Showing papers by "Jean-Louis Mandel published in 2019"

Rare De Novo Missense Variants in RNA Helicase DDX6 Cause Intellectual Disability and Dysmorphic Features and Lead to P-Body Defects and RNA Dysregulation.

Abstract: The human RNA helicase DDX6 is an essential component of membrane-less organelles called processing bodies (PBs). PBs are involved in mRNA metabolic processes including translational repression via coordinated storage of mRNAs. Previous studies in human cell lines have implicated altered DDX6 in molecular and cellular dysfunction, but clinical consequences and pathogenesis in humans have yet to be described. Here, we report the identification of five rare de novo missense variants in DDX6 in probands presenting with intellectual disability, developmental delay, and similar dysmorphic features including telecanthus, epicanthus, arched eyebrows, and low-set ears. All five missense variants (p.His372Arg, p.Arg373Gln, p.Cys390Arg, p.Thr391Ile, and p.Thr391Pro) are located in two conserved motifs of the RecA-2 domain of DDX6 involved in RNA binding, helicase activity, and protein-partner binding. We use functional studies to demonstrate that the first variants identified (p.Arg373Gln and p.Cys390Arg) cause significant defects in PB assembly in primary fibroblast and model human cell lines. These variants' interactions with several protein partners were also disrupted in immunoprecipitation assays. Further investigation via complementation assays included the additional variants p.Thr391Ile and p.Thr391Pro, both of which, similarly to p.Arg373Gln and p.Cys390Arg, demonstrated significant defects in P-body assembly. Complementing these molecular findings, modeling of the variants on solved protein structures showed distinct spatial clustering near known protein binding regions. Collectively, our clinical and molecular data describe a neurodevelopmental syndrome associated with pathogenic missense variants in DDX6. Additionally, we suggest DDX6 join the DExD/H-box genes DDX3X and DHX30 in an emerging class of neurodevelopmental disorders involving RNA helicases.

Novel mutations in NLGN3 causing autism spectrum disorder and cognitive impairment.

Abstract: The X-linked NLGN3 gene, encoding a postsynaptic cell adhesion molecule, was involved in a nonsyndromic monogenic form of autism spectrum disorder (ASD) by the description of one unique missense variant, p.Arg451Cys (Jamain et al. 2003). We investigated here the pathogenicity of additional missense variants identified in two multiplex families with intellectual disability (ID) and ASD: c.1789C>T, p.Arg597Trp, previously reported by our group (Redin et al. 2014) and present in three affected cousins and c.1540C>T, p.Pro514Ser, identified in two affected brothers. Overexpression experiments in HEK293 and HeLa cell lines revealed that both variants affect the level of the mature NLGN3 protein, its localization at the plasma membrane and its presence as a cleaved form in the extracellular environment, even more drastically than what was reported for the initial p.Arg451Cys mutation. The variants also induced an unfolded protein response, probably due to the retention of immature NLGN3 proteins in the endoplasmic reticulum. In comparison, the c.1894A>G, p.Ala632Thr and c.1022T>C, p.Val341Ala variants, present in males from the general population, have no effect. Our report of two missense variants affecting the normal localization of NLGN3 in a total of five affected individuals reinforces the involvement of the NLGN3 gene in a neurodevelopmental disorder characterized by ID and ASD.

Clinical and functional characterization of recurrent missense variants implicated in THOC6-related intellectual disability.

Abstract: THOC6 encodes a subunit of the THO complex that is part of a highly conserved transcription and export complex known to have roles in mRNA processing and export. Few homozygous or compound heterozygous variants have been identified in the THOC6 gene in patients with a syndromic form of intellectual disability [Beaulieu-Boycott-Innes syndrome (BBIS); MIM: 613680]. Here we report two additional individuals affected with BBIS originating from the north of Europe and sharing a haplotype composed of three very rare missense changes in the THOC6 gene-Trp100Arg, Val234Leu, Gly275Asp. The first individual is a boy who is homozygous for the three-variant haplotype due to a maternal uniparental disomy event. The second is a girl who is compound heterozygous for this haplotype and a previously reported Gly190Glu missense variant. We analyzed the impact of these different amino acid changes on THOC6 protein expression, cellular localization and interaction with the other THO complex subunits. We show that the different THOC6 variants alter the physiological nuclear localizationof the protein and its interaction with at least two THO subunits, THOC1 and THOC5. Two amino acid changes from the three-variant haplotype alone have specific effects and might contribute to the pathogenicity of the haplotype. Overall, we expanded the cohort of currently known individuals with BBIS by reporting two individuals carrying the same recurrent European haplotype composed of three amino acid changes, affecting THOC6 localization and interaction with THO protein partners.

Spatial control of nucleoporin assembly by Fragile X-related proteins

Abstract: Summary Nucleoporins (Nups) build highly organized Nuclear Pore Complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs to regulate nucleocytoplasmic exchange. In the cytoplasm, a large excess of soluble Nups has been reported, but how their assembly is restricted to the NE is currently unknown. Here we show that Fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule and dynein-dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and Fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup protein condensates. Likewise, several models of Fragile X syndrome (FXS), characterized by a loss of FMRP, also accumulate cytoplasmic Nup aggregates. These aggregate-containing cells display aberrant nuclear morphology and a delay in G1 cell cycle progression. Our results reveal an unexpected role for the FXR protein family and dynein in the spatial regulation of nucleoporin assembly. Highlights Cytoplasmic nucleoporins are assembled by Fragile X-related (FXR) proteins and dynein FXR-Dynein pathway downregulation induces aberrant cytoplasmic aggregation of nucleoporins Cellular models of Fragile X syndrome accumulate aberrant cytoplasmic nucleoporin aggregates. FXR-Dynein pathway regulates nuclear morphology and G1 cell cycle progression eTOC Blurb Nucleoporins (Nups) form Nuclear Pore Complexes (NPCs) at the nuclear envelope. Agote-Aran at al. show how cells inhibit aberrant assembly of Nups in the cytoplasm and identify Fragile X-related (FXR) proteins and dynein that facilitate localization of Nups to the nuclear envelope and control G1 cell cycle progression.