Work

Functional stability of the second mitotic spindle in blastomeres and its association with multinucleation repair

Year: 2025

Type: article

Abstract: OBJECTIVE: To study mitotic spindle morphology and chromosomal segregation in second mitosis. DESIGN: Live-cell imaging of deoxyribonucleic acid (DNA) and tubulin during the second mitosis of 21 freeze-thawed human two-pronuclear stage embryos was performed to analyze spindle morphology and chromosome segregation dynamics. Furthermore, chromosomal aneuploidy was assessed in all cells of the embryos that developed to the blastocyst stage. SUBJECTS: Twenty-one freeze-thawed human two-pronuclear embryos. EXPOSURE: We analyzed live-imaging videos of DNA and microtubules during the second division of 21 human 2-cell embryonic blastomeres. We further analyzed the association between the results of preimplantation genetic testing for aneuploidy of all cells in the observed embryos after development into blastocysts and the nuclear status at the early embryonic stage. MAIN OUTCOME MEASURES: Spindle morphology during the second mitosis, chromosomal segregation patterns, nuclear status of daughter blastomeres, and chromosomal aneuploidy of all cells in blastocysts derived from the observed embryos. RESULTS: Multinucleation rate in daughter nuclei was significantly lower after the second than after the first mitosis (22% vs. 56%). Neither defocusing of spindle poles-which was prominent in the first mitosis-nor chromosomal segregation abnormalities, such as misalignment of metaphase chromosomes and lagging chromosomes during chromosomal segregation, were observed. There was no association between the nuclear status at the 2- and 4-cell stages of the observed embryos that had progressed to the blastocyst stage and the preimplantation genetic testing for aneuploidy results of all cells in the blastocysts. CONCLUSION: Observations of mitotic spindle morphology and chromosomal segregation behavior revealed that second mitosis is less prone to chromosomal segregation errors than first mitosis. This suggests that segregation errors occurring during the first mitosis may be corrected during the second mitosis. Furthermore, there was no association between the nuclear status during early embryonic divisions and the chromosomal status of blastocyst cells, suggesting the presence of a mechanism that corrects chromosomal abnormalities during early development.

Source: F&S Science

DOI: 10.1016/j.xfss.2025.10.003