Cytoplasmic cleavage of IMPA1 3′ UTR is necessary for maintaining axon integrity

Catia Andreassi,Raphaëlle Luisier,Hamish Crerar,Marousa Darsinou,Sasja Blokzijl-Franke,Tchern Lenn,Nicholas M Luscombe,Giovanni Cuda,Marco Gaspari,Adolfo Saiardi,Antonella Riccio

doi:10.1016/j.celrep.2021.108778

Abstract

SummaryThe 3′ untranslated regions (3′ UTRs) of messenger RNAs (mRNAs) are non-coding sequences involved in many aspects of mRNA metabolism, including intracellular localization and translation. Incorrect processing and delivery of mRNA cause severe developmental defects and have been implicated in many neurological disorders. Here, we use deep sequencing to show that in sympathetic neuron axons, the 3′ UTRs of many transcripts undergo cleavage, generating isoforms that express the coding sequence with a short 3′ UTR and stable 3′ UTR-derived fragments of unknown function. Cleavage of the long 3′ UTR of Inositol Monophosphatase 1 (IMPA1) mediated by a protein complex containing the endonuclease argonaute 2 (Ago2) generates a translatable isoform that is necessary for maintaining the integrity of sympathetic neuron axons. Thus, our study provides a mechanism of mRNA metabolism that simultaneously regulates local protein synthesis and generates an additional class of 3′ UTR-derived RNAs.

Highlights

Asymmetric localization of RNA is an evolutionarily conserved mechanism that allows spatial restriction of protein synthesis to cellular compartments
Identification of 30 untranslated regions (30 untranslated regions (UTRs)) isoforms in axons and cell bodies of sympathetic neurons To characterize the 30 UTR isoforms localized in cell bodies or axons of rat sympathetic neurons, we performed stranded 30 end RNA sequencing (RNA-seq) using messenger RNAs (mRNAs) isolated from neurons grown in compartmentalized chambers (Figure S1A)
MRNA was subject to two rounds of linear amplification (Figure S1B) that led to the accumulation of reads at the 30 end of transcripts independently of the 30 UTR length (Figures 1A and S1C), generating a read coverage profile similar to poly(A)-seq (Shepard et al, 2011)

Summary

Introduction

Asymmetric localization of RNA is an evolutionarily conserved mechanism that allows spatial restriction of protein synthesis to cellular compartments. Isoforms of the BDNF transcript with either short or long 30 UTRs are localized to dendrites in response to extracellular cues (Allen et al, 2013; An et al, 2008; Will et al, 2013). Despite all of this evidence, how mRNA metabolism is regulated in neurons and the role of the 30 UTR in determining the translation of transcripts necessary for neuronal functions remain largely unknown

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Conclusion