Cdc42 stimulates neurite outgrowth and formation of growth cone filopodia and lamellipodia

To assess the role of cdc42 during neurite development, cmyc-tagged constit utively active (CA) and dominant negative (DN) cdc42 were expressed in diss ociated primary chick spinal cord neurons using adenoviral-mediated gene tr ansfer. Three days after infection, >85% of the neurons in infected culture s expressed cdc42 proteins, as detected by indirect immunofluorescence agai nst cmyc. Growth cones of infected neurons displayed 1.83- (CAcdc42) and 1. 93-fold (DNcdc42) higher cmyc immunofluorescence per square micrometer than uninfected controls. CAcdc42 expression stimulated growth cones, almost do ubling growth cone size and number of filopodia, and increased neurite grow th rates by 65-89%. In neurons plated onto fibronectin, the percent of grow th cones with both filopodia and lamellipodia increased from 71 to 92%. Tot al Texas Red-phalloidin staining in these growth cones doubled, and the per cent of growth cones with F-actin localized to peripheral regions increased from 52% in controls to 78% after CAcdc42 expression. Expression of DNcdc4 2 did not significantly alter growth cone morphology or neurite growth rate s. Addition of soluble laminin to spinal cord neurons resulted in the ident ical phenotype as CAcdc42 expression, including changes in growth cone morp hology, F-actin localization, and neurite growth rates. Significantly, expr ession of DNcdc42 blocked the effects of laminin on growth cones. These res ults show that cdc42 promotes neurite outgrowth and filopodial and lamellip odial formation in growth cones and suggests that cdc42 and laminin share a common signaling pathway during neurite development. Addition of laminin t o CAcdc42 expressing neurons is inhibitory to growth cones, indicating that laminin also may activate some other pathways. (C) 2000 John Wiley & Sons, Inc.