Cytokinesis contractile ring

Emoto, K., and Umeda, M., 2000, An essential role for a membrane phosphohpid in cytokinesis Regulation of contractile ring disassembly by redistribution of phosphatidylethanolamine. J. Cell Biol., 149 1215-1224. 

Cytokinesis begins some time in anaphase. A cleavage furrow begins to form in the plasma membrane in the same plane as the metaphase plate. It is not known how the furrow is positioned. The furrow is created and deepens due to the actions of the contractile ring which is an actomyosin network assembled specifically for this purpose and dispersed afterward. Thus, the stability of this network is quite different from its analog in muscle. The dynamics of these networks are also different (see Prob. 5.16). 

The final mitosis stage involves separation of two sets of chromosomes via microtubules that are filamentous polymers of tubulin monomers. Compounds that interfere with tubulin polymerization such as the plant-derived compounds colchicine, taxol, vinblastine and vincristine are cell division inhibitors (Table 9.6). The cytokinesis of the daughter cells requires equal division of cytoplasm and an actin-myosin-based contractile ring provides the force to make this separation. Accordingly, compounds such as cytochalasin B that interfere with actin will also interfere with cell division (Table 9.6). 

Membrane traffic a driving force in cytokinesis, Trends Cell Biol. 15, 92-101, 2005 Glotzer, M., The molecular requirements for cytokinesis. Science 307, 1735-1739, 2005 Burgess, D.R., Cytokinesis new roles for myosin, Curr. Biol. 15, R310-R311, 2005 Darenfeld, H. and Mandato, C.A., Wound-induced contractile ring a model for cytokinesis, Biochem. Cell Biol. 83, 711-720, 2005 Konopka, C.A., Scheede, J.B., Skop, A.R., and Bednarek, S.Y., Dynamin and cytokinesis. Traffic 7, 239-247, 2006. 

Figure 5 Force production by the contractile ring in cytokinesis, (a) A ring of actin filaments forms at the plasma membrane and contracts to divide the cell in half, (b) Structure of cytochalasin B, a small molecule that targets actin.

The results of experiments In which active myosin II is eliminated from the cell demonstrate that cytokinesis is indeed dependent on myosin II (Figure 19-21). In one type of experiment, antl-myosin II antibodies are microinjected into one cell of a sea urchin embryo at the two-cell stage. In other experiments, expression of myosin II Is Inhibited by deletion of the myosin gene or by antisense Inhibition of myosin mRNA expression. In all cases, a cell lacking myosin II replicates to form a multinucleated syncytium because cytokinesis, but not chromosome separation, Is Inhibited. Without myosin II, cells fail to assemble a contractile ring, although other events in the cell cycle proceed normally. 

The contractile ring, a transient bundle of actin and myosin II, forms In a dividing cell and pinches the cell Into two halves In cytokinesis. 

During cytokinesis, the final step in cell division, the actin and myosin filaments composing the contractile ring slide past each other to form a cleavage furrow of steadily decreasing... 

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