Fig. 7. A myosin IIB-dependent cortical actin network functions to integrate cell adhesion and polarization to generate directed forces driving morphogenesis. (A) Cell intercalation in the Xenopus notochord requires two distinct cell activities: cell contraction in the cell body (gray arrows) and polarized protrusive activity (black arrows). (B) Contraction events are driven by the myosin IIB-dependent cortical actin network (green lines), which is organized into dynamic foci (black) and interacts with myosin IIB at adhesion sites (red). (C) Integrating this episodic cell shortening with polarized protrusive activity and dynamically regulated myosin IIB-dependent adhesion leads to cell intercalation (white arrows) and tissue-level convergence and extension (large black arrows). The deeply interdigitated notochordal cells at this stage have adopted a monopolar protrusive activity (small black arrows). The extracellular matrix of the NSB is lateral in each case.