Project description:Spinocerebellar ataxia type 3 (SCA3) is one of the polyglutamine (polyQ) diseases, which are caused by a CAG repeat expansion within the coding region of the associated genes. The CAG repeat specifies glutamine, and the expanded polyQ domain with mutation confers dominant toxicity on the protein. Traditionally, studies have focused on protein toxicity in polyQ disease mechanisms. Recent findings, however, demonstrate that the CAG repeat RNA, which encodes the toxic polyQ protein, also contributes to the disease in Drosophila. To provide insight into the nature of the RNA toxicity, we extracted brain-enriched RNA from flies expressing a toxic CAG repeat mRNA (CAG100) and a non-toxic interrupted CAA/G mRNA repeat (CAA/G105) for microarray analysis. This approach identified a set of genes that are differentially expressed specifically in CAG100 flies.
Project description:Spinocerebellar ataxia type 3 (SCA3) is one of the polyglutamine (polyQ) diseases, which are caused by a CAG repeat expansion within the coding region of the associated genes. The CAG repeat specifies glutamine, and the expanded polyQ domain with mutation confers dominant toxicity on the protein. Traditionally, studies have focused on protein toxicity in polyQ disease mechanisms. Recent findings, however, demonstrate that the CAG repeat RNA, which encodes the toxic polyQ protein, also contributes to the disease in Drosophila. To provide insight into the nature of the RNA toxicity, we extracted brain-enriched RNA from flies expressing a toxic CAG repeat mRNA (CAG100) and a non-toxic interrupted CAA/G mRNA repeat (CAA/G105) for microarray analysis. This approach identified a set of genes that are differentially expressed specifically in CAG100 flies. Four independent replicates of flies expressing CAG0, CAG100, or CAA/G105 by elav-GAL4 were collected at 3 days. The transgenes are DsRed with either (CAG0) no CAG repeat in the 3'UTR, (CAG100) a CAG repeat of 100 CAGs in the 3'UTR, or (CAA/G105) an interrupted CAA CAG repeat in the 3'UTR (ref: Li et al., Nature 453:1107) The transgenes were adjusted to match in mRNA expression such that CAG0 flies had one copy of the transgene, CAG100 flies had 5 copies, and CAA/G105 had two copies. Fly brain tissue (about 20 brains per sample, dissected from head capsule, eyes, lamina and outer medulla removed) was dissected in cold phosphate buffered saline (PBS) and stored in Trizol reagent (Invitrogen Corporation, Carlsbad, CA) at -80Ë?C. Total brain RNA was extracted and purified using TRIzol reagent (Invitrogen) and the RNeasy Mini system (Qiagen), and treated with RNase-free DNase I (Qiagen). To define genes whose expression is altered in response to a toxic CAG repeat RNA, we compared CAG100 flies with age-matched flies expressing CAG0. To exclude transcriptional changes in response to a non-toxic trinucleotide repeat, a second gene list was generated by comparing CAA/G105 flies with age-matched CAG0 flies.
Project description:Distinct roles for Toll and autophagy pathways in double-stranded RNA toxicity in a Drosophila model of expanded repeat neurodegenerative diseases
Project description:Dominantly inherited expanded repeat neurodegenerative diseases are typically caused by the expansion of existing variable copy number tandem repeat sequences in otherwise unrelated genes. Repeats located in translated regions encode polyglutamine that is thought to be the toxic agent, however in several instances the expanded repeat is in an untranslated region, necessitating multiple pathogenic pathways or an alternative common toxic agent. As numerous clinical features are shared by several of these diseases, and expanded repeat RNA is a common intermediary, RNA has been proposed as a common pathogenic agent. Various forms of repeat RNA are toxic in animal models, by multiple distinct pathways. In Drosophila, repeat-containing double-stranded RNA (rCAG.rCUG~100) toxicity is dependent on Dicer processing evident with the presence of single-stranded rCAG7, which have been detected in affected HD brains. Microarray analysis of Drosophila rCAG.rCUG~100 repeat RNA toxicity revealed perturbation of several pathways including innate immunity. Recent reports of elevated circulating cytokines prior to clinical onset, and age-dependent increased inflammatory signaling and microglia activation in the brain, suggest that immune activation precedes neuronal toxicity. Since the Toll pathway is activated by certain forms of RNA, we assessed the role of this pathway in RNA toxicity. We find that rCAG.rCUG~100 activates Toll signaling and that RNA toxicity is dependent on this pathway. The sensitivity of RNA toxicity to autophagy further implicates innate immune activation. Expression of rCAG.rCUG~100 was therefore directed in glial cells and found to be sufficient to cause neuronal dysfunction. Non-autonomous toxicity due to expanded repeat-containing double-stranded RNA mediated activation of innate immunity is therefore proposed as a candidate pathway for this group of human genetic diseases.
Project description:Dominantly inherited expanded repeat neurodegenerative diseases are typically caused by the expansion of existing variable copy number tandem repeat sequences in otherwise unrelated genes. Repeats located in translated regions encode polyglutamine that is thought to be the toxic agent, however in several instances the expanded repeat is in an untranslated region, necessitating multiple pathogenic pathways or an alternative common toxic agent. As numerous clinical features are shared by several of these diseases, and expanded repeat RNA is a common intermediary, RNA has been proposed as a common pathogenic agent. Various forms of repeat RNA are toxic in animal models, by multiple distinct pathways. In Drosophila, repeat-containing double-stranded RNA (rCAG.rCUG~100) toxicity is dependent on Dicer processing evident with the presence of single-stranded rCAG7, which have been detected in affected HD brains. Microarray analysis of Drosophila rCAG.rCUG~100 repeat RNA toxicity revealed perturbation of several pathways including innate immunity. Recent reports of elevated circulating cytokines prior to clinical onset, and age-dependent increased inflammatory signaling and microglia activation in the brain, suggest that immune activation precedes neuronal toxicity. Since the Toll pathway is activated by certain forms of RNA, we assessed the role of this pathway in RNA toxicity. We find that rCAG.rCUG~100 activates Toll signaling and that RNA toxicity is dependent on this pathway. The sensitivity of RNA toxicity to autophagy further implicates innate immune activation. Expression of rCAG.rCUG~100 was therefore directed in glial cells and found to be sufficient to cause neuronal dysfunction. Non-autonomous toxicity due to expanded repeat-containing double-stranded RNA mediated activation of innate immunity is therefore proposed as a candidate pathway for this group of human genetic diseases. The heads from newly eclosed male Drosophila were used for RNA extraction and profiling on Affymetrix Drosophile Genome 2.0 microarrays. Nine samples were analysed, representing control and experimental lines. Two independent lines of rCAG.rCUG~100 double-stranded RNA were analysed in triplicate. These were compared to 4xUAS control analysed in triplicate. All transgenes were expressed using the elavII-GAL4 pan-neuronal driver. Candidates were selected from the pool of transcripts which showed a 'present' call in all samples. T-tests were performed on raw values to determine samples that showed a significant difference with a P-value < 0.05.
Project description:Perturbation of the Akt/Gsk3-beta signaling pathway is common to Drosophila expressing expanded untranslated CAG, CUG and AUUCU repeat RNAs