FIGURE 2.

Cytoskeleton polarity during notochord development in Ciona. (A) F-actin accumulates at the lamellipodium tip, providing migrating forces for cell intercalation. (B) Ventrally accumulated actomyosin contractility provides unbalanced force to drive notochord bending. (C) An actomyosin contractile ring forms at the anterior edge and moves to the equator of notochord cells. Actomyosin ring contraction elongates notochord cells. Microtubules are perpendicular to the AP axis within notochord cells. (D) During lumen expansion, microtubules accumulate at the apical domain, and along with bidirectional migration, they rotate 90° and form oriented bundles toward the leading edges of tractive lamellipodia-like protrusions. An actomyosin contractile ring also exists during lumen expansion and then disappears. At bidirectional migration, F-actin moves to the tip of lamellipodia-like protrusions.