Piskadlo, EwaTavares, AlexandraOliveira, Raquel A2018-01-312018-01-312017-05-06eLife 2017;6:e26120 doi: 10.7554/eLife.26120http://hdl.handle.net/10400.7/826This deposit is composed by the main article and the supplementary materials are present in the publisher's page in the following link: https://elifesciences.org/articles/26120/figures.Mitotic chromosome assembly remains a big mystery in biology. Condensin complexes are pivotal for chromosome architecture yet how they shape mitotic chromatin remains unknown. Using acute inactivation approaches and live-cell imaging in Drosophila embryos, we dissect the role of condensin I in the maintenance of mitotic chromosome structure with unprecedented temporal resolution. Removal of condensin I from pre-established chromosomes results in rapid disassembly of centromeric regions while most chromatin mass undergoes hyper-compaction. This is accompanied by drastic changes in the degree of sister chromatid intertwines. While wild-type metaphase chromosomes display residual levels of catenations, upon timely removal of condensin I, chromosomes present high levels of de novo Topoisomerase II (TopoII)-dependent re-entanglements, and complete failure in chromosome segregation. TopoII is thus capable of re-intertwining previously separated DNA molecules and condensin I continuously required to counteract this erroneous activity. We propose that maintenance of chromosome resolution is a highly dynamic bidirectional process.engDrosophila melanogastercell biologychromosome condensationcondensinmitosistopoisomerasejournal article10.7554/eLife.26120