Broad H3K4me3 domains support oocyte genome silencing and maturation but are dispensable for repression in early embryos

To investigate whether demethylation of broad histone H3 lysine 4 trimethyl (H3K4me3) domains is sufficient to trigger premature embryonic genome activation (EGA), we overexpressed the H3K4me3 demethylase KDM5B in mouse zygotes and early 2-cell (2C) embryos via mRNA injection. We performed single-cell RNA sequencing (scRNA-seq) using the SMART-Seq Stranded Kit (Takara Bio) on individual Kdm5b-yfp–injected and water-injected control zygotes and 2C embryos. Differential expression analysis revealed minimal transcriptional changes, and developmental stage, rather than KDM5B overexpression, accounted for most gene expression variance. Our findings demonstrate that wide-scale removal of H3K4me3 in zygotes or early 2C embryos is not sufficient to induce premature EGA, suggesting that genome silencing at these stages does not depend on broad H3K4me3 domains.