RNA polymerase II is necessary for spatial chromatin reorganization following exit from mitosis [Cut&Tag-seq]

Mammalian chromosomes are three-dimensional entities shaped by converging and opposing forces acting on chromatin. Mitotic cell division induces drastic chromatin condensation, but following reentry into the G1 cell cycle phase, condensed chromosomes unwind to re-establish interphase organization. Here, we use a cell line allowing auxin-mediated degradation of RNA polymerase II to test its role in this transition. In situ Hi-C and super-resolution imaging showed that RNAPII is required for compartment and loop formation following mitosis. RNAPs also often counteract loop extrusion and, in their absence, longer and more prominent loops arise. Evidence from chromatin fractionation and in silico modeling attribute these effects to RNAPII-mediated cohesin loading at active promoters upon G1 reentry. Our findings reconcile the role of RNAPII in gene expression with that in chromatin architecture. Genome-wide binding profiles for the CTCF, SMC1A and rad21 were investigated in DLD1 cells