The Cycle of Kinetochore-Negative Micronuclei and Chromosome Fragments Occurred in Mitosis of Hela Cells

Abstract

Objective: Micronuclei (MNi) are extensively used to evaluate genotoxic effects and chromosome instability. According to the presence of kinetochores or not, MNi are further classified into kinetochore-negative MNi (K−MNi) and kinetochore-positive MNi (K+MNi), which show the different mechanisms of micronucleus formation. However, the differences in fates of K−MNi and K+MNi have not been completely addressed. The present study aims to address these questions. Methods: Here, HeLa CENP B-GFP H2B-mCherry cells were chosen to distinguish K+MNi and K−MNi in living cells. In the cells, MNi were identified by H2B-mCherry and further classified into K+MNi and K−MNi, i.e. the K+MNi contained CENP B-GFP, while the K−MNi did not. Long-term live-cell imaging was applied in the cells to record the dynamics of cell mitosis, especially K+MNi and K−MNi. Results: Our results show that the presence of K−MN or K+MN did not result in multipolar mitosis. K−MN-bearing cells produced much more chromosome fragments than did MN-free cells. Most of the chromosome fragments eventually merged into K−MNi. K+MN-bearing cells yielded more kinetochore-positive lagging chromosomes (K+LCs) and K+MNi than MN-free cells did. Conclusion: The results suggested the differences in the fates of K+MNi and K−MNi in mitosis. The cycle of K− MN → Chromosome fragment → K−MN may occur in generations of K−MN-bearing cells, while part of K+MNi might reincorporate into the main nucleus.