THREE-DIMENSIONAL CELL INTERCALATION DRIVES DROSOPHILA GERMBAND EXTENSION

Abstract

Drosophila germband extension (GBE) depends on directed cell intercalation, which is driven by myosin II-mediated contraction at adherens junction on cell’s apical side. Here I characterized how cells coordinate their shape and movement in three-dimensions during rosette formation - a hallmark of cell intercalation - and show that that basolateral rosette formation is driven by cells locate at the dorsal/ventral part of the cell cluster (D/V cells). D/V cells exhibit wedge-shaped basolateral protrusions and migrate towards each other along the converging D/V axis. Surprisingly, the formation of basolateral rosette precedes that of apical rosette and is independent of apical contractility. Rather, it requires Rac1-dependent cell motility. Src42A is a basal-specific regulator during intercalation. Reduction of Src42A leads to abnormal basal intercalation but retains apical rosette formation, which eventually results in delayed GBE. This study shows that cell crawling via basolateral protrusions plays a pivotal role in cell intercalation and GBE.