Mechanics of cytokinesis in eukaryotes

Abstract

Research on eukaryotic cytokinesis using advantageous model systems is rapidly advancing our understanding of most aspects of the process. Cytokinesis is very complicated with more than 100 proteins participating. Both fungi and animal cells use proteins to mark the cleavage site for the assembly of a contractile ring of actin filaments and myosin-II. Formins nucleate and elongate the actin filaments and myosin-II helps to organize the filaments into a contractile ring. Much is still to be learned about the organization of the contractile ring and the mechanisms that disassemble the ring as it constricts. Although fungi and animals share many proteins that contribute to cytokinesis, the extent to which they share mechanisms for the location, assembly, constriction, and disassembly of their contractile rings is still in question.

Figure 1

Drawing of contractile ring assembly and constriction in three model organisms. (a) Fission yeast. (b) Budding yeast. (c) Animal cells.

Figure 2

Simple drawings of the organization of contractile rings. The example shown is from animal cells but the arrangement of antiparallel actin filaments and interactions with myosin-II are thought to apply to fungi and amebas as well. Attachment of the barbed ends of the actin filaments to the plasma membrane via a formin is hypothetical. As myosin-II walks toward the barbed end of an associated actin filament it will apply tension to the plasma membrane. Illustrations by Graham Johnson.