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Vol. 20, Issue 24, 5195-5210, December 15, 2009

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Roles of Formin Nodes and Myosin Motor Activity in Mid1p-dependent Contractile-Ring Assembly during Fission Yeast Cytokinesis

Valerie C. Coffman^*, Aaron H. Nile^*,, I-Ju Lee^*,, Huayang Liu^*, and Jian-Qiu Wu^*,

*Department of Molecular Genetics, Graduate Program of Molecular, Cellular, and Developmental Biology, and Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, OH 43210

Submitted May 28, 2009; Revised September 21, 2009; Accepted October 15, 2009
Monitoring Editor: Daniel J. Lew

InCytes from MBC

Two prevailing models have emerged to explain the mechanism of contractile-ring assembly during cytokinesis in the fission yeast Schizosaccharomyces pombe: the spot/leading cable model and the search, capture, pull, and release (SCPR) model. We tested some of the basic assumptions of the two models. Monte Carlo simulations of the SCPR model require that the formin Cdc12p is present in >30 nodes from which actin filaments are nucleated and captured by myosin-II in neighboring nodes. The force produced by myosin motors pulls the nodes together to form a compact contractile ring. Live microscopy of cells expressing Cdc12p fluorescent fusion proteins shows for the first time that Cdc12p localizes to a broad band of 30–50 dynamic nodes, where actin filaments are nucleated in random directions. The proposed progenitor spot, essential for the spot/leading cable model, usually disappears without nucleating actin filaments. -Actinin ain1 deletion cells form a normal contractile ring through nodes in the absence of the spot. Myosin motor activity is required to condense the nodes into a contractile ring, based on slower or absent node condensation in myo2-E1 and UCS rng3-65 mutants. Taken together, these data provide strong support for the SCPR model of contractile-ring formation in cytokinesis.

Present address: Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599.

Address correspondence to: Jian-Qiu Wu (wu.620{at}osu.edu).

Abbreviations used: CHD, calponin homology domain; fps, frames per second; FRAP, fluorescence recovery after photobleaching; Lat-A, latrunculin A; MT, microtubule; PCH, pombe Cdc15 homology; ROI, region of interest; SCPR, search, capture, pull, and release; SPB, spindle pole body.

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