Local Translation of Transport-Machinery mRNAs in Axons

Localized translation enables rapid and efficient response to local needs and is especially important in polarized cells. Neurons are highly polarized cells and have been shown to exploit localized translation to regulate protein synthesis at distal compartments, including axons and synapses. Localized translation of transport-machinery mRNA to fuel axonal transport offer an efficient mechanism to maintain proper transport, but was not studied yet. In this study we show that mRNA of many transport machinery proteins, including Kinesin family (Kif) members and Trak proteins (kinesin-cargo adaptors) are enriched in neuronal axons compared to the soma. Live imaging of cells transfected with different segments of Trak1 and Trak2 3` UTRs reveal variable levels of axonal localization, indicating that mRNA localization to the axon is, at least partially, dictated by 3` UTR elements. The different 3` UTR segments were expressed using the same promotor, yet detected at different levels, suggesting the presence of stabilizing/destabilizing element on these segments. An RNA decay assay revealed higher stability of endogenous Trak mRNA in axons compared to soma. Thus, localization of mRNA encoding transport machinery proteins to axons is mediated by 3` UTR elements, and might be dictated not only by an active mRNA transport, but also by mRNA stability regulation.