Nucleation-dependent propagation of Polycomb modifications emerges during the <i>Drosophila</i> maternal to zygotic transition

During zygotic genome activation in Drosophila , broad domains of Polycomb-modified chromatin are rapidly established across the genome. Here, we investigate the spatial and temporal dynamics by which Polycomb group (PcG) histone modifications, H3K27me3 and H2Aub, emerge during early embryogenesis. Using ChIP-seq and live imaging of CRISPR-engineered GFP-tagged PcG components, we show that…