Figure 4.

Dynamic Changes in the Localization of Myosin II Drive Convergent Extension and Expansion

(A) Apical wing cross-sections at 4 and 8 hr APF (left). At 4 hr APF Myosin II-GFP is planar polarized along the proximal-distal axis, whereas at 8 hr APF is homogenously distributed (see Figure S3A). Lateral wing cross-sections at 4 hr APF and 8 hr APF (right). From 4 to 8 hr APF, Myosin II-GFP relocates from the apical surface to the lateral membranes (see Figure S3B). Scale bar, 10 μm.

(B) Myosin II-GFP localization in developing Drosophila wings. Maximum projections (left), high-magnification apical-view xy sections (middle), and lateral-view z sections (right) of sqhAX3; {sqh-GFP} wings are shown. Myosin-II is already polarized along the proximal-distal axis at third instar larval wing discs (L3). During convergent extension Myosin-II-GFP (encoded by sqh-GFP, green) accumulates in apical cables, polarized to drive contraction along the anterior-posterior axis. At 6 hr APF, Myosin-II-GFP starts to relocate the lateral side of the cells, and is strongly localized at the lateral domain from 7 to 8 hr APF. Inset at 4 hr APF shows a high-magnification view of the peripodial membrane, which is subsequently removed. Scale bars, 50 μm (left) and 10 μm (middle and right).

(C) Similarly to Myosin-II, Rok-GFP is planar polarized in the imaginal wing disc at late larval stages, but localizes laterally during the expansion phase. Scale bars, 50 μm (left) and 10 μm (middle and right).

(D) Treatment of cultured wings with the Rho-kinase inhibitor Y-27632 for 30 min impairs convergence extension and decreases planar polarization of Myosin-II-GFP in 4 hr 30 min APF wings (see Video S7), and cell flattening and wing extension is impaired in 8 hr 30 min APF wings after 1 hr 30 min treatment. Scale bars, 50 μm (left) and 10 μm (middle and right).

(E) Schematic diagram of wing disc morphogenesis from 4 to 7 hr APF, in apico-basal (top) and sagittal (bottom) cross-sections. Wing blade is shown in yellow and peripodial membrane in gray. Apical and basal ECM are shown in green, and Myosin-II in red. During convergent extension (from 4 hr to 8 hr APF), Myosin-II is localized apically, planar polarized along the anterior-posterior axis to mediate the elongation of the tissue. During expansion, from 6 hr APF, Myosin-II relocalizes to the lateral membrane, concomitant with the isotropic expansion of the wing and the flattening of the columnar epithelia to a cuboidal one.

See also Figures S3 and S4.