Association of Spindle Assembly Checkpoint Component XMAD2 with Unattached Kinetochores

TLDR

The spindle assembly checkpoint postpones anaphase until all chromosomes are properly attached to the spindle, a function lost in mad and bub mutants that fail to arrest when microtubules are depolymerized. This study aims to deepen understanding of cell cycle checkpoint mechanisms in metazoa and to provide a marker for investigating spindle checkpoint roles in tumor genomic instability. A frog homolog of MAD2, XMAD2, was isolated and shown to associate with unattached kinetochores during prometaphase and nocodazole treatment, disappearing at metaphase, indicating its essential role in checkpoint activation by unattached kinetochores.

Abstract

The spindle assembly checkpoint delays anaphase until all chromosomes are attached to a mitotic spindle. The mad (mitotic arrest-deficient) and bub (budding uninhibited by benzimidazole) mutants of budding yeast lack this checkpoint and fail to arrest the cell cycle when microtubules are depolymerized. A frog homolog of MAD2 ( XMAD2 ) was isolated and found to play an essential role in the spindle assembly checkpoint in frog egg extracts. XMAD2 protein associated with unattached kinetochores in prometaphase and in nocodazole-treated cells and disappeared from kinetochores at metaphase in untreated cells, suggesting that XMAD2 plays a role in the activation of the checkpoint by unattached kinetochores. This study furthers understanding of the mechanism of cell cycle checkpoints in metazoa and provides a marker for studying the role of the spindle assembly checkpoint in the genetic instability of tumors.