SETDB1 is essential for mouse primordial germ cell fate determination by ensuring BMP signaling.

In mouse embryos, primordial germ cells (PGCs) are fate-determined from epiblast cells. Signaling pathways involved in PGC formation have been identified, but their epigenetic mechanisms remain poorly understood. Here, we show that the histone methyltransferase SETDB1 is an epigenetic regulator of PGC fate determination. Setdb1-deficient embryos exhibit drastic reduction of nascent PGCs. Dppa2, Otx2 and Utf1 are de-repressed whereas mesoderm development-related genes, including BMP4 signaling-related genes, are downregulated by Setdb1 knockdown during PGC-like cell (PGCLC) induction. In addition, binding of SETDB1 is observed at the flanking regions of Dppa2, Otx2 and Utf1 in cell aggregates containing PGCLCs, and trimethylation of lysine 9 of histone H3 is reduced by Setdb1 knockdown at those regions. Furthermore, DPPA2, OTX2 and UTF1 binding is increased in genes encoding BMP4 signaling-related proteins, including SMAD1. Finally, overexpression of Dppa2, Otx2 and Utf1 in cell aggregates containing PGCLCs results in the repression of BMP4 signaling-related genes and PGC determinant genes. We propose that the localization of SETDB1 to Dppa2, Otx2 and Utf1, and subsequent repression of their expression, are crucial for PGC determination by ensuring BMP4 signaling.