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MBC in Press, published online ahead of print July 12, 2006
Mol. Biol. Cell 10.1091/mbc.E06-02-0119

A more recent version of this article appeared on September 1, 2006
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Submitted on February 9, 2006
Revised on June 15, 2006
Accepted on July 5, 2006

A Global, MLCK-dependent Increase in Myosin II Contractility Accompanies the Metaphase-Anaphase Transition in Sea Urchin Eggs

Amy Lucero,* Christianna Stack,* Anne R. Bresnick,{dagger} and Charles B. Shuster*{ddagger}

*Department of Biology, New Mexico State University, Las Cruces, NM 88003; {dagger}Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461; {ddagger}Marine Biological Laboratory, Woods Hole, MA 02543

Monitoring Editor: Yu-li Wang

Myosin II is the force-generating motor for cytokinesis, and while it is accepted that myosin contractility is greatest at the cell equator, the temporal and spatial cues that direct equatorial contractility are not known. Dividing sea urchin eggs were placed under compression to study myosin II-based contractile dynamics, and cells manipulated in this manner underwent an abrupt, global increase in cortical contractility concomitant with the metaphase-anaphase transition, followed by a brief relaxation and the onset of furrowing. Prefurrow cortical contractility both preceded and was independent of astral microtubule elongation, suggesting that the initial activation of myosin II preceded cleavage plane specification. The initial rise in contractility required myosin light chain kinase but not Rho-kinase, but both signaling pathways were required for successful cytokinesis. Lastly, mobilization of intracellular calcium during metaphase induced a contractile response, suggesting that calcium transients may be partially responsible for the timing of this initial contractile event. Together, these findings suggest that myosin II-based contractility is initiated at the metaphase-anaphase transition by Ca2+-dependent MLCK activity, and is maintained through cytokinesis by both MLCK- and Rho-dependent signaling. Moreover, the signals that initiate myosin II contractility respond to specific cell cycle transitions independently of the microtubule-dependent cleavage stimulus.

Address correspondence to: Charles B. Shuster (cshuster{at}nmsu.edu)




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M. Zhou and Y.-L. Wang
Distinct Pathways for the Early Recruitment of Myosin II and Actin to the Cytokinetic Furrow
Mol. Biol. Cell, January 1, 2008; 19(1): 318 - 326.
[Abstract] [Full Text] [PDF]


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