Highlights d Axons and cell bodies of sympathetic neurons express distinct 3 0 UTR isoforms d Axon-specific short 3 0 UTR isoforms are generated by local cleavage of longer 3 0 UTRs d A protein complex containing Ago2, Upf1, HuD, and Pabpc4 mediates the 3 0 UTR cleavage

The neural crest is a dynamic progenitor cell population that arises at the border of neural and non-neural ectoderm. The inductive roles of FGF, Wnt, and BMP at the neural plate border are well established, but the signals required for subsequent neural crest development remain poorly characterized. Here, we conducted a screen in primary zebrafish embryo cultures for chemicals that disrupt neural crest development, as read out by crestin:EGFP expression. We found that the natural product caffeic acid phenethyl ester (CAPE) disrupts neural crest gene expression, migration, and melanocytic differentiation by reducing Sox10 activity. CAPE inhibits FGF-stimulated PI3K/Akt signaling, and neural crest defects in CAPE-treated embryos are suppressed by constitutively active Akt1. Inhibition of Akt activity by constitutively active PTEN similarly decreases crestin expression and Sox10 activity. Our study has identified Akt as a novel intracellular pathway required for neural crest differentiation.

2Asymmetric localization of mRNAs is a mechanism that constrains protein synthesis to subcellular compartments. In neurons, mRNA transcripts are transported to both dendrites and axons where they are rapidly translated in response to extracellular stimuli. To characterize the 3'UTR isoforms localized in axons and cell bodies of sympathetic neurons we performed 3'end-RNA sequencing. We discovered that isoforms transported to axons had significantly longer 3'UTRs compared to cell bodies. Moreover, more than 100 short 3'UTR isoforms were uniquely expressed in axons. Analysis of the long 3'UTR of IMPA1 indicated that a multiprotein complex including Upf1, HuD and Ago2 mediated 3'UTR cleavage. This event enhanced IMPA1 translation and was necessary for maintaining axon integrity. 3'UTR cleavage took place in axons and was not limited to IMPA1 but extended to other transcripts with similar expression patterns. We conclude that the 3'UTR of neuronal transcripts undergo post-transcriptional remodelling and describe an alternative mechanism that regulates local protein synthesis KEYWORDS 3'UTR remodelling; sympathetic neurons; RNA localization; axons; alternative polyadenylation; local protein synthesis . CC-BY-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/170100 doi: bioRxiv preprint first posted online 3 HIGHLIGHTS• 3'end-Seq reveals distinct expression of alternative 3'UTR isoforms in axons and cell bodies of sympathetic neurons.• Short 3'UTR isoforms uniquely detected in axons are generated in situ by cleavage of longer precursors.• A protein complex containing Upf1, HuD, Pabpc4 and Ago2 mediates the cleavage of 3'UTRs.. CC-BY-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/170100 doi: bioRxiv preprint first posted online 4 INTRODUCTIONNeurons are cells with a complex morphology, which maintain their cellular structure through the compartmentalized expression of proteins essential for growth and plasticity.Asymmetric localization of RNA is an evolutionarily conserved mechanism that allows spatial restriction of protein synthesis to specific cellular compartments. Incorrect processing and delivery of mRNA causes developmental defects and severe human neurological disorders (Holt and Schuman, 2013;Wang et al., 2007). Eukaryotic mRNAs share common features that include exons and introns, 5' and 3' untranslated regions (UTRs), a modified base at the 5' end named "cap", and a stretch of adenosines at the 3' end named poly(A) tail, which confers stability to the transcript preventing premature degradation and enables its translation. The information necessary for RNA processing can be stored anywhere along the transcript, however most elements that regulate mRNA transport and translation are found within the 3' and 5'UTRs. 3'UTRs regulate multiple aspects of m...