A Drosophila model of ALS reveals a partial loss of function of causative human PFN1 mutants

Mutations in the profilin 1 (PFN1) gene are causative for familial amyotrophic lateral sclerosis (fALS). However, it is still not fully understood how these mutations lead to neurodegeneration. To address this question, we generated a novel Drosophila model expressing human wild-type and ALS-causative PFN1 mutants. We show that at larval neuromuscular junctions (NMJ), motor neuron expression of wild-type human PFN1 increases the number of ghost boutons, active zone density, F-actin content, and the formation of filopodia. In contrast, the expression of ALS-causative human PFN1 mutants causes a less pronounced phenotype, suggesting a loss of function of these mutants in promoting NMJ remodeling. Importantly, expression of human PFN1 in motor neurons results in progressive locomotion defects and shorter lifespan in adult flies, while ALS-causative PFN1 mutants display a less toxic effect. In summary, our study provides evidence that PFN1 is important in regulating NMJ morphology and influences survival and locomotion in Drosophila. Furthermore, our results suggest ALS-causative human PFN1 mutants display a partial loss of function relative to wild-type hPFN1 that may contribute to human disease pathogenesis.