Trapping of messenger RNA by Fragile X Mental Retardation protein into cytoplasmic granules induces translation repression.

Publication Type:

Journal Article

Authors:

Mazroui, Rachid; Huot, Marc-Etienne; Tremblay, Sandra; Filion, Christine; Labelle, Yves; E W Khandjian

Source:

Hum Mol Genet, Volume 11, Issue 24, p.3007-17 (2002)

Keywords:

Cytoplasmic Granules, Fluorescent Antibody Technique, Gene Expression Regulation, Genes, Reporter, HeLa Cells, Humans, In Vitro Techniques, Polyribosomes, Protein Biosynthesis, RNA, Messenger, RNA-Binding Proteins

Abstract:

<p>Absence of Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein, is responsible for the Fragile X syndrome, the most common form of inherited mental retardation. FMRP is a cytoplasmic protein associated with mRNP complexes containing poly(A)+mRNA. As a step towards understanding FMRP function(s), we have established the immortal STEK Fmr1 KO cell line and showed by transfection assays with FMR1-expressing vectors that newly synthesized FMRP accumulates into cytoplasmic granules. These structures contain mRNAs and several other RNA-binding proteins. The formation of these cytoplasmic granules is dependent on determinants located in the RGG domain. We also provide evidence that FMRP acts as a translation repressor following co-transfection with reporter genes. The FMRP-containing mRNPs are dynamic structures that oscillate between polyribosomes and cytoplasmic granules reminiscent of the Stress Granules that contain repressed mRNAs. We speculate that, in neurons, FMRP plays a role as a mRNA repressor in incompetent mRNP granules that have to be translocated from the cell body to distal locations such as dendritic spines and synaptosomes.</p>