Conserved 3'-untranslated region sequences direct subcellular localization of chaperone protein mRNAs in neurons.

Overview

mRNA localization provides polarized cells with a locally renewable source of proteins. In neurons, mRNA translation can occur at millimeters to centimeters from the cell body, giving the dendritic and axonal processes a means to autonomously respond to their environment. Despite that hundreds of mRNAs have been detected in neuronal processes, there are no reliable means to predict mRNA localization elements. Here, we have asked what RNA elements are needed for localization of transcripts encoding endoplasmic reticulum chaperone proteins in neurons. The 3'-untranslated regions (UTRs) of calreticulin and Grp78/BiP mRNAs show no homology to one another, but each shows extensive regions of high sequence identity to their 3'UTRs in mammalian orthologs. These conserved regions are sufficient for subcellular localization of reporter mRNAs in neurons. The 3'UTR of calreticulin has two conserved regions, and either of these is sufficient for axonal and dendritic targeting. However, only nucleotides 1315-1412 show ligand responsiveness to neurotrophin 3 (NT3) and myelin-associated glycoprotein (MAG). This NT3- and MAG-dependent axonal mRNA transport requires activation of JNK, both for calreticulin mRNA and for other mRNAs whose axonal levels are commonly regulated by NT3 and MAG.