Molecular Biology of the Cell Vol. 28, No. 5 Article

Despite recent advances in our understanding of the components and spatial regulation of the contractile ring (CR), the precise ultrastructure of actin and myosin II within the animal cell CR remains an unanswered question. 

The combined efforts of many investigators have led to a near-complete parts list for the CR and a consensus on how the cleavage plane is specified (reviewed in Eggert et al., 2006; Green et al., 2012). However, achieving a mechanistic understanding of how the ring assembles and constricts in animal cells requires that the precise arrangement of contractile proteins be determined.

our results provide clear structural evidence for a sliding filament–based mechanism of cell division in sea urchin embryos and that this finding may be applicable to cytokinesis in a wide variety of other cell types.