Genes and pathways affected by CAG-repeat RNA-based toxicity in Drosophila

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Spinocerebellar ataxia type 3 (SCA3) is a polyglutamine (polyQ) disease caused by CAG-repeat expansion.
• While protein toxicity is traditionally studied, recent findings implicate CAG-repeat RNA in SCA3 pathogenesis.
• Understanding RNA toxicity mechanisms is crucial for developing effective therapies.

Purpose of the Study:

• To investigate the nature of RNA toxicity in SCA3 using a Drosophila model.
• To identify genes and pathways affected by toxic CAG-repeat RNA.
• To explore potential therapeutic targets by examining modifiers of RNA toxicity.

Main Methods:

• Differential gene expression analysis using microarrays on brain-enriched RNA from Drosophila expressing toxic (CAG100) and non-toxic (CAA/G105) repeat mRNA.
• Functional annotation clustering of differentially expressed genes.
• Assessment of heat shock protein 70 (Hsp70) and other protein modifiers on RNA toxicity.

Main Results:

• Microarray analysis identified 160 differentially expressed genes in CAG100 flies, enriched in iron ion and nucleotide binding ontologies.
• Transcripts for Hsp70 genes were upregulated, and Hsp70 was shown to mitigate CAG-repeat RNA toxicity.
• Co-chaperone Tpr2, transcriptional regulator Dpld, and RNA-binding protein Orb2 modified both polyQ protein and CAG-repeat RNA toxicity.

Conclusions:

• CAG-repeat RNA contributes to polyglutamine disease toxicity independently of protein toxicity.
• Upregulation of Hsp70 can suppress RNA-mediated toxicity.
• Identified modifiers suggest an overlap in molecular mechanisms underlying RNA and protein toxicity in polyQ diseases.