Live imaging of late-stage preimplantation human embryos reveals de novo mitotic errors.

De novo mitotic errors, including multipolar spindles and lagging chromosomes, occur frequently in late-stage preimplantation human embryos, with most lagging chromosomes passively inherited.

• Why it matters: Understanding when and how chromosomal missegregation occurs in human embryos is crucial, as such errors are a leading cause of miscarriage and infertility, yet their timing postfertilization remains unclear.
• What they did: The study used optimized nuclear DNA labeling via messenger RNA electroporation and light-sheet live imaging, along with a deep learning-based segmentation method, to observe chromosome segregation errors in advanced preimplantation stages.
• The result: Findings suggest that chromosomal errors are common before implantation, raising questions about the reliability of preimplantation genetic testing, and provide new imaging tools for studying human embryonic development.