight into human germ cell differentiation in vitro.
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