A gradient of 3′ phosphoinositide (PI) lipids, oriented towards a chemoattractant source, is generated by G protein-coupled receptors in both Dictyostelium and neutrophils. On page 1269, Haugh et al. show that a similar polar gradient is generated in fibroblasts in response to platelet-derived growth factor (PDGF) stimulation of a tyrosine kinase receptor.
But Haugh et al. do not stop there. They use sophisticated microscopy to focus only on the base of the cell, where they observe another gradient. This second, radial gradient of PI lipids increases from the center to the periphery of the cell. Haugh et al. propose that cells generate certain PI lipids only on their free, nonadherent surfaces, and that these lipids then diffuse, as they are being degraded, to the adherent surface. The resultant radial gradient may help define a peripheral zone in which...
