Micronuclei with multiple copies of the X chromosome: do chromosomes replicate in micronuclei?

The formation of a micronucleus due to chromosome lagging is a well known mechanism of chromosomal loss. However, the post-mitotic fate of the micronucleus and the chromosomal DNA within it is poorly understood. We observed micronuclei (MN) that had multiple copies of the X chromosome (ranging from 4 to 10) when analyzing cultured human lymphocytes using fluorescence in situ hybridization (FISH). A possible mechanism for this observation is that the chromosome(s) or chromatid(s) contained within the micronuclei successfully completed one or more cycles of replication after their expulsion from the primary nucleus.