OBOX regulates murine zygotic genome activation and early development

Zygotic genome activation (ZGA) activates the quiescent genome to enable the maternal-to-zygotic transition. However, the identity of transcription factors (TFs) that underlie mammalian ZGA in vivo remains unresolved. Here, we showed that OBOX, a PRD-like homeobox domain TF family that includes 66 members (OBOX1-8), are key regulators of mouse ZGA. Knockout mice deficient for maternally transcribed Obox1/2/5/7 and zygotically expressed Obox3/4 led to 2-4 cell arrest accompanied by impaired ZGA. Maternal and zygotic expressed OBOX redundantly support embryonic development as Obox KO defects can be rescued by restoring either of them. Chromatin binding analysis revealed Obox knockout preferentially affected OBOX-binding targets. Mechanistically, OBOX facilitated RNA Pol II ?pre-configuration?, as Pol II relocates from the initial 1-cell binding targets to ZGA gene promoters and distal enhancers. The impaired Pol II pre-configuration in Obox mutants was accompanied by downregulation of ZGA genes, chromatin accessibility transition defects, as well as aberrant activation of one-cell Pol II targets. Finally, OBOX ectopically activated ZGA genes and MERVL in mESCs. Hence, these data demonstrate that OBOX regulates murine ZGA and early embryogenesis. By employing RNA-seq and Pol II Stacc-seq/ATAC-Seq in Obox mzKO embryos as well as RNA-seq in Obox OE mESCs, we revealed maternal OBOX is the key transcription factor regulating murine zygotic genome activation.