Axonal elongation triggered by stimulus-induced local translation of a polarity complex protein.

During development, axon growth rates are precisely regulated to provide temporal control over pathfinding. The precise temporal regulation of axonal growth is a key step in the formation of functional synapses and the proper patterning of the nervous system. The rate of axonal elongation is increased by factors such as netrin-1 and nerve growth factor (NGF), which stimulate axon outgrowth using incompletely defined pathways. To clarify the mechanism of netrin-1- and NGF-stimulated axon growth, we explored the role of local protein translation. We found that intra-axonal protein translation is required for stimulated, but not basal, axon outgrowth. To identify the mechanism of translation-dependent outgrowth, we examined the PAR complex, a cytoskeleton regulator. We found that the PAR complex, like local translation, is required for stimulated, but not basal, outgrowth. Par3 mRNA is localized to developing axons, and NGF and netrin-1 trigger its local translation. Selective ablation of Par3 mRNA from axons abolishes the outgrowth-promoting effect of NGF. These results identify a new role for local translation and the PAR complex in axonal outgrowth.