Research Papers: Chromosome:
Chromosomes missegregated into micronuclei contribute to chromosomal instability by missegregating at the next division
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Bin He1,2, Nisha Gnawali1,3, Albert W. Hinman1,2,4, Aaron J. Mattingly1,5, Alyssa Osimani2 and Daniela Cimini1,2
1 Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA
2 Biocomplexity Institute, Virginia Tech, Blacksburg, VA 24061, USA
3 Current affiliation: Orlando Health, MP 401, Orlando, FL 32819, USA
4 Current affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA
5 Current affiliation: Department of Cell and Tissue Biology, UCSF, San Francisco, CA 94122, USA
Keywords: micronucleus; Chromosome; missegregation; lagging chromosome; mitosis
Received: January 21, 2019 Accepted: March 21, 2019 Published: April 12, 2019
Micronuclei (MNi) are extranuclear DNA-containing structures that form upon mitotic exit from unsegregated chromosome fragments or anaphase lagging (whole) chromosomes (LCs). MNi formed from whole chromosomes are of particular interest because LCs are observed in both cancer and non-cancer cells, and are recognized as a major source of chromosomal instability (CIN) in cancer cells. Here, we generated a PtK1 cell line expressing a photoactivatable H2B histone to study the behavior of whole chromosome-containing MNi at the mitosis following their formation. Importantly, MNi of PtK1 cells did not display the membrane rupture or transport defects reported for other cell types. Despite this, we found that most micronucleated cells displayed some kind of chromosome segregation defect and that the missegregating chromosome was the one derived from the MN. Moreover, condensation of the chromosome within the MN was frequently delayed and associated with failure to align at the metaphase plate. Finally, the defective condensation of the MN-derived chromosomes could also explain the frequent occurrence of cytokinesis failure in micronucleated cells. In summary, we find that chromosomes from MNi may trigger a CIN phenotype by missegregating at the mitosis following MN formation.
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