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Cell cycle checkpoints: arresting progress in mitosis
1Dept of Cell Biology, University of Virginia Health Sciences Center, Charlottesville 22908, USA. GJG5y@virginia.edu
Abstract:
Cell cycle arrest in M phase can be induced by the failure of a single chromosome to attach properly to the mitotic spindle. The same cell cycle checkpoint mediates M phase arrest when cells are treated with drugs that either disrupt or hyperstabilize spindle microtubules. Study of yeast mutants that fail to arrest in the presence of microtubule disruptors identified a set of genes important in this checkpoint pathway. Two recent papers report the cloning of human and Xenopus homologues of one of these yeast genes, called MAD2 (for mitotic arrest deficient-2)(1,2). Introduction of antibodies to the MAD2 protein into living mammalian cells or Xenopus egg extracts abrogates the M phase arrest induced by microtubule inhibitors. This and other recent developments suggest a model for the M phase checkpoint in which unattached kinetochores inhibit the ubiquitination of proteins whose proteolysis is necessary for chromatid separation and exit from mitosis.
Insights
Proper chromosome attachment to the mitotic spindle is crucial for cell division. The MAD2 gene plays a key role in the M phase checkpoint, ensuring correct cell cycle progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Cell cycle arrest at M phase is triggered by improper chromosome attachment to the mitotic spindle.
- This arrest is mediated by a checkpoint that responds to disruptions or hyperstabilization of spindle microtubules.
- Yeast mutants lacking this checkpoint identified key genes, including MAD2.
Purpose of the Study:
- To investigate the role of the MAD2 gene in the M phase cell cycle checkpoint.
- To understand the mechanism by which MAD2 influences cell cycle progression and chromosome segregation.
Main Methods:
- Studied yeast mutants defective in the M phase checkpoint.
- Cloned human and Xenopus homologues of the yeast MAD2 gene.
- Utilized antibodies against the MAD2 protein in mammalian cells and Xenopus egg extracts.
Main Results:
- Identified MAD2 as a critical gene in the M phase checkpoint pathway.
- Demonstrated that MAD2 homologues exist in higher eukaryotes (human and Xenopus).
- Showed that anti-MAD2 antibodies block M phase arrest induced by microtubule inhibitors.
Conclusions:
- Unattached kinetochores likely inhibit protein ubiquitination, preventing chromatid separation and mitotic exit.
- MAD2 is a conserved component of the M phase checkpoint essential for accurate cell division.
- This research provides insights into the molecular mechanisms governing cell cycle regulation and error correction.