(593c) Reorientation During Cell Migration Occurs by a PI3K-Dependent Steering Mechanism

Cell migration requires coordination between intracellular signaling and extracellular cues to orchestrate the cellular processes necessary for efficient cell movement. Further, the spatial heterogeneity and stochasticity of cell signaling events involved in migration require live-cell, spatially-resolved measurements of cell signaling activity along with specialized analytical techniques to determine relationships between dynamic signaling events in a constantly-changing cell. In this work, we use total internal reflection fluorescence (TIRF) microscopy to image membrane-localized signaling events during fibroblast migration and computational techniques to analyze the dynamic localization of these signaling events. Signaling through the phosphoinositide 3-kinase (PI3K) pathway, which occurs primarily in protruding regions of the cell, is thought to affect cell motility, yet its exact roles in random and chemotactic migration remain controversial. By mapping the spatiotemporal dynamics of cell protrusion/retraction, localization of PI3K signaling, and cell morphology during migration, we show that fibroblasts reorient polarity through a PI3K-dependent mechanism involving the branching and pivoting of protrusions. Surprisingly, maximal PI3K signaling occurs just after local protrusion, and inhibition of PI3K signaling does not affect migration speed. During chemotaxis, we find that fibroblasts use this branch-and-pivot steering mechanism to move up a concentration gradient via preferential signaling and protrusion in the branch experiencing the highest concentration of chemoattractant.