Spatial Sensing in Fibroblasts Mediated by 3 9 Phosphoinositides ✪ Jason

The directed movement of fibroblasts towards locally released platelet-derived growth factor (PDGF) is a critical event in wound healing. Although recent studies have implicated polarized activation of phosphoinositide (PI) 3-kinase in G protein-mediated chemotaxis, the role of 3 9 PI lipids in tyrosine kinasetriggered chemotaxis is not well understood. Using evanescent wave microscopy and green fluorescent protein–tagged Akt pleckstrin homology domain (GFP– AktPH) as a molecular sensor, we show that application of a shallow PDGF gradient triggers a markedly steeper gradient in 3 9 PI lipids in the adhesion zone of fibroblasts. Polar GFP–AktPH gradients, as well as a new type of radial gradient, were measured from front to rear and from the periphery to the center of the adhesion zone, respectively. A strong spatial correlation between polarized 3 9 PI production and rapid membrane spreading implicates 3 9 PI lipids as a direct mediator of polarized migration. Analysis of the temporal changes of 3 9 PI gradients in the adhesion zone revealed a fast diffusion coefficient (0.5 m m 2 /s) and short lifetime of 3 9 PIs of , 1 min. Together, this study suggests that the tyrosine kinase-coupled directional movement of fibroblasts and their radial membrane activity are controlled by local generation and rapid degradation of 3 9 PI second messengers.