Spindle assembly checkpoint insensitivity allows meiosis-II despite chromosomal defects in aged eggs.

Document Type

Article

Publication Date

11-6-2023

Keywords

JMG, Female, Animals, Spindle Apparatus, M Phase Cell Cycle Checkpoints, Meiosis, Oocytes, Chromatids, Aneuploidy, Chromosome Segregation, Mammals

JAX Source

EMBO Rep. 2023;24(11):e57227.

ISSN

1469-3178

PMID

37795949

DOI

https://doi.org/10.15252/embr.202357227

Grant

This research was supported by the grants to GF from Canadian Institute for Health Research (CIHR) and Foundation Jean-Louis Levesque. AIM was supported by the Fonds de Recherche du Quebec- Sante (FRQS) and McGill’s Centre for Research in Reproduction and Development (CRRD) Postdoctoral Fellowships.

Abstract

Chromosome segregation errors in mammalian oocyte meiosis lead to developmentally compromised aneuploid embryos and become more common with advancing maternal age. Known contributors include age-related chromosome cohesion loss and spindle assembly checkpoint (SAC) fallibility in meiosis-I. But how effective the SAC is in meiosis-II and how this might contribute to age-related aneuploidy is unknown. Here, we developed genetic and pharmacological approaches to directly address the function of the SAC in meiosis-II. We show that the SAC is insensitive in meiosis-II oocytes and that as a result misaligned chromosomes are randomly segregated. Whilst SAC ineffectiveness in meiosis-II is not age-related, it becomes most prejudicial in oocytes from older females because chromosomes that prematurely separate by age-related cohesion loss become misaligned in meiosis-II. We show that in the absence of a robust SAC in meiosis-II these age-related misaligned chromatids are missegregated and lead to aneuploidy. Our data demonstrate that the SAC fails to prevent cell division in the presence of misaligned chromosomes in oocyte meiosis-II, which explains how age-related cohesion loss can give rise to aneuploid embryos.

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