Selective cellular localization of UHRF1 safeguards mammalian zygotic genome activation and early embryonic development.

Zygotic genome activation (ZGA) is essential for initiating the developmental gene expression program in early embryos. However, whether a gating mechanism orchestrated by a limited number of factors exists in mammals remains debated. In this study, by utilizing an Nlrp14-deficient model that intriguingly disrupts the zygotic localization of UHRF1 and DNMT1, and in combination with comprehensive genetic approaches, we demonstrated that the nuclear exclusion of UHRF1 is essential for mouse ZGA and subsequent developmental progression. Mechanistically, the failure to exclude UHRF1 and DNMT1 from the nucleus in zygotes would impede DNA demethylation in LINE1 elements, promote UHRF1 binding to silence their expression, thereby reducing global chromatin accessibility and inhibiting ZGA. This effect was rescued in Uhrf1/Nlrp14 double knockout (DKO) embryos, which still exhibited heavy DNA methylation, highlighting a dispensable role of UHRF1 in the maintenance of genome-wide DNA methylation after fertilization. Furthermore, reducing DNA methylation through Dnmt1/Nlrp14 DKO or inhibiting the DNA methylation-binding domains of UHRF1 mitigated the adverse effects of nuclear-localized UHRF1 and reactivated the ZGA genes. Finally, we demonstrated that the residual nuclear UHRF1 in normal embryos binds to and facilitates the transcriptional inactivation of specific LTR subtypes that evade DNA demethylation during the genome-wide epigenetic reprogramming. Our findings not only highlight the biological significance of UHRF1 and DNMT1 nuclear exclusion but also elucidate the potentially conserved mechanism that regulates ZGA during mammalian preimplantation development.