Role of SoSLIP/FMRP(Fragile X Mental Retardation Protein) complex in translational regulation – So-FragileX

1. Structural approach to investigate the molecular basis of FMRP/SoSLIP interaction
2. Search for mRNAs containing a SoSLIP-like sequence using bioinformatic tools and validating in vitro and in vivo their interaction with FMRP and their role in translational régulation. XWe will use techniques of molecular and cell biology.
3. Search for proteins interacting with SoSLIP RNA structure by MALDI-TOF-TOF mass spectrometry

Up to date we set up the différents parts of the project.

This proposal will allow to get insight into FMRP/SoSLIP (the motif harboured by Sod1mRNA and mediating its interaction with the C-terminal region of FMRP) interaction and the mechanism controlling the expression level of Sod1 in the brain.
Sod1 has anti-oxidative properties and a moderate increase of oxidative stress in the brain of FMR1 knock-out mice has been described. Recently, we performed a combined chemical, biochemical and bioinformatical approach to better characterize the pathways that are altered in the absence of FMRP in different brain regions and we were able to underline the central role of Sod1 in the physiopathology of FXS. Alteration of oxidative stress is involved in many diseases but its control is also important in aging and to activate the immune system. For all these reasons a study focused on the regulation of the expression of Sod1 is of the highest interest in many physiopathological settings.

On this subject:
-Davidovic L, Navratil V, Bonaccorso C.M., post-transcriptional RNA-metabolism and RNA-binding proteins: 3 actors for a complex scenario. Catania M.V., Bardoni B, Dumas M. (2011) – A metabolomic and system biology perspective on the brain of the Fragile X syndrome mouse model. Genome Res. 21, 2190- 2202
-Bechara E, Didiot, MC, Melko M, Davidovic L, Bensaid M, Martin P, Castets M, Pognonec P, Khandjian E, Moine H, Bardoni B. (2009) A Novel Function of Fragile X Mental Retardation Protein in translational activation. PLoS Biology, Jan 20;7(1):e16

Fragile X syndrome (FXS) is the most common form of inherited mental retardation, which is due to the absence of FMRP, an RNA-binding protein involved in several steps of RNA metabolism.
Despite the importance of this function, the mRNA-binding specificity of FMRP is not completely understood. Even if several hundreds of putative mRNAs targets of FMRP have been identified, validation of their direct binding to FMRP and the functional significance of this interaction is lacking. Up to date, 3 RNA motifs have been found to mediate FMRP/RNA interaction: the G-quadruplex, the «kissing complex» and SoSLIP (Sod1 mRNA Stem Loops Interacting with FMRP). No natural kissing-complex-containing mRNAs have been identified but several G-quadruplex-containing mRNAs interacting with FMRP have been characterized. While those motifs induce translational repression in the presence of FMRP, the interaction of FMRP with the motif in Superoxide Dismutase 1 (Sod1) mRNA revealed a new role of FMRP as a positive modulator of translation. SoSLIP is folded as three independent stem-loop structures and FMRP induces its structural modification. SoSLIP also behaves by itself as a translational activator, and its action is further potentiated by interaction with FMRP. The absence of FMRP in neuronal cells results in a decreased expression of Sod1. Our project aims to decipher the role of FMRP as translational modulator. Up to now FMRP was proposed as a translational repressor, our demonstration of its role in translation activation is raising many new questions. Indeed, the interaction of FMRP with a G-quadruplex RNA forming structure localized in the 5’UTR of an mRNA results in the translational repression of this mRNA (e.g. MAP1B, PP2Ac). This behaviour is opposite to that of a SoSLIP-containing mRNA. Thus, understanding how SoSLIP/FMRP or G-quartet/FMRP complexes are organized in 3D and interact with the different actors of translational regulation (polyribosomes and possibly other factors regulating translation) will enable us to understand the mechanism of this process. For this reason, knowing the structure of SoSLIP and SoSLIP/FMRP complex is essential. Since SoSLIP appears as a novel actor implicated in translational regulation, we are also interested to identify SoSLIP-interacting and -modulating proteins other than FMRP and its homologs. Last, but not least, this project will also allow to identify and characterize new RNA targets of FMRP and open new avenues for therapies for FXS. Indeed, relying on the hypothesis that some sequence and/or structural elements of the SoSLIP motif are necessary to make the interaction between FMRP and mRNA possible, we propose to use a bioinformatics approach to identify novel mRNAs containing a SoSLIP-like structure and then validate them experimentally.
In this project the collaboration between scientists with different backgrounds will allow us to explore different aspects: structure, molecular basis of translational regulation at neuronal soma and synaptic level, in silico search for novel target sequences and their validation in vitro and in vivo.