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Mutant FUS induces chromatin reorganization in the hippocampus and alters memory processes

ABSTRACT: This project aims to assess the transcriptomic signature of FUS∆NLS/+ (FUS) vs FUS+/+ (WT) mice, by identifying differentially expressed genes in basal conditions and also during learning. Cytoplasmic mislocalization of the nuclear Fused in Sarcoma (FUS) protein is associated to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Cytoplasmic FUS accumulation is recapitulated in the frontal cortex and spinal cord of heterozygous Fus∆NLS/+ mice. We show that in these mice, the hippocampus, a critical structure involved in learning and memory, paradoxically displays nuclear FUS accumulation. FUS binds to a set of genes characterized by the presence of an ETS/ELK-binding motifs, and involved in RNA metabolism, transcription, ribosome/mitochondria and chromatin organization. Importantly, hippocampal nuclei showed a decompaction of the neuronal chromatin at highly expressed genes and an inappropriate transcriptomic response was observed after spatial training of Fus∆NLS/+ mice. Furthermore, these mice lacked precision in hippocampal-dependent spatial memory task. These studies shows that mutated FUS affects epigenetic regulation of the chromatin landscape in hippocampal neurons, which could participate in FTD/ALS pathogenic events.

ORGANISM(S): Mus musculus

PROVIDER: GSE218226 | GEO | 2024/11/30

REPOSITORIES: GEO

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Project description:FUS is an RNA-binding protein involved in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Cytoplasmic FUS-containing aggregates are often associated with concomitant loss of nuclear FUS. Whether loss of nuclear FUS function, gain of a cytoplasmic function, or a combination of both lead to neurodegeneration remains elusive. To address this question, we generated knock-in mice expressing mislocalized cytoplasmic FUS and complete FUS knock-out mice. Both mouse models display similar perinatal lethality with respiratory insufficiency, reduced body weight and length, and largely similar alterations in gene expression and mRNA splicing patterns, indicating that mislocalized FUS results in loss of its normal function. However, FUS knock-in mice, but not FUS knock-out mice, display reduced motor neuron numbers at birth, associated with enhanced motor neuron apoptosis, which can be rescued by cell-specific CRE-mediated expression of wild-type FUS within motor neurons. Together, our findings indicate that cytoplasmic FUS mislocalization not only leads to nuclear loss of function, but also triggers motor neuron death through a toxic gain of function within motor neurons. Total RNA from brains of E18.5 knock-in (FusÎNLS/ÎNLS), and knock-out (Fus-/-) mice and their control littermates were extracted with Trizol and libraries were prepared for RNA sequencing and RNA-mediated oligonucleotide Annealing, Selection, and Ligation with Next-Generation sequencing (RASL-seq) (Li et al. 2012; Zhou et al. 2012). For the RNA-seq experiment, biological replicates were used with n=4-5 knock-in animals per group (4 wild-type and 5 homozygous FusÎNLS) and n=5 knock-out animals per group (5 wild-type and 5 homozygous Fus-/-). For the RASL-seq analysis, biological replicates were used with n=4 knock-in animals per group (4 wild-type, 4 heterozygous and 4 homozygous FusÎNLS) and n=5 animals per group (5 wild-type and 5 homozygous Fus-/- knock-out).

Project description:Through the generation of humanized FUS mice expressing full length human FUS, we identify that when expressed at near endogenous murine FUS levels both wild-type or ALS- and frontotemporal dementia (FTD)-causing mutations complement the essential function(s) of murine FUS. Replacement of murine FUS with mutant, but not wild-type, human FUS causes stress-mediated induction of chaperones, decreased expression of ion channels/transporters essential for synaptic function, and reduced synaptic activity, without loss of nuclear FUS or its cytoplasmic aggregation. Most strikingly, accumulation of mutant human FUS is shown to activate an integrated stress response and inhibit local, intra-axonal protein synthesis in hippocampal neurons and sciatic nerves. Collectively, our evidence demonstrates that human ALS/FTD-linked mutations in FUS induce a gain-of-toxicity that includes stress-mediated suppression in intra-axonal translation, synaptic dysfunction, and progressive, age-dependent motor and cognitive disease without cytoplasmic aggregation, altered nuclear localization, or aberrant splicing of FUS-bound pre-mRNAs. Methods: RNA from mouse spinal cords of 18-month-old mFUS-/-/hgFUS (WT, R521C or R521H) and their Non-Tg control littermates was extracted with TRIzol. RNA quality was measured using the Agilent Bioanalyzer system and processed using the Illumina TruSeq Stranded mRNA Sample Preparation Kit according to manufacturer’s protocols. mRNA profiles were generated by deep sequencing, with n≥3 biological replicates per group. Results: We mapped on average 15 million non-redundant reads per sample. Fastq files were aligned to mouse reference genome (mm9 UCSC Genome Browser) using TopHat workfow and the transcript abundance for each annotated protein-coding gene [as fragments per kilobase of transcript per million mapped reads (FPKM)] was estimated by Cufflinks. 13,468 genes which expressed FPKM>=1 were kept for downstream analyses. RNA profiles from normal (Non-Tg) and humanized hgFUSWT mice were almost undistinguishable. Both humanized mutant FUS lines had highly distinct RNA profiles [determined with unsupervised hierarchical clustering and principal component analysis (PCA)], with 709 down and 348 up-regulated genes relative to age-matched Non-Tg or humanized hgFUSWT littermates (P<0.05). These changes uncovered FUS mutant dependent altered pathways that may contribute to ALS/FTD-linked mutant FUS-mediated toxicity. The validation by RT-QPCR of altered expression of 20 genes is shown in Figure 5.

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Mutant FUS induces chromatin reorganization in the hippocampus and alters memory processes

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