A Genome-Wide Collection of Mos1 Transposon Insertion Mutants for the C. elegans Research Community

Methods that use homologous recombination to engineer the genome of C. elegans commonly use strains carrying specific insertions of the heterologous transposon Mos1. A large collection of known Mos1 insertion alleles would therefore be of general interest to the C. elegans research community. We describe here the optimization of a semi-automated methodology for the construction of a substantial collection of Mos1 insertion mutant strains. At peak production, more than 5,000 strains were generated per month. These strains were then subject to molecular analysis, and more than 13,300 Mos1 insertions characterized. In addition to targeting directly more than 4,700 genes, these alleles represent the potential starting point for the engineered deletion of essentially all C. elegans genes and the modification of more than 40% of them. This collection of mutants, generated under the auspices of the European NEMAGENETAG consortium, is publicly available and represents an important research resource

Author Correction: DRP-1-mediated apoptosis induces muscle degeneration in dystrophin mutants

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Modulation of Protein Quality Control and Proteasome to Autophagy Switch in Immortalized Myoblasts from Duchenne Muscular Dystrophy Patients

The maintenance of proteome integrity is of primary importance in post-mitotic tissues such as muscle cells; thus, protein quality control mechanisms must be carefully regulated to ensure their optimal efficiency, a failure of these processes being associated with various muscular disorders. Duchenne muscular dystrophy (DMD) is one of the most common and severe forms of muscular dystrophies and is caused by mutations in the dystrophin gene. Protein quality control modulations have been diversely observed in degenerating muscles of patients suffering from DMD or in animal models of the disease. In this study, we investigated whether modulations of protein quality control mechanisms already pre-exist in undifferentiated myoblasts originating from DMD patients. We report for the first time that the absence of dystrophin in human myoblasts is associated with protein aggregation stress characterized by an increase of protein aggregates. This stress is combined with BAG1 to BAG3 switch, NFκB activation and up-regulation of BAG3/HSPB8 complexes that ensure preferential routing of misfolded/aggregated proteins to autophagy rather than to deficient 26S proteasome. In this context, restoration of pre-existing alterations of protein quality control processes might represent an alternative strategy for DMD therapies

Ultra-structural time-course study in the C. elegans model for Duchenne muscular dystrophy highlights a crucial role for sarcomere-anchoring structures and sarcolemma integrity in the earliest steps of the muscle degeneration process

International audienceDuchenne muscular dystrophy (DMD) is a genetic disease characterized by progressive muscle degeneration due to mutations in the dystrophin gene. In spite of great advances in the design of curative treatments, most patients currently receive palliative therapies with steroid molecules such as prednisone or deflazacort thought to act through their immunosuppressive properties. These molecules only slightly slow down the progression of the disease and lead to severe side effects. Fundamental research is still needed to reveal the mechanisms involved in the disease that could be exploited as therapeutic targets. By studying a Caenorhabditis elegans model for DMD, we show here that dystrophin-dependent muscle degeneration is likely to be cell autonomous and affects the muscle cells the most involved in locomotion. We demonstrate that muscle degeneration is dependent on exercise and force production. Exhaustive studies by electron microscopy allowed establishing for the first time the chronology of subcellular events occurring during the entire process of muscle degeneration. This chronology highlighted the crucial role for dystrophin in stabilizing sarcomeric anchoring structures and the sarcolemma. Our results suggest that the disruption of sarcomeric anchoring structures and sarcolemma integrity, observed at the onset of the muscle degeneration process, triggers subcellular consequences that lead to muscle cell death. An ultra-structural analysis of muscle biopsies from DMD patients suggested that the chronology of subcellular events established in C. elegans models the pathogenesis in human. Finally, we found that the loss of sarcolemma integrity was greatly reduced after prednisone treatment suggesting a role for this molecule in plasma membrane stabilization

Chemical genetics unveils a key role of mitochondrial dynamics, cytochrome c release and ip3r activity in muscular dystrophy

Duchenne muscular dystrophy (DMD) is a neuromuscular disease caused bymutations in the dystrophin gene.The subcellular mechanisms of DMD remain poorly understood and there is currently no curative treatmentavailable. Using a Caenorhabditis elegans model for DMD as a pharmacologic and genetic tool, we found thatcyclosporineA(CsA) reducesmuscledegeneration atlowdoseandacts, at least in part, through amitochondrialcyclophilin D, CYN-1. We thus hypothesized that CsA acts on mitochondrial permeability modulation throughcyclophilin D inhibition. Mitochondrial patterns and dynamics were analyzed, which revealed dramatic mitochondrialfragmentation not only in dystrophic nematodes, but also in a zebrafish model forDMD.This abnormalmitochondrial fragmentation occurs before any obvious sign of degeneration can be detected. Moreover, wedemonstrate that blocking/delaying mitochondrial fragmentation by knocking down the fission-promotinggene drp-1 reduces muscle degeneration and improves locomotion abilities of dystrophic nematodes.Further experiments revealed that cytochrome c is involved in muscle degeneration in C. elegans and seemsto act, at least in part, through an interaction with the inositol trisphosphate receptor calcium channel, ITR-1.Altogether, our findings reveal that mitochondria play a key role in the early process of muscle degenerationand may be a target of choice for the design of novel therapeutics for DMD. In addition, our results providethe first indication in the nematode that (i) mitochondrial permeability transition can occur and (ii) cytochromec can act in cell death