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Cortical flow driven amoeboid migration utilizes friction from retrograde cortical actin flow to generate motion. Many cell types, including cancer cells, can assemble a cortical flow engine to migrate under confinement and low adhesion in vitro, but it remains unclear whether this engine is endogenously utilized in vivo. Moreover, in the context of a changing environment, it is not known how upstream regulation can set in motion and sustain a mutual feedback between flow and polarity. Here, we establish that Drosophila primordial germ cells (PGCs) utilize cortical flow driven amoeboid migration and that flows are oriented by external cues during developmental homing in vivo. The molecular basis of flow modulation is a phosphoregulated feedback loop involving RhoGEF2, a microtubule plus-end tracking RhoA specific RhoGEF, enriched at the rear of PGCs. RhoGEF2 depletion slows and disorganizes cortical flow, reducing migration speed, while RhoGEF2 activation accelerates cortical flow, thereby augmenting myosin II polarity and migration speed. Both perturbations impair PGC pathfinding, suggesting cortical flows must be tuned for accurate guidance. We surprisingly find that RhoGEF2 polarity and activation are independent of upstream canonical Gα12/13 signaling. Instead, its PDZ domain and conserved RhoA binding residues in its PH domain are required to establish a positive feedback loop that augments its basal activity. Upstream regulation of this feedback loop occurs via AMPK dependent multisite phosphorylation near a conserved EB1 binding SxIP motif, which releases RhoGEF2 from EB1 dependent inhibition. Thus, we reveal cortical flows as versatile, tunable engines for directed amoeboid migration in vivo. |
