The α isoform of topoisomerase II is required for hypercompaction of mitotic chromosomes in human cells.
As proliferating cells transit from interphase into M-phase, chromatin undergoes extensive reorganization, and topoisomerase (topo) IIα, the major isoform of this enzyme present in cycling vertebrate cells, plays a key role in this process. In this study, a human cell line conditional null mutant for topo IIα and a derivative expressing an auxin-inducible degron (AID)-tagged version of the protein have been used to distinguish real mitotic chromosome functions of topo IIα from its more general role in DNA metabolism and to investigate whether topo IIβ makes any contribution to mitotic chromosome formation. We show that topo IIβ does contribute, with endogenous levels being sufficient for the initial stages of axial shortening. However, a significant effect of topo IIα depletion, seen with or without the co-depletion of topo IIβ, is the failure of chromosomes to hypercompact when delayed in M-phase. This requires much higher levels of topo II protein and is impaired by drugs or mutations that affect enzyme activity. A prolonged delay at the G2/M border results in hyperefficient axial shortening, a process that is topo IIα-dependent. Rapid depletion of topo IIα has allowed us to show that its function during late G2 and M-phase is truly required for shaping mitotic chromosomes.
Department of Genetics, University of Cambridge, Downing St, Cambridge CB2 3EH, UK and Centre for Haematology, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Rd, London W12 0NN, UK.
Christine J
CJ
Farr
Melissa
M
Antoniou-Kourounioti
Michael L
ML
Mimmack
Arsen
A
Volkov
Andrew C G
AC
Porter
D000951:Antigens, Neoplasm / Q000235:genetics / Q000502:physiology*; D020134:Catalytic Domain; D002460:Cell Line; D002877:Chromosomes, Human; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D016195:G2 Phase / Q000235:genetics; D006801:Humans; D008938:Mitosis / Q000235:genetics*; D009154:Mutation; D020033:Protein Isoforms / Q000037:antagonists & inhibitors; D011804:Quinolines / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D020033:Protein Isoforms; D011804:Quinolines; C512984:RO 3306; D013844:Thiazoles; D004250:DNA Topoisomerases, Type II