Embryo and prejudice: From diverse first transcriptional impressions to a common developmental path

Pre-implantation mammalian development culminates in the blastocyst, where embryonic and extra-embryonic tissue founders reside. However, species variations in the underlying mechanisms, starting from zygotic genome activation (ZGA), remain underexplored. In this issue of Cell Genomics, Zhang et al.¹ studied RNA Pol II in bovine embryos and discovered super RNA Pol II domains, a regulatory architecture promoting transcription in species with delayed ZGA.