Localization of FMRP‐associated mRNA granules and requirement of microtubules for activity‐dependent trafficking in hippocampal neurons

Abstract

Fragile X syndrome is caused by the absence of the fragile X mental-retardation protein (FMRP), an mRNAbinding protein, which may play important roles in the regulation of dendritic mRNA localization and/or synaptic protein synthesis. We have recently applied highresolution fluorescence imaging methods to document the presence, motility and activity-dependent regulation of FMRP granule trafficking in dendrites and spines of cultured hippocampal neurons. In this study, we show that FMRP granules distribute to F-actin-rich compartments, including filopodia, spines and growth cones during the staged development of hippocampal neurons in culture. Fragile X mental-retardation protein granules were shown to colocalize with ribosomes, ribosomal RNA and MAP1B mRNA, a known FMRP target, which encodes a protein important for microtubule and actin stabilization. The levels of FMRP within dendrites were reduced by disruption of microtubule dynamics, but not by disruption of F-actin. Direct measurements of FMRP transport kinetics using fluorescence recovery after photobleaching in living neurons showed that microtubules were required to induce the mGluR-dependent translocation into dendrites. This study provides further characterization of the composition and regulated trafficking of FMRP granules in dendrites of hippocampal neurons.

The RNA binding and transport proteins staufen and fragile X mental retardation protein are expressed by rat primary afferent neurons and localize to peripheral and central axons

“…FMRP binds and is involved in transport of RNA to synapses, where it also regulates translation (for review, see Antar and Bassell, 2003). FMRP is critically involved in synaptic plasticity, acting downstream of group I metabo-tropic glutamate receptors to regulate synapse-specific RNA translocation and translation (Antar et al, 2004(Antar et al, ,2005Bear et al, 2004;Weiler et al, 2004;Aschrafi et al, 2005). We have demonstrated here that stau is expressed by neurons in the DRG and TG of the rat and in the human TG.…”

De novo microduplication of the FMR1 gene in a patient with developmental delay, epilepsy and hyperactivity

“…13 The most common mechanism leading to fragile X syndrome is a CGG trinucleotide repeat expansion in the promoter region of the FMR1 gene leading to methylation of the promoter of the gene, with subsequent silencing of transcription and the absence of the encoded product FMRP, 14 which is important for synaptic plasticity and synaptic protein synthesis. 15,16 However, other loss-of-function mutations, including deletions, missense mutations and splice-site mutations, have been reported. [17][18][19][20] The case described here has an 86-kb microduplication that only encompasses the FMR1 and ASFMR1 genes.…”

Rescue of behavioral phenotype and neuronal protrusion morphology in Fmr1 KO mice

“…In most cases, the lack of expression is caused by expansion of a CGG repeat (>200 units) in the 5′ UTR of the FMR1 gene, leading to methylation of both the CGG repeat and the promoter region, accompanied by transcriptional silencing. FMRP is an RNA binding protein that associates with polyribosomes and is localized in neurons in the form of granules that move in a microtubule dependent manner with the speed of RNA transport (Antar et al, 2005;De Diego Otero et al, 2002;Wang et al, 2007). Moreover, FMRP has been shown to influence the translation efficacy of several of its target mRNAs (reviewed in (Bagni and Greenough, 2005;Bardoni et al, 2006;Zalfa et al, 2007), which also implicates local translation at synaptic sites (Greenough et al, 2001;Muddashetty et al, 2007;Weiler et al, 1997;Weiler et al, 2004).…”