FIGURE 5:

Model for the actin cytoskeleton structure in C. elegans zygotes. (A) Schematic of the hypothesized structure of the actin cytoskeleton that drives rotation in adherent mammalian cells (adapted from Tee et al., 2015). Peripheral, anchored formins (blue) generate radial F-actin (orange) under torque (red) and coupled to circumferential bundles (yellow) whose contractility leads to a counterclockwise skew (purple). (B) Cut-away perspective view into the posterior pole of the C. elegans zygote illustrating hypothetical mechanism for cortical rotation: Membrane-anchored, posterior-enriched formins (blue) generate longitudinal (posterior-to-anterior) bundles that interact with circumferential cytokinetic ring actin bundles (yellow). Contraction in the ring could relieve chiral torque (red) within posterior-to-anterior bundles (orange), generating a right-handed rotation (purple). Septins (green) could contribute to this phenomenon by localizing/anchoring formins to the posterior cortex or cross-linking within or between actin bundle populations.