In eukaryotes, the post-transcriptional regulation of gene expression is based on intricate network of RNA and proteins interactions. For example, messenger RNAs (mRNA) must contain a complete open reading frame, but also the information that specifies their sub cellular localization, translation, and stability. Much of this information is carried by the proteins that cover mRNAs to form mRNA-protein (mRNP) particles, considered as the functional forms in which mRNAs exist in cells. For this reason, numerous pathologies are associated to defect in RNA binding proteins. An important challenge consists in understanding the mechanisms that orchestrate RNP assembly and the role played by the molecular motors that ensure their dynamics.
The group is studying the multiprotein exon junction complex (EJC) deposited onto nuclear mRNAs by the splicing machinery. The EJC composed of a dozen proteins accompanies mRNAs to the cytoplasm. During this travel, it communicates with cellular machineries involved in transport, translation, and quality control of mRNAs. This group combines biochemistry, biophysics, molecular and cellular biology as well as transcriptomic approaches to study EJC assembly and functions.
This group first reconstituted the EJC core with recombinant proteins and solved its tridimensional structure. Hence, they showed how the RNA helicase eIF4AIII and its partners Y14, Magoh and MLN51 stably binds RNA in a sequence independent manner, revealing the first example of a RNA helicase used as a "RNA clamp”. They also showed that the EJC core serves as a binding platform to recruit factors involved in translation and NMD ("nonsense-mediated mRNA decay"), a quality control pathway that eliminates aberrant mRNAs.
More recently, they combined strategies of RNA-protein complexes purification and large-scale RNA sequencing to establish the first map of EJC binding sites in human cells. They now use this approach to study EJC assembly in different cellular contexts.
Every RNA-dependent processes necessitate RNA helicases that use the energy of ATP hydrolysis to unwind RNA structures or to remodel RNA-protein interactions. If these molecular motors are essential, their action mode and their targets are often unknown. This group combines biochemical and biophysical tools to characterize at the scale of single molecules the properties of RNA helicases like Upf1 that is essential for NMD.
Kwon OS, Mishra R, Safieddine A, Coleno E, Alasseur Q, Faucourt M, Barbosa I, Bertrand E, Spassky N, Le Hir H. Exon Junction Complex dependent mRNA localization is linked to centrosome organization during ciliogenesis. Nat Commun. 2021 Mar 1;12(1):1351.
Busetto V, Barbosa I, Basquin J, Marquenet É, Hocq R, Hennion M, Paternina JA, Namane A, Conti E, Bensaude O, Le Hir H. Structural and functional insights into CWC27/CWC22 heterodimer linking the exon junction complex to spliceosomes. Nucleic Acids Res. 2020 48(10):5670-5683.
Kanaan J, Raj S, Decourty L, Saveanu C, Croquette V, Le Hir H. UPF1-like helicase grip on nucleic acids dictates processivity. Nature Communications. 2018 9(1):3752.
Le Hir H, Saulière J, Wang Z. The exon junction complex as a node of postranscriptional networks. Nature Reviews in Molecular and Cellular Biology. 2016 Jan;17(1):41-54.
Fiorini F, Bagchi D, Le Hir H, Croquette V. Human Upf1 is a highly processive RNA helicase and translocase with RNP remodelling activities. Nature Communications. 2015 Jul 3;6:7581.
Wang Z, Murigneux V, Le Hir H. Transcriptome-wide modulation of splicing by the Exon Junction Complex. Genome Biol. 2014 Dec 5;15(12):551.
Saulière J, Murigneux V, Wang Z, Marquenet E, Barbosa I, Le Tonquèze O, Audic Y, Paillard L, Roest Crollius H, Le Hir H. CLIP-seq of eIF4AIII reveals transcriptome-wide mapping of the human exon junction complex. Nature Structural and Molecular Biology (2012) 19(11):1124-31.
Barbosa I, Haque N, Fiorini F, Barrandon C, Tomasetto C, Blanchette M, Le Hir H. Human CWC22 escorts the helicase eIF4AIII to spliceosomes and promotes exon junction complex assembly. Nature Structural and Molecular Biology (2012) 19(10):983-90.
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