GROWTH CONE COLLAPSE AND INHIBITION OF NEURITE GROWTH BY BOTULINUM NEUROTOXIN C1 - A T-SNARE IS INVOLVED IN AXONAL GROWTH

The growth cone is responsible for axonal growth, where membrane expan sion is most likely to occur. Several recent reports have suggested th at presynaptic proteins are involved in this process; however, the mol ecular mechanism details are unclear, We suggest that by cleaving a pr esynaptic protein syntaxin, which is essential in targeting synaptic v esicles as a target SNAP receptor (t-SNARE), neurotoxin C1 of Clostrid ium botulinum causes growth cone collapse and inhibits axonal growth. Video-enhanced microscopic studies showed (a) that neurotoxin C1 selec tively blocked the activity of the central domain (the vesicle-rich re gion) at the initial stage, but not the lamellipodia in the growth con e; and (b) that large vacuole formation occurred probably through the fusion of smaller vesicles from the central domain to the most distal segments of the neurite, The total surface area of the accumulated vac uoles could explain the membrane expansion of normal neurite growth. T he gradual disappearance of the surface labeling by FITC-WGA on the no rmal growth cone, suggesting membrane addition, was inhibited by neuro toxin C1, The experiments using the peptides derived from syntaxin, es sential for interaction with VAMP or alpha-SNAP, supported the results using neurotoxin C1. Our results demonstrate that syntaxin is involve d in axonal growth and indicate that syntaxin may participate directly in the membrane expansion that occurs in the central domain of the gr owth cone, probably through association with VAMP and SNAPs, in a SNAR E-like way.