Selective compartmentalization in condensin-depleted mitotic chromosomes [ChIP-seq II]

During mitosis, condensin activity is thought to disrupt interphase chromatin structures. Here, we utilize condensin-deficient mitotic chromosomes as a unique architectural platform to further investigate genome folding principles. Upon condensin loss, compartments progressively emerge in mitotic chromosomes. Euchromatin diverges into two different compartments A1 and A2, the former of which shows strong homotypic interactions while the latter exhibit reduced self-aggregation. Constitutive heterochromatin (B1) displays reduced level of compartmentalization and the normally inert facultative heterochromatin (B2) participates to compartmentalize the genome. Dynamically, A1 compartment is established remarkably fast with similarly efficient separation from B1 while reformation of B1 is delayed, implying that A1 self-attraction is the engine to compartmentalizalize the condensin-depleted mitotic chromosomes. Notified by the mitotic compartmentalization of B1 which lacks HP1 binding, we sought to explore the role of HP1 proteins in genome folding and demonstrat that HP1?&? are dispensible for chromatin structural restoration during cell divison. Our observations unveil delicate patterns and novel principles of genome compartmentalization that are otherwise hidden in interphase cells. Overall design: G1E-ER4:SMC2-mAID-mCherry cells were arrested to mitosis with nocodazole (200ng/ml) for 12 hours. Asynchronous cells were processed as controls