OVOL1/2 regulate trophectoderm differentiation during the morula-to-blastocyst transition

The blastocyst formation rate of human embryos cultured in vitro for assisted reproduction is approximately 50%, with most embryos arresting at the cleavage stage; however, the underlying mechanisms remain poorly understood. Here, we performed single-cell RNA sequencing of biopsied blastomeres from morphologically high-quality 8-cell embryos and tracked the developmental progression of the remaining embryos to the blastocyst stage. Embryos that failed to form blastocysts exhibited impaired zygotic genome activation (ZGA). We identified OVOL1/2 as critical ZGA genes that were markedly underactivated in these embryos. Functional analyses in both mouse and human embryos demonstrate that depletion of OVOL1/2 disrupts trophectoderm differentiation via ARPC1B-dependent mechanisms, thereby impairing the morula-to-blastocyst transition. Collectively, these findings provide mechanistic insights into preimplantation embryonic development and reveal potential causes of blastocyst formation failure.