[
International Worm Meeting,
2021]
Amyotrophic Lateral Sclerosis (ALS) is characterized by the progressive degeneration of neurons, resulting in chronic muscular atrophy. In 25-40% of familial ALS cases, an inappropriately expanded GGGGCC repeat is found in the first intron of the C9ORF72 gene, resulting in neuron degeneration and eventually death. We generated a new C. elegans model expressing 30 copies of GGGGCC nucleotide repeats at high levels specifically in 8 sensory glutamatergic neurons. Back-filling of the PHA and PHB phasmid sensory neurons with a fluorescent dye revealed that 80% to 90% of 30x(GGGGCC) animals lose neurons or have defective neuron process, but 3x(GGGGCC) animals were relatively unaffected. Given the highly penetrant defect we were able to use this simple assay and perform an unbiased screen to identify genetic suppressors of neurodegeneration. Using EMS, we identified 28 potential suppressor lines in which degeneration of phasmid neurons was partially rescued (between 30 to 70% intact neurons). Of these 28 lines, 23 of them are clearly independent isolate, suggesting they contain unique suppressors mutations. As a secondary screen of the suppressor and to facilitate gene identification, we established a genetic scheme allowing for each line 1/ to test if the EMS hit affected a gene rather than the 30x(GGGGCC) insertion and 2/ Establish independent sub lines carrying the suppressors, named Suppressor lines, and independent lines that derivate from the Suppressor line, named Sibling lines. These Sibling lines have a similar genetic backgrounds i.e. other genes affected by the EMS treatment but will fail to rescue the 30x(GGGGCC) related neuron degeneration, meaning they don't carry the suppressor anymore. These different lines will be sequenced and by using the subtraction method (https://doi.org/10.1534/g3.117.300135) we will establish a list of candidate genes that suppress the neuron degeneration caused by GGGGCC nucleotide expansion. Further tests, using mutants of these candidate genes, will then allow to have crucial insights on genetic modifiers and pathways allowing to alleviate neuron degeneration in ALS.