Rules of engagement for condensins and cohesins guide mitotic chromosome formation

Data from "Rules of engagement for condensins and cohesins guide mitotic chromosome formation". Kumiko Samejima, Johan H. Gibcus, Sameer Abraham, Fernanda Cisneros-Soberanis, Itaru Samejima, Alison J. Beckett, Nina Pučeková, Maria Alba Abad, Bethan Medina-Pritchard, James R. Paulson, Linfeng Xie, A. Arockia Jeyaprakash, Ian A. Prior, Leonid A. Mirny, Job Dekker, Anton Goloborodko, William C. Earnshaw. bioRxiv 2024.04.18.590027. https://doi.org/10.1101/2024.04.18.590027. We used Hi-C, imaging, proteomics and polymer modeling to define rules of engagement for SMC complexes as cells refold interphase chromatin into rod-shaped mitotic chromosomes. Firstly, condensin disassembles interphase chromatin loop organization by evicting or displacing extrusive cohesin. Secondly, condensin bypasses cohesive cohesins, thereby maintaining sister chromatid cohesion as sisters separate. Studies of mitotic chromosomes formed by cohesin, condensin II and condensin I alone or in combination reveal new models of mitotic chromosome conformation. In these models, loops are consecutive and not overlapping, implying that condensins stall upon encountering each other. The dynamics of Hi-C interactions and chromosome morphology reveal that during prophase loops are extruded in vivo at ~1-3 kb/sec by condensins as they form a disordered discontinuous helical scaffold within individual chromatids.