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Updated: May 11, 2026
10:55
Study of the DNA Damage Checkpoint using Xenopus Egg Extracts
Published on: November 5, 2012
A MAP kinase-dependent spindle assembly checkpoint in Xenopus egg extracts
1Department of Physiology, University of California, San Francisco 94143-0444.
Cell
|November 4, 1994
Summary
Xenopus egg extracts normally lack cell cycle checkpoints. However, high sperm concentrations induce mitotic arrest by depolymerizing microtubules, requiring mitogen-activated protein (MAP) kinase activity.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Early Xenopus embryos and egg extracts typically lack the anaphase-promoting complex/cyclosome (APC/C) checkpoint.
- This checkpoint normally prevents entry into anaphase until spindle assembly is complete.
Purpose of the Study:
- To investigate the mechanisms of mitotic arrest in Xenopus egg extracts under specific conditions.
- To determine the role of mitogen-activated protein (MAP) kinase in regulating the cell cycle in these extracts.
Main Methods:
- Utilizing Xenopus egg extracts with high densities of sperm nuclei to induce microtubule depolymerization.
- Assessing mitotic arrest by measuring maturation-promoting factor (MPF) activity, cyclin B degradation, and ERK2/MAP kinase activation.
- Employing the MAP kinase-specific phosphatase MKP-1 to probe the necessity of MAP kinase activity.
Main Results:
- High sperm densities caused microtubule depolymerization, arresting extracts in mitosis.
- Arrested extracts exhibited high MPF activity, failed cyclin B degradation, and showed activated ERK2/MAP kinase.
- Addition of MKP-1 reversed the mitotic arrest, indicating MAP kinase is essential for its establishment and maintenance.
Conclusions:
- Mitotic arrest in Xenopus egg extracts can be induced by spindle depolymerization at high sperm densities.
- Activated MAP kinase signaling is crucial for both initiating and sustaining this specific mitotic arrest.
- Calcium, which typically releases meiotic arrest, does not affect this spindle depolymerization-induced mitotic arrest.
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