Zygotic genome activation (ZGA) is the point at which the embryo stops relying on maternally deposited transcripts and transcription of the embryonic genome begins. In mice, ZGA occurs at the two-cell stage and two-cell (2C)-like embryonic stem cells have been used as an in vitro model to study ZGA. Previous studies using 2C-like cells have identified developmental pluripotency-associated 2 and 4 (DPPA2 and DPPA4) as crucial regulators of ZGA upstream of the DUX transcription factor. However, two independent studies in this issue reveal that the role of DPPA2 and DPPA4 is dispensable for ZGA in vivo. Yi Zhang and colleagues generate single maternal knockout and maternal-zygotic knockout mice for Dppa2 and Dppa4. Similarly, Melanie Eckersley Maslin and colleagues produce single and double maternal knockouts for Dppa2 and/or Dppa4, as well as Dppa4 maternal-zygotic knockouts. Using these lines, the authors show that DPPA2 and DPPA4 are not required for pre-implantation development, with mutant embryos developing into blastocysts. Using whole-embryo RNA sequencing of two-cell mutant embryos, they show that DPPA2 and DPPA4 are not required for Dux expression and ZGA. Although dispensable for pre-implantation development, the researchers show that both maternal and zygotic Dppa2 and Dppa4 are required for post-implantation development and offspring survival. Taken together, these studies support the dispensable role of DPPA2 and DPPA4 for ZGA reproducibly, and highlight the validity of testing results from 2C-like embryonic stem cells in vivo.
