Metaphase chromosome structure is dynamically maintained by condensin I-directed DNA (de)catenation.

Ewa Piskadlo,Raquel A Oliveira,Alexandra Tavares

doi:10.7554/elife.26120

Abstract

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.

Highlights

Mitotic chromosome assembly, poorly understood at the molecular level (Piskadlo and Oliveira, 2016), fulfils three major tasks essential for faithful chromosome segregation: First, it ensures chromosome compaction making cell division feasible within the cell space
We further demonstrate that upon condensin I cleavage previously separated sister DNA molecules undergo topoisomerase II-dependent re-intertwining and complete failure in chromosome segregation
To study the role of condensin complexes in the maintenance of chromosome structure, during metaphase, we developed a system to enable analysis of chromosomal structural changes upon rapid and temporally controlled inactivation of condensin in Drosophila melanogaster

Summary

Introduction

Poorly understood at the molecular level (Piskadlo and Oliveira, 2016), fulfils three major tasks essential for faithful chromosome segregation: First, it ensures chromosome compaction making cell division feasible within the cell space. Biochemical and phenotypic analysis of condensin depletion suggest several possible activities for these complexes, including the resolution of DNA entanglements (Gerlich et al, 2006; Hagstrom et al, 2002; Hirano, 2006; Hudson et al, 2003; Oliveira et al, 2005; Ribeiro et al, 2009; Steffensen et al, 2001) and structural integrity by conferring chromosome rigidity (Gerlich et al, 2006; Houlard et al, 2015; Oliveira et al, 2005; Ribeiro et al, 2009) Whether or not these complexes promote chromatin compaction remains controversial (Hagstrom et al, 2002; Hirano, 2006; Hirano et al, 1997; Hudson et al, 2003; Kimura and Hirano, 1997; Lavoie et al, 2002; Oliveira et al, 2005; Steffensen et al, 2001).

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