Project description:Transcriptional down regulation caused by intronic triplet repeat expansions underlies diseases such as Friedreich?s ataxia. This down regulation of gene expression is coupled with epigenetic changes but the underlying mechanisms are unknown. Here, we show that an intronic TTC/GAA triplet expansion within the IIL1 gene of Arabidopsis thaliana results in accumulation of 24-nt siRNAs and repressive histone marks at the IIL1 locus, which in turn causes its transcriptional down regulation and an associated phenotype. Knocking down DICER LIKE-3 (DCL3), which produces 24-nt siRNAs, suppressed transcriptional down regulation of IIL1 and the expansion-associated phenotype. Furthermore, knocking down additional components of the RNA-dependent DNA Methylation (RdDM) pathway, also suppressed both transcriptional down regulation of IIL1 and the repeat expansion associated phenotype. Thus our results show that triplet repeat expansions can lead to local siRNA biogenesis, which in turn down regulates transcription through an RdDM-dependent epigenetic modification.
Project description:Development of LNA gapmers, antisense oligonucleotides used for efficient inhibition of target RNA expression, is limited by non-target mediated hepatotoxicity issues. In the present study, we investigated hepatic transcription profiles of mice receiving non-toxic and toxic LNA gapmers after a single and repeat administration.
Project description:Development of LNA gapmers, antisense oligonucleotides used for efficient inhibition of target RNA expression, is limited by non-target mediated hepatotoxicity issues. In the present study, we investigated hepatic transcription profiles of mice receiving non-toxic and toxic LNA gapmers after a single and repeat administration. To understand the mechanism of LNA gapmer-induced heptotoxicity in mice, we investigated the transcription profiles of liver RNA isolated from mice receiving non-toxic sequence (NTS-1), toxic sequence (TS-2), or severely toxic sequence (HTS-3) of LNA gapmers at 25 mg/kg (dose volume of 10 mL/kg) at 8, 16, or 72 hrs after a single administration (by subcutaneous injection ) using microarray analysis. We also investigated the transcription profiles of liver RNA isolated from mice receiving non-toxic sequence (NTS-1) or toxic sequence (TS-2) of LNA gapmers at 25 mg/kg (dose volume of 10 mL/kg) at 2 weeks after repeated administration (by subcutaneous injection ) using microarray analysis.
Project description:Small interfering RNAs (siRNAs) are critical for proper development and immunity in eukaryotes1. Plants produce siRNAs with lengths of 21-, 22-, or 24- nucleotides (nt), wherein the 21- and 24-nt siRNAs mediate mRNA cleavage and DNA methylation2,3, respectively. However, the biological functions of 22-nt siRNAs remain elusive. Here we report the identification and characterization of a group of endogenous 22-nt siRNAs generated from the action of DICER-LIKE 2 (DCL2). When cytoplasmic RNA decay and DCL4 are deficient, the massive accumulation of 22-nt siRNAs causes pleiotropic growth disorders, including severe dwarfism, meristem defect, and pigmentation. Notably, two genes that encode nitrate reductases, NIA1 and NIA2, produce nearly half of the total of 22-nt siRNAs. Production of 22-nt siRNA triggers explosive self-amplification that leads to a small RNA storm, and induces dramatic translational repression both gene-specifically and globally. 22-nt siRNAs are also found to preferentially accumulate upon nitrogen deficiency, which acts to restrain plant growth and promote stress responses. Thus, our research uncovers the unique properties of 22-nt siRNAs, a previously unexplored class of plant siRNAs, and highlights the length of small RNA as a major functional determinant.
Project description:Small interfering RNAs (siRNAs) are critical for proper development and immunity in eukaryotes1. Plants produce siRNAs with lengths of 21-, 22-, or 24- nucleotides (nt), wherein the 21- and 24-nt siRNAs mediate mRNA cleavage and DNA methylation2,3, respectively. However, the biological functions of 22-nt siRNAs remain elusive. Here we report the identification and characterization of a group of endogenous 22-nt siRNAs generated from the action of DICER-LIKE 2 (DCL2). When cytoplasmic RNA decay and DCL4 are deficient, the massive accumulation of 22-nt siRNAs causes pleiotropic growth disorders, including severe dwarfism, meristem defect, and pigmentation. Notably, two genes that encode nitrate reductases, NIA1 and NIA2, produce nearly half of the total of 22-nt siRNAs. Production of 22-nt siRNA triggers explosive self-amplification that leads to a small RNA storm, and induces dramatic translational repression both gene-specifically and globally. 22-nt siRNAs are also found to preferentially accumulate upon nitrogen deficiency, which acts to restrain plant growth and promote stress responses. Thus, our research uncovers the unique properties of 22-nt siRNAs, a previously unexplored class of plant siRNAs, and highlights the length of small RNA as a major functional determinant.
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:Small interfering RNAs (siRNAs), the guides that direct RNA interference (RNAi), provide a powerful tool to reduce the expression of a single gene in human cells. Ideally, dominant, gain-of-function human diseases could be treated using siRNAs that specifically silence the mutant disease allele, while leaving expression of the wild-type allele unperturbed. Previous reports suggest that siRNAs can be designed with single-nucleotide specificity, but no rational basis for the design of siRNAs with single nucleotide discrimination has been proposed. Keywords: siRNA, single-nucleotide discrimination, SOD1, allele-specific