Feed-forward loops by NR5A2 ensure robust gene activation during pre-implantation development.

Pioneer transcription factors are crucial for regulating zygotic genome activation and cell differentiation during mouse pre-implantation development. However, how pioneer factors function collectively to regulate early development remains poorly understood. Here, we determined the chromatin-binding profiles of the mouse pioneer factor NR5A2 during the totipotency-to-pluripotency transition and identified KLF and GATA family transcription factors as key co-regulators. NR5A2 regulates the expression of Klf5 and Gata6, the protein products of which in turn act as co-regulators of NR5A2 to promote development. Mechanistically, KLF5 contributes to H3K27ac deposition at genomic regions co-occupied by NR5A2. NR5A2 also regulates Xist expression, either directly or indirectly, through its role in co-binding with GATA factors and upregulating their expression. In vitro assays revealed that NR5A2 binds to nucleosomes with KLF5 and GATA6, suggesting that these pioneer factors can simultaneously bind to chromatin. Our findings provide evidence for a feed-forward regulatory mechanism by which NR5A2 activates expression of lineage-determining factors and these, together with NR5A2, subsequently co-bind nucleosomes to ensure robust gene activation during pre-implantation development.