Chromatin remodeling in bovine embryos indicates species-specific regulation of genome activation

The maternal-to-zygotic transition (MZT) is underpinned by wide-spread transcriptomic and epigenomic remodeling that facilitates totipotency acquisition. Factors regulating MZT vary across species and differences in timing of developmental transitions and motif enrichment at accessible chromatin between human and mouse embryos suggest a distinct regulatory circuitry. Profiling accessible chromatin in bovine preimplantation embryos—timing of developmental transitions in bovine closely resembles that in human—indicated that prior to embryonic genome activation (EGA) accessible chromatin is enriched in maternal transcription factor recognition sites, e.g., CTCF, KLFs, NFY, and SP1, echoing observations in humans and mice, and suggesting that a conserved set of maternal factors regulate chromatin remodeling prior to EGA. In contrast, open chromatin established during EGA was primarily enriched for homeobox motifs and showed remarkable similarities between cattle and humans, indicating that cattle could be a more relevant model for human preimplantation development than mice.