GAP-43 mRNA in growth cones is associated with HuD and ribosomes

The neuron-specific ELAV/Hu family member, HuD, interacts with and stabilizes GAP-43 mRNA in developing neurons, and leads to increased levels of GAP-43 protein. As GAP-43 protein is enriched in growth cones, it is of interest to determine if HuD and GAP-43 mRNA are associated in developing growth cones. HuD granules in growth cones are found in the central domain that is rich in microtubules and ribosomes, in the peripheral domain with its actin network, and in filopodia. This distribution of HuD granules in growth cones is dependent on actin filaments but not on microtubules. GAP-43 mRNA is localized in granules found in both the central and peripheral domains, bat not in filopodia. Ribosomes were extensively colocalized with HuD and GAP-43 mRNA granules in the central domain, consistent with a role in the control of GAP-43 mMNA stability in the growth cone. Together, these results demonstrate that many of the components necessary for GAP-43 mRNA translation/stabilization are present within growth cones.