Phospholipase D2 acts upstream of PI4P 5-kinases in the response of neurons to extracellular viscosity

The formation of an axon during neuronal differentiation is determined by the competition of positive and negative signals that promote and inhibit extension, respectively. Several biochemical signals have been identified that promote axon extension, but it is just beginning to be appreciated that the physical properties of the extracellular environment also play an important role. Using primary cultures, we show that developing central neurons respond to an increase in extracellular viscosity. This response depends on plasma membrane glycolipids and Phospholipase D2 (Pld2). Pld2 acts upstream of type 1 phosphatidylinositol 4-phosphate 5-kinases (Pip5ks) to regulate the generation of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P 2 ) as an inhibitory signal for axon extension. The glucosylceramide GM1 that negatively regulates Pld2 is increased in neurites by a shift to high viscosity. Our results suggest that changes in the physical properties of the extracellular environment regulate axon extension by modulating plasma membrane glycolipids and Pld2/Pip5k1 signaling.