PARTICLES MOVE ALONG ACTIN FILAMENT BUNDLES IN NERVE GROWTH CONES

Organelle movement along actin filaments has been demonstrated in diss ociated squid axoplasm [Kurznetsov, S.A., Langford, G.M. & Weiss, D.G. (1992) Nature (London) 356, 722-725 and Bearer, E.L., DeGiorgis, J.A. , Bodner, R.A., Rao, A.W. & Reese, T.S. (1993) Proc. Natl. Acad. Sci. USA 90, 11252-11256] but has not been shown to occur in intact neurons , Here we demonstrate that intracellular transport occurs along actin filament bundles in intact neuronal growth cones. We used video-enhanc ed differential interference contrast microscopy to observe intracellu lar transport in superior cervical ganglion neurons cultured under con ditions that enhance the visibility of actin bundles within growth con e lamellipodia. Intracellular particles, ranging in size from <0.5-1.5 mu m, moved along linear structures (termed transport bundles) at an average maximum rate of 0.48 mu m/sec. After particle movement had bee n viewed, cultures were preserved by rapid perfusion with chemical fix ative, To determine whether particle transport occurred along actin, w e then used fluorescence microscopy to correlate this movement with ac tin and microtubule distributions in the same growth cones, The observ ed transport bundles colocalized with actin but not with microtubules. The rates of particle movement and the association of moving particle s with actin filament bundles suggest that myosins may participate in the transport of organelles (or other materials) in intact neurons.