The   isoform of topoisomerase II is required for hypercompaction of mitotic chromosomes in human cells

Abstract

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.

Disruption of a Conserved CAP-D3 Threonine Alters Condensin Loading on Mitotic Chromosomes Leading to Chromosome Hypercondensation

“…Our results therefore agree with experiments using Xenopus egg extracts in a cell-free system, which show the relative ratio of condensin I to II is one of the key determinants in shaping mitotic chromosomes (45). Topoisomerase II␣ (Topo II␣) is another scaffold protein involved in the axial shortening of chromosomes and is dependent on condensin for correct localization (40,46). Abnormal Topo II␣ activity might therefore be responsible for the excessive shortening of the mitotic axes seen in CAP-D3 T1403A chromosomes.…”

SCFTIR1/AFB-Based Auxin Perception: Mechanism and Role in Plant Growth and Development

“…This system is called the auxininducible degron system (Nishimura et al, 2009;Holland et al, 2012;Kanke et al, 2012;Farr et al, 2014;Nishimura and Kanemaki, 2014;Samejima et al, 2014). All eukaryotes possess SCF ubiquitin ligases, and the architecture of Arabidopsis TIR1, including the F-box domain, is sufficiently conserved to allow assembly into an SCF TIR1 complex in yeast and animals.…”

Histone H2A phosphorylation recruits topoisomerase II α to centromeres to safeguard genomic stability

“…Though TOP2A preferentially accumulates at mitotic centromeres, it is also found on chromosome arms throughout mitosis where it may play a role in chromosome organization Gasser et al, 1986;Meyer et al, 1997;Samejima et al, 2012;Lane et al, 2013;Farr et al, 2014).…”