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Relative gene-silencing efficiencies of small interfering RNAs targeting sense and antisense transcripts from the same genetic locus.

ABSTRACT: Short interfering RNAs (siRNAs) directed against different regions of genes display marked variation in their potency in mediating mRNA degradation. Various factors have been proposed to affect the efficacy of siRNA. We explored some of the factors by evaluating in cultured human cells 28 randomly selected siRNAs targeting the GPR39 and MGC29643 transcripts derived from the same genetic locus but transcribed in opposite directions. Twenty of the 24 siRNAs targeting the overlapping regions of the transcripts simultaneously reduced the levels of both transcripts. Single nucleotide changes in either of the siRNA strands significantly reduced the gene-silencing efficiency of the siRNA on targeted sense transcript without affecting the antisense transcript. Overall, we observed a greater gene-silencing efficiency on the MGC29643 transcript than on the GPR39 transcript in HeLa cells. Since MGC29643 transcript is more abundant than the GPR39 transcript [0.24 versus 0.008% relative to 100% for glyceraldehyde-3-phosphate dehydrogenase (GAPDH)], the results suggest that the abundance of the mRNA affects the efficiency of silencing. Two additional observations supported this hypothesis. First, GAPDH whose intracellular level is the highest of the three was the most efficiently silenced. Second, a reversal of gene-silencing efficiency was observed in U-138 MG cells in which the relative abundance of the GPR39 and MGC29643 transcripts is also reversed. Our study suggests that low-abundant transcripts are less susceptible to siRNA-mediated degradation than medium- and high-abundant transcripts.

SUBMITTER: Hu X

PROVIDER: S-EPMC516062 | biostudies-literature | 2004

REPOSITORIES: biostudies-literature

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Relative gene-silencing efficiencies of small interfering RNAs targeting sense and antisense transcripts from the same genetic locus.

Hu Xiuyuan X Hipolito Sharlene S Lynn Rebecca R Abraham Violet V Ramos Silvester S Wong-Staal Flossie F

Nucleic acids research 20040827 15

Short interfering RNAs (siRNAs) directed against different regions of genes display marked variation in their potency in mediating mRNA degradation. Various factors have been proposed to affect the efficacy of siRNA. We explored some of the factors by evaluating in cultured human cells 28 randomly selected siRNAs targeting the GPR39 and MGC29643 transcripts derived from the same genetic locus but transcribed in opposite directions. Twenty of the 24 siRNAs targeting the overlapping regions of the ...[more]

PMID: 15333693

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Project description:Epigenetic methyl-CpG silencing of the ribosomal RNA (rRNA) genes is thought to down-regulate rRNA synthesis in mammals. In contrast, we now show that CpG methylation in fact positively influences rRNA synthesis and processing. Human HCT116 cells, inactivated for DNMT1 and DNMT3b or treated with aza-dC, lack CpG methylation and reactivate a large fraction of normally silent rRNA genes. Unexpectedly, these cells display reduced rRNA synthesis and processing, and accumulate unprocessed 45S rRNA. Reactivation of the rRNA genes is associated with their cryptic transcription by RNA polymerase II. Ectopic expression of cryptic rRNA gene transcripts recapitulates the defects associated with loss of CpG methylation. The data demonstrate that rRNA gene silencing prevents cryptic RNA polymerase II transcription of these genes. Lack of silencing leads to the partial disruption of rRNA synthesis and rRNA processing, providing an unexpected explanation for the cytotoxic effects of loss of CpG methylation. Agilent custom microarray analyses of transcripts from sense and antisense strands of the human rRNA genes present in total nuclear RNA from HCT116-DNMT1-/-;DNMT3b-/- (DKO) and HCT116 (PS) cells. The DKO/PS RNA ratio was normalized within the 5â region of the 45S ribosomal RNA, since this sense coding region was found by quantitative Northern and S1-mapping analyses to equally present in the RNA pools from both cells (as compared to total RNA levels and 18S and 28S levels). The distribution for sense RNAs from the coding region is strongly influenced by the predominant RPI 45S rRNA transcript and hence peaks at 0, the DKO and PS 45S rRNA signals having been normalized. 60-mer probes were designed to tile Human rDNA (GenBank accession U13369) on both strands using ArrayOligoSelector (Wardle et al., 2006). A total of 1,146 different non-overlapping probes (573 for each DNA strand) were designed to cover the 43 kb of human rDNA and each printed in triplicate on the array. The experiment was performed using a dye-swap duplicate analysis. The microarrays were scanned on a G2565CA DNA microarray scanner (Agilent Technologies) and the quantification performed using the Feature Extraction software (Agilent technologies). The data were analyzed using the LIMMA software package in R (Smyth and Speed, 2003).

Dataset Information

Relative gene-silencing efficiencies of small interfering RNAs targeting sense and antisense transcripts from the same genetic locus.

Publications

Relative gene-silencing efficiencies of small interfering RNAs targeting sense and antisense transcripts from the same genetic locus.

Similar Datasets

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