Correlative Live Imaging and Immunofluorescence for Analysis of Chromosome Segregation in Mouse Preimplantation Embryos.

Chromothripsis is a phenomenon observed in cancer cells, wherein a single or few chromosome(s) exhibit vast genomic rearrangements. Recent studies elucidated a striking series of events in which defective segregation of chromosomes causes their incorporation into micronuclei, where they are subject to extensive DNA damage prior to re-joining the main mass of chromosomes in a subsequent cell cycle, which provide an appealing mechanism for the etiology of chromothripsis. Micronuclei are well known to be common in human preimplantation embryos. We recently showed that, unlike in cancer cells, in mouse preimplantation embryos the micronuclei are maintained during multiple cell generations and apparently fail to re-join the main set of chromosomes. This unexpected finding could safeguard the early embryonic genome from chromothripsis. Here, we describe an approach that combines live and immunofluorescence imaging methods that was pivotal in that study to reveal the lack of a functional kinetochore in chromosomes from mouse embryo micronuclei.