Repeat-element RNAs integrate a neuronal growth circuit.

Neuronal growth and regeneration are regulated by local translation of mRNAs in axons. We examined RNA polyadenylation changes upon sensory neuron injury and found upregulation of a subset of polyadenylated B2-SINE repeat elements, hereby termed GI-SINEs (growth-inducing B2-SINEs). GI-SINEs are induced from ATF3 and other AP-1 promoter-associated extragenic loci in injured sensory neurons but are not upregulated in lesioned retinal ganglion neurons. Exogenous GI-SINE expression elicited axonal growth in injured sensory, retinal, and corticospinal tract neurons. GI-SINEs interact with ribosomal proteins and nucleolin, an axon-growth-regulating RNA-binding protein, to regulate translation in neuronal cytoplasm. Finally, antisense oligos against GI-SINEs perturb sensory neuron outgrowth and nucleolin-ribosome interactions. Thus, a specific subfamily of transposable elements is integral to a physiological circuit linking AP-1 transcription with localized RNA translation.