In the Figure (left to right); i) cartoon representing the Rabl configuration of chromosomes in the early embryo. Pericentromeric regions are apical, chromosome arms are aligned and telomeres are basal. A-compartments are represented in yellow and B-compartments are represented in blue. ii) Immunofluorescence staining for HP1a in early embryo, reflecting the Rabl configuration as in the cartoon, with HP1 enrichment in pericentromeric regions. iii) Differential Hi-C contact map (log2-transformed), highlighting increased contact frequencies within chromosome arms, decreased inter-arm and inter-chromosome contacts, reduced associations within and between pericentromeric regions in HP1-KD embryos. iv) Snapshots of polymer simulations of chromatin folding in wild-type control (left) and mutant (right) conditions, where the pericentromeric regions are free to expand.