Ability to divide is one of the basic properties of a cell. In metazoans, where cells divide in a context of germ layers, tissues, and organs, cell proliferation must be coordinated with differentiation to prevent developmental abnormalities. Genetic analyses in simple model systems (yeast, slime mold, fruit fly) have demonstrated that defects in either karyokinesis, or nuclear division (e.g., mutations that affect cell cycle checkpoints, mitotic chromosome condensation and segregation, etc.), or cytokinesis (Fig. 1), both may delay or block development.
Early studies of cytokinesis in animal cells took advantage of the ability to easily manipulate and observe large transparent eggs of marine invertebrates, such as echinoderms and ctenophores (reviewed by Rappaport 1996). These simple but informative micromanipulation experiments have demonstrated that an actomyosin contractile ring is the driving force of cytokinesis and have led to...
