Deletion of C9ORF72 Results in Motor Neuron Degeneration and Stress Sensitivity in C. elegans

Martine Therrien,Patrick A Dion,Guy A Rouleau,J Alex Parker,Denis Dupuy

doi:10.1371/journal.pone.0083450

Abstract

An expansion of the hexanucleotide GGGGCC repeat in the first intron of C9ORF72 gene was recently linked to amyotrophic lateral sclerosis. It is not known if the mutation results in a gain of function, a loss of function or if, perhaps both mechanisms are linked to pathogenesis. We generated a genetic model of ALS to explore the biological consequences of a null mutation of the Caenorhabditis elegans C9ORF72 orthologue, F18A1.6, also called alfa-1. alfa-1 mutants displayed age-dependent motility defects leading to paralysis and the specific degeneration of GABAergic motor neurons. alfa-1 mutants showed differential susceptibility to environmental stress where osmotic stress provoked neurodegeneration. Finally, we observed that the motor defects caused by loss of alfa-1 were additive with the toxicity caused by mutant TDP-43 proteins, but not by the mutant FUS proteins. These data suggest that a loss of alfa-1/C9ORF72 expression may contribute to motor neuron degeneration in a pathway associated with other known ALS genes.

Highlights

Amyotrophic lateral sclerosis (ALS) is one of the most common neurodegenerative disorders and it is characterized by progressive death of motor neurons in the brain and spinal cord
To either alfa-1(ok3062) or FUSS57∆ alone (Figure 4B and Table S1). These data suggest that the genetic interactions between alfa-1 and TAR DNA binding protein 43 (TDP-43) or FUS are not equivalent, and that perhaps alfa-1 and FUSS57∆ function in the same pathway, while TDP-43 may use parallel or independent pathways resulting in motor neuron dysfunction
Zhang et al have shown that the amino acids most conserved between C9ORF72 and other Differentially Expressed in Normal and Neoplasia” (DENN) proteins are conserved between C9ORF72 and ALFA-1

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is one of the most common neurodegenerative disorders and it is characterized by progressive death of motor neurons in the brain and spinal cord. Alfa-1(ok3062) mutants were more sensitive to aldicarb induced paralysis compared to wild type worms (Figure 2B) These data suggest that alfa-1(ok3062) mutants may have impaired inhibitory GABAergic signalling, perhaps recapitulating the neurotransmitter imbalance observed in ALS patients [16]. Alfa-1(ok3062) had no effect on dauer formation or the long-lived phenotypes of daf-2(e1370) mutants (Figure S2C, D and Table S2) These data suggest that ALFA-1 has a specific role in protecting worms against osmotic stress, perhaps involving the insulin-IGF pathway. The same experiment was carried using alfa-1(RNAi) and similar results were obtained (Figure S2B) These data suggest that the motor neurons of alfa-1(ok3062) animals are sensitive to osmotic stress and that this type of environmental stress may be relevant to the function of C9ORF72. These data suggest that the genetic interactions between alfa-1 and TDP-43 or FUS are not equivalent, and that perhaps alfa-1 and FUSS57∆ function in the same pathway, while TDP-43 may use parallel or independent pathways resulting in motor neuron dysfunction

Discussion

Findings

Materials and Methods