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Updated: Nov 3, 2025
Measuring RAN Peptide Toxicity in C. elegans
Published on: April 30, 2020
Toxicity of pathogenic ataxin-2 in Drosophila shows dependence on a pure CAG repeat sequence
Leeanne McGurk1,2, Olivia M Rifai2, Oksana Shcherbakova2
1Division of Cell & Developmental Biology, School of Life Sciences, University of Dundee, Dundee, UK.
Abstract:
Spinocerebellar ataxia type 2 is a polyglutamine (polyQ) disease associated with an expanded polyQ domain within the protein product of the ATXN2 gene. Interestingly, polyQ repeat expansions in ATXN2 are also associated with amyotrophic lateral sclerosis (ALS) and parkinsonism depending upon the length of the polyQ repeat expansion. The sequence encoding the polyQ repeat also varies with disease presentation: a pure CAG repeat is associated with SCA2, whereas the CAG repeat in ALS and parkinsonism is typically interrupted with the glutamine encoding CAA codon. Here, we asked if the purity of the CAG sequence encoding the polyQ repeat in ATXN2 could impact the toxicity of the ataxin-2 protein in vivo in Drosophila. We found that ataxin-2 encoded by a pure CAG repeat conferred toxicity in the retina and nervous system, whereas ataxin-2 encoded by a CAA-interrupted repeat or CAA-only repeat failed to confer toxicity, despite expression of the protein at similar levels. Furthermore, the CAG-encoded ataxin-2 protein aggregated in the fly eye, while ataxin-2 encoded by either a CAA/G or CAA repeat remained diffuse. The toxicity of the CAG-encoded ataxin-2 protein was also sensitive to the translation factor eIF4H, a known modifier of the toxic GGGGCC repeat in flies. These data indicate that ataxin-2 encoded by a pure CAG versus interrupted CAA/G polyQ repeat domain is associated with differential toxicity, indicating that mechanisms associated with the purity of the sequence of the polyQ domain contribute to disease.
Insights
The purity of the polyglutamine (polyQ) sequence in the ATXN2 gene impacts spinocerebellar ataxia type 2 (SCA2) toxicity. Pure CAG repeats cause toxicity and aggregation, unlike interrupted repeats.
Area of Science:
- Neurogenetics
- Molecular Biology
- Disease Mechanisms
Background:
- Spinocerebellar ataxia type 2 (SCA2) is a polyglutamine (polyQ) disease linked to ATXN2 gene polyQ expansions.
- ATXN2 polyQ expansions are also implicated in amyotrophic lateral sclerosis (ALS) and parkinsonism.
- Disease presentation differs based on polyQ repeat purity: pure CAG for SCA2, interrupted CAA for ALS/parkinsonism.
Purpose of the Study:
- To investigate if the purity of the CAG sequence encoding the polyQ repeat in ATXN2 affects ataxin-2 protein toxicity in vivo.
- To compare the toxicity of pure CAG repeats versus CAA-interrupted repeats in the ATXN2 gene.
Main Methods:
- Utilized Drosophila models to assess ataxin-2 protein toxicity in the retina and nervous system.
- Compared protein aggregation and toxicity between ataxin-2 variants with pure CAG, CAA-interrupted, and CAA-only polyQ repeats.
- Investigated the role of translation factor eIF4H in modulating CAG-encoded ataxin-2 toxicity.
Main Results:
- Ataxin-2 encoded by a pure CAG repeat demonstrated toxicity in the fly retina and nervous system.
- Ataxin-2 from CAA-interrupted or CAA-only repeats showed no toxicity, despite similar protein expression levels.
- CAG-encoded ataxin-2 aggregated in the fly eye, while CAA-encoded variants remained diffuse.
- Toxicity of CAG-encoded ataxin-2 was modulated by the translation factor eIF4H.
Conclusions:
- The purity of the polyQ repeat sequence in ATXN2 significantly influences ataxin-2 protein toxicity.
- Pure CAG repeats in ATXN2 are associated with neurotoxicity and protein aggregation, characteristic of SCA2.
- Sequence purity, not just repeat length, is a critical factor in polyQ-mediated neurodegenerative diseases.
