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Related Concept Videos

Microtubule Associated Proteins (MAPs)01:42

Microtubule Associated Proteins (MAPs)

Microtubule function and architecture are regulated by an array of specialized proteins called microtubule-associated proteins or MAPs. These proteins are widespread across different organisms and have conserved protein motifs, like the multi-TOG domain for tubulin binding found in the CLASP family of MAPs. Some MAPs are lineage-specific based on their conserved domains. Their functions depend upon the cytoskeletal architecture and cell type they are located within. In-plant cells, a specific...
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The Spindle Assembly Checkpoint02:19

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Related Experiment Video

Updated: May 11, 2026

Study of the DNA Damage Checkpoint using Xenopus Egg Extracts
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

J Minshull1, H Sun, N K Tonks

  • 1Department of Physiology, University of California, San Francisco 94143-0444.

Cell
|November 4, 1994
PubMed
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.

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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.