Disruption of ALS-linked genes and its effect on neuromuscular performance in Drosophila

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disorder of the upper and lower motor neurons, characterized by muscle atrophy. In a study conducted on Maltese ALS patients, damaging variants were only found in the genes that are an infrequent cause of ALS, including ATXN2, SCFD1, DAO, and DCTN1. These so called ‘minor’ ALS genes have not been studied as extensively as genes that are responsible for the majority of familial ALS cases. The study utilised the fruit fly Drosophila as a model organism to disrupt the four genes under investigation, using the GAL4/Upstream Activating Sequence (UAS) genetic system, mostly through RNAi-mediated knockdown. The mobility and viability of flies was assessed when the different transgenes of ATXN2, DCTN1, DAO, and SCFD1 were expressed ubiquitously in the fly, using Act5C-GAL4 driver, or within specific tissues, namely the brain, using elav-GAL4 driver, and muscle tissue, by means of Mef2-GAL4 driver. Disruption of most transgenes tested resulted in significantly decreased larval mobility and extensive reduction in adult fly viability. The expression of ATXN2 polyglutamine expansions and the knockdown of the orthologue Atx2 were found to reduce larval mobility and decrease adult viability, with the observations being exacerbated within muscle tissue, providing evidence for significant roles the gene might have in adequate muscle function. The impact of the ATXN2 polyglutamine expansions were found to be dose-dependent. The DCTN1-p150Glued gene was not required for neuromuscular function within the muscle tissue, but might be required in other tissues. Disruption of Daao1 and Slh, the Drosophila orthologs of DAO and SCFD1, respectively, also resulted in considerable neuromuscular defects. The impact of disturbances in these two genes was observed at various stages of larval development, according to the target location of the transgenes, and highlighted the heterogeneity in transgene expression. The results of this study thus provide fruitful information regarding the significance of ATXN2, DCTN1, DAO, and SCFD1 genes in the pathogenesis of ALS-associated neuromuscular degeneration, and their possible role within various tissues. The observations made during this study form the foundation for future studies aimed at providing further insights into pathophysiological mechanisms associated with mutations within these genes, with this potentially leading to novel therapeutic strategies.