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Perturbation of the Akt/Gsk3-beta signaling pathway is common to Drosophila expressing expanded untranslated CAG, CUG and AUUCU repeat RNAs

ABSTRACT: Recent evidence supports a role for RNA as a common pathogenic agent in both the “polyglutamine” and “untranslated” dominant expanded repeat disorders. One feature of all repeat sequences currently associated with disease is their predicted ability to form a hairpin secondary structure at the RNA level. In order to investigate mechanisms by which hairpin forming repeat RNAs could induce neurodegeneration, we have looked for alterations in gene transcripts as hallmarks of the cellular response to toxic hairpin repeat RNAs. Three disease associated repeat sequences - CAG, CUG and AUUCU - were specifically expressed in the neurons of Drosophila and resultant common, early, transcriptional changes assessed by microarray analyses. Transcripts that encode several components of the Akt/Gsk3-β signalling pathway were altered as a consequence of expression of these repeat RNAs, indicating that this pathway is a component of the neuronal response to these pathogenic RNAs and may represent an important common therapeutic target in this class of diseases.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE27178 | GEO | 2011/04/28

SECONDARY ACCESSION(S): PRJNA137367

REPOSITORIES: GEO

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Project description:Recent evidence supports a role for RNA as a common pathogenic agent in both the “polyglutamine” and “untranslated” dominant expanded repeat disorders. One feature of all repeat sequences currently associated with disease is their predicted ability to form a hairpin secondary structure at the RNA level. In order to investigate mechanisms by which hairpin forming repeat RNAs could induce neurodegeneration, we have looked for alterations in gene transcripts as hallmarks of the cellular response to toxic hairpin repeat RNAs. Three disease associated repeat sequences - CAG, CUG and AUUCU - were specifically expressed in the neurons of Drosophila and resultant common, early, transcriptional changes assessed by microarray analyses. Transcripts that encode several components of the Akt/Gsk3-β signalling pathway were altered as a consequence of expression of these repeat RNAs, indicating that this pathway is a component of the neuronal response to these pathogenic RNAs and may represent an important common therapeutic target in this class of diseases. The heads from newly eclosed Male Drosophila were used for RNA extraction and profiling on Affymetrix Drosophile Genome 2.0 microarrays. Twenty samples were analysed, representing control and experimental lines. Two independently derived control lines were used in each exeriment, totaling 4 samples. The tri-nucleotide repeats (CAG, CUG, CAA) were represented by three independently derived two transgene insertion lines each in one experiment and two independent four transgene insertion lines each in a second experiment, totaling 15 samples. A single four transgene insertion line was analysed for AUUCU. Candidates were selected from the pool of transcripts which showed a ‘present’ call in either all independent lines for a particular repeat sequence, or in all samples for the elav- GAL4/+ control in that experiment. Where possible, T-tests were performed on raw values to determine samples that showed a significant difference with a P-value < 0.05.

Project description:In plants, RNA polymerase II (Pol II) transcription of inverted DNA repeats produces hairpin RNAs that are processed by several DICER-LIKE enzymes into siRNAs that are 21-24-nt in length. When targeted to transcriptional regulatory regions, the 24-nt size class can induce RNA-directed DNA methylation (RdDM) and transcriptional gene silencing (TGS). In a forward genetic screen to identify mutants defective in RdDM of a target enhancer leading to TGS of a downstream GFP reporter gene in Arabidopsis thaliana, we recovered a structurally mutated silencer locus, named SM-NM-^T35S, in which the 35S promoter driving transcription of an inverted repeat of target enhancer sequences had been specifically deleted. Although Pol II-dependent, hairpin-derived 21-24-nt siRNAs were no longer generated at the newly created SM-NM-^T35S locus, the GFP reporter gene was nevertheless still partially silenced. Silencing was associated with methylation in a short tandem repeat in the upstream target enhancer and with low levels of 24-nt tandem repeat siRNAs. Introducing an nrpd1 mutation into the SM-NM-^T35S line fully released GFP silencing and eliminated both the tandem repeat methylation and associated 24-nt siRNAs, demonstrating their dependence on Pol IV. Deletion of the 35S promoter thus revealed a Pol IV-dependent pathway of 24-nt siRNA biogenesis that was previously inhibited or masked by the Pol II-dependent pathway in wild-type plants. Both Pol II- and Pol IV-dependent siRNAs accrued predominantly from cytosine (C)-containing segments of the tandem repeat monomer, suggesting that the local base composition influenced siRNA accumulation. Preferential accumulation of siRNAs at C-containing sequences was also observed at an endogenous tandem repeat comprising discrete C-rich and AT-rich sections. Our studies illuminate the potential complexity of siRNA generation at repeat-containing loci and show that Pol IV can act in siRNA biogenesis in the absence of a conventional Pol II promoter. Examination of whole-genome DNA methylation status in transgenic T+S Arabidopsis plant

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Perturbation of the Akt/Gsk3-beta signaling pathway is common to Drosophila expressing expanded untranslated CAG, CUG and AUUCU repeat RNAs

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