Recurrent Micronucleation through Cell Cycle Progression in the Presence of Microtubule Inhibitors

Abstract

ABSTRACT. Although most cell lines undergo mitotic arrest after prolonged exposure to microtubule inhibitors, some cells subsequently exit this state and become tetraploid. Among these cells, limited numbers of rodent cells are known to undergo multinucleation to generate multiple small independent nuclei, or micronuclei by prolonged colcemid treatment. Micronuclei are thought to be formed when cells shift to a pseudo G1 phase, during which the onset of chromosomal decondensation allows individual chromosomes distributed throughout the cell to serve as sites for the reassembly of nuclear membranes. To better define this process, we used longterm live cell imaging to observe micronucleation induced in mouse A9 cells by treating with the microtubule inhibitor colcemid. Our observations confirm that nuclear envelope formation occurs when mitotic-arrested cells shift to a pseudo G1 phase and adopt a tetraploid state, accompanied by chromosome decondensation. Unexpectedly, only a small number of cells containing large micronuclei were formed. We found that tetraploid micronucleated cells proceeded through an additional cell cycle, shifting to a pseudo G1 phase and forming octoploid micronucleated cells that were smaller and more numerous compared with the tetraploid micronucleated cells. Our data suggest that micronucleation occur when cells shift from mitotic arrest to a pseudo G1 phase, and demonstrate that, rather than being a single event, micronucleation is an inducible recurrent process that leads to the formation of progressively smaller and more numerous micronuclei.

N-(2-methyl-indol-1H-5-yl)-1-naphthalenesulfonamide: A novel reversible antimitotic agent inhibiting cancer cell motility

“…Interestingly, in correlation with the effects of other established tubulin binders [27], long term treatment (>48h) with 8e also induced micronucleation ( Figure 6C). We finally investigated whether 8e could directly influence tubulin polymerization in vitro.…”

Moving toward a higher efficiency of microcell-mediated chromosome transfer

“…Unlike most cell lines, which die under prolong exposure to microtubule inhibitors, the A9 and CHO cells undergo repetitive hyperploidization in the presence of Colcemid with micronucleation occurring during the transition from metaphase to pseudo-G1. 2 Micronuclei formed by A9 and CHO are thus smaller and more numerous. These micronuclei can subsequently be extruded from the cell as microcells by centrifugation in the presence of cytoskeleton disruptor, like an actin inhibitor.…”

Antiproliferative Fate of the Tetraploid Formed after Mitotic Slippage and Its Promotion; A Novel Target for Cancer Therapy Based on Microtubule Poisons

“…The other type of alteration yields multinuclei, a cluster of mis-segregated uncondensed chromosomes. We explain the similarities and differences between these two types of nuclear alteration, and describe a potentially new intermediate type observed in our recent study (clustered micronuclei) [9,10].…”

“…Both micronuclei and multinuclei are nuclear alterations characterizing mitotic catastrophe. Recently, we reported a possible new type of micronuclei [10], and refer to it as ‘clustered micronuclei’ in this review. We provide an overview of clustered micronuclei with its oncosuppressive features.…”