Abstract
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.