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Vol. 17, Issue 9, 4093-4104, September 2006

This Article Full Text Full Text (PDF) Supplemental Material All Versions of this Article: E06-02-0119v1 17/9/4093    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lucero, A. Articles by Shuster, C. B. Search for Related Content PubMed PubMed Citation Articles by Lucero, A. Articles by Shuster, C. B.

A Global, Myosin Light Chain Kinase-dependent Increase in Myosin II Contractility Accompanies the Metaphase–Anaphase Transition in Sea Urchin Eggs

Amy Lucero^*, Christianna Stack^*, Anne R. Bresnick, and Charles B. Shuster^*,

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

Submitted February 9, 2006; Revised June 15, 2006; Accepted July 5, 2006
Monitoring Editor: Yu-li Wang

Myosin II is the force-generating motor for cytokinesis, and although 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. Last, 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 myosin light chain kinase (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.

This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E06-02-0119) on July 12, 2006.

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

Abbreviations used: CaFSW, calcium-free seawater; IP₃, inositol-1,4,5-triphosphate; MLCK, myosin light chain kinase; MRLC, myosin regulatory light chain; NEB, nuclear envelope breakdown; ROCK, Rho-kinase

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