We observed live fission yeast expressing pairs of functional fluorescent fusion proteins to test the popular model that the cytokinetic contractile ring assembles from a single myosin II progenitor or a Cdc12p-Cdc15p spot. Under our conditions, the anillin-like protein Mid1p establishes a broad band of small dots or nodes in the cortex near the nucleus. These nodes mature by the addition of conventional myosin II (Myo2p, Cdc4p, and Rlc1p), IQGAP (Rng2p), pombe Cdc15 homology protein (Cdc15p), and formin (Cdc12p). The nodes coalesce laterally into a compact ring when Cdc12p and profilin Cdc3p stimulate actin polymerization. We did not observe assembly of contractile rings by extension of a leading cable from a single spot or progenitor. Arp2/3 complex and its activators accumulate in patches near the contractile ring early in anaphase B, but are not concentrated in the contractile ring and are not required for assembly of the contractile ring. Their absence delays late steps in cytokinesis, including septum formation and cell separation.
Assembly of the cytokinetic contractile ring from a broad band of nodes in fission yeast
D.R. Kovar's present address is Depts. of Molecular Genetics and Cell Biology and Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637.
M. Lord's present address is Dept. of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405.
Abbreviations used in this paper: Arp2/3, actin-related protein 2/3; DIC, differential interference contrast; Lat-A, latrunculin A; mCFP, monomeric CFP; mYFP, monomeric YFP; PCH, pombe Cdc15 homology; SPB, spindle pole body; WASp, Wiskott-Aldrich syndrome protein.
Jian-Qiu Wu, Vladimir Sirotkin, David R. Kovar, Matthew Lord, Christopher C. Beltzner, Jeffrey R. Kuhn, Thomas D. Pollard; Assembly of the cytokinetic contractile ring from a broad band of nodes in fission yeast . J Cell Biol 31 July 2006; 174 (3): 391–402. doi: https://doi.org/10.1083/jcb.200602032
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