The Axonal Transcriptome: RNA Localization and Function

Neurons are highly polarized cells, often with very long processes, which can comprise up to 95% of the cytoplasm. This raises the issue of transporting and turnover of proteins transport. In addition to fast axonal transport, axonal translation has been proposed to be responsible for producing at least some axonal proteins. In multiple experimental models, local synthesis of several proteins has been demonstrated in axons, growth cones, and nerve terminals. Multiple lines of evidence are consistent with the existence of axonal rRNAs, mRNAs, tRNAs, and micro RNAs and micro RNA regulatory proteins (RISC complex). Multiple signalling pathways, including mTOR, may regulate axonal translation. The origin of axonal RNAs is often attributed to transport from the neuronal soma, but evidence supporting cell-to-cell transport from Schwann cells to axons as a source of at least some axonal RNAs is emerging. This intercellular transport will be discussed in the context of normal and regenerative conditions.