Regulation of NGF Signaling by an Axonal Untranslated mRNA.

Neurons are extraordinarily large and highly polarized cells that require rapid and efficient communication between cell bodies and axons over long distances. In peripheral neurons, transcripts are transported along axons to growth cones, where they are rapidly translated in response to extrinsic signals. While studying Tp53inp2, a transcript highly expressed and enriched in sympathetic neuron axons, we unexpectedly discovered that Tp53inp2 is not translated. Instead, the transcript supports axon growth in a coding-independent manner. Increasing evidence indicates that mRNAs may function independently of their coding capacity; for example, acting as a scaffold for functionally related proteins. The Tp53inp2 transcript interacts with the nerve growth factor (NGF) receptor TrkA, regulating TrkA endocytosis and signaling. Deletion of Tp53inp2 inhibits axon growth in vivo, and the defects are rescued by a non-translatable form of the transcript. Tp53inp2 is an atypical mRNA that regulates axon growth by enhancing NGF-TrkA signaling in a translation-independent manner.