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Dominant, toxic gain-of-function mutations in gars lead to non-cell autonomous neuropathology.

ABSTRACT: Charcot-Marie-Tooth (CMT) neuropathies are collectively the most common hereditary neurological condition and a major health burden for society. Dominant mutations in the gene GARS, encoding the ubiquitous enzyme, glycyl-tRNA synthetase (GlyRS), cause peripheral nerve degeneration and lead to CMT disease type 2D. This genetic disorder exemplifies a recurring motif in neurodegeneration, whereby mutations in essential, widely expressed genes have selective deleterious consequences for the nervous system. Here, using novel Drosophila models, we show a potential solution to this phenomenon. Ubiquitous expression of mutant GlyRS leads to motor deficits, progressive neuromuscular junction (NMJ) denervation and pre-synaptic build-up of mutant GlyRS. Intriguingly, neuronal toxicity is, at least in part, non-cell autonomous, as expression of mutant GlyRS in mesoderm or muscle alone results in similar pathology. This mutant GlyRS toxic gain-of-function, which is WHEP domain-dependent, coincides with abnormal NMJ assembly, leading to synaptic degeneration, and, ultimately, reduced viability. Our findings suggest that mutant GlyRS gains access to ectopic sub-compartments of the motor neuron, providing a possible explanation for the selective neuropathology caused by mutations in a widely expressed gene.

SUBMITTER: Grice SJ

PROVIDER: S-EPMC4492401 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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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).

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Dominant, toxic gain-of-function mutations in gars lead to non-cell autonomous neuropathology.

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