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The Contractile Ring and Furrowing in Dividing Cells

The contractile ring is the cytoskeletal structure believed to generate the constriction force for cells that divide by furrowing, namely, all animal cells and a few plant cells. Although its function seems superficially to be reflected in its organization, in many ways it remains poorly understood. To gain an integrated picture of the contractile ring, we need to know a great deal more about what it is morphologically and biochemically, how it works mechanically to produce a furrow, where its components come from and how they are organized, and how its formation is stimulated by antecedent events in mitosis. These are challenging goals, especially in the face of three obstacles: first, the cells that divide by furrowing vary widely in character and the diversity tends to conflict with efforts to find unifying, universal principles of mechanism; second, the techniques for detecting or quantifying the necessary details of the contractile ring are often too crude and imprecise to answer clearly the experimental questions that are asked, and third, the impatience to “solve” the mechanism of furrowing has blurred the distinction between facts and imagination. In this article I will first reiterate the contractile ring’s basic organizational features, for they establish the principle framework in which a morphologist views other aspects of furrowing. I will then briefly consider possible origins of the contractile ring as well as the events that are thought to stimulate its formation. Finally, I will discuss a global contractile phenomenon of the cell cortex that precedes furrowing and that poses a special set of questions concerning furrowing and other allied constriction. I urge any reader who might be seriously interested in furrowing to consult thoroughly the extensive original literature and yet to maintain an open mind about what has been written.