The RNA Binding proteome of axonal mRNAs in sympathetic neurons

Abstract

ABSTRACTBackgroundNeurons are morphologically complex cells that rely on the compartmentalization of protein expression to develop and maintain their cytoarchitecture. Targeting of RNA transcripts to axons is one of the mechanisms that allows rapid local translation of proteins in response to extracellular signals. 3’ untranslated regions (UTRs) of mRNA are non-coding sequences that play a critical role in determining transcript localisation and translation by interacting with specific RNA binding proteins (RBPs). However, how 3’UTRs contribute to mRNA metabolism and the nature of RBP complexes responsible for these functions remain elusive.ResultsWe performed 3’ end sequencing of RNA isolated from axons and cell bodies of sympathetic neurons exposed to either Nerve Growth factor (NGF) or Neurotrophin 3 (NT3). NGF and NT3 are growth factors essential for sympathetic neuron development that act through distinct signalling mechanisms. Whereas NT3 is thought to act only locally, NGF signals back from axons to the cell bodies. We discovered that both NGF and NT3 affect transcription and alternative polyadenylation and induce the localisation of specific 3’UTR isoforms to axons. The finding that many transcripts with short 3’UTR were detected only in axons suggest that these may undergo local post-transcriptional remodelling. The integration of our data with CLIP-sequencing data revealed that long 3’UTR isoforms associate with RBP complexes in the nucleus, and once in axons, regulate cytoplasmic 3’ UTR isoform cleavage into shorter isoform.ConclusionsOur findings shed new light on the complex interplay between nuclear polyadenylation, mRNA localisation and local 3’UTR remodelling in developing neurons.Graphical abstract