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The Spindle Assembly Checkpoint

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The spindle assembly checkpoint is a molecular surveillance mechanism ensuring the fidelity of chromosome segregation during anaphase. The checkpoint monitors the completion of all the prerequisite steps before chromosome segregation to determine whether the segregation process should proceed or be delayed.
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Related Experiment Video

Updated: May 31, 2026

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay

Published on: May 3, 2018

Occludin localizes to centrosomes and modifies mitotic entry.

E Aaron Runkle¹, Jeffrey M Sundstrom², Kristin B Runkle¹

¹Departments of Cellular and Molecular Physiology, Hershey, Pennsylvania 17033.

The Journal of Biological Chemistry

|July 16, 2011

Summary

Occludin, a tight junction protein, is newly found at centrosomes, regulating cell division. Phosphorylation of occludin controls cell cycle progression and epithelial cell homeostasis.

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Area of Science:

Cell Biology
Epithelial Biology
Molecular Biology

Background:

Epithelial cell homeostasis relies on cell cycle control and barrier function.
Tight junction proteins' role in barrier function is known, but their cell cycle roles are emerging.
Centrosomes, crucial for cell division, are linked to cell cycle progression.

Purpose of the Study:

To investigate the novel role of occludin in cell cycle control.
To determine occludin's localization and function at centrosomes.
To explore occludin's impact on centrosome separation and mitosis.

Main Methods:

Immunocytochemistry and biochemical fractionation in Madin-Darby canine kidney cells.
Analysis of occludin phosphorylation at Ser-490.
Stable expression of occludin phosphomimetic (S490D) and nonphosphorylatable (S490A) mutants.

Main Results:

Occludin localizes to centrosomes during interphase.
Occludin phosphorylation at Ser-490 increases during mitosis.
Occludin S490D mutation enhances cell proliferation, while S490A mutation impairs centrosome separation and delays mitotic entry.

Conclusions:

Occludin has a novel function at the centrosome, regulating cell division.
Occludin phosphorylation is critical for proper centrosome separation and mitotic entry.
This study reveals a new mechanism linking tight junction proteins to cell cycle regulation.