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Updated: Aug 7, 2026

Chromatin Spread Preparations for the Analysis of Mouse Oocyte Progression from Prophase to Metaphase II
Published on: February 26, 2018
Premitotic chromosome individualization in mammalian cells depends on topoisomerase II activity
J F Giménez-Abián1, D J Clarke, J Devlin
1Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
Abstract:
When DNA topoisomerase II (topo II) activity is inhibited with a non-DNA-damaging topo II inhibitor (ICRF-193), mammalian cells become checkpoint arrested in G2-phase. In this study, we analyzed chromosome structure in cells that bypassed this checkpoint. We observed a novel type of chromosome aberration, which we call omega-figures. These are entangled chromosome regions that indicate the persistence of catenations between nonhomologous sequences. The number of omega-figures per cell increased sharply as cells evaded the transient block imposed by the topo II-dependent checkpoint, and the presence of caffeine (a checkpoint-evading agent) potentiated this increase. Thus, the removal of nonreplicative catenations, a process that promotes chromosome individualization in G2, may be monitored by the topo II-dependent checkpoint in mammals.
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