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Transfection of microRNA Mimics Should Be Used with Caution.

ABSTRACT: Transient transfection of chemically synthesized microRNA (miRNA) mimics is being used extensively to study the functions and mechanisms of endogenous miRNAs. However, it remains unclear whether transfected miRNAs behave similarly to endogenous miRNAs. Here we show that transient transfection of miRNA mimics into HeLa cells by a commonly used method led to the accumulation of high molecular weight RNA species and a few hundred fold increase in mature miRNA levels. In contrast, expression of the same miRNAs through lentiviral infection or plasmid transfection of HeLa cells, transgenic expression in primary lymphocytes, and endogenous overexpression in lymphoma and leukemia cell lines did not lead to the appearance of high molecular weight RNA species. The increase of mature miRNA levels in these cells was below 10-fold, which was sufficient to suppress target gene expression and to drive lymphoma development in mice. Moreover, transient transfection of miRNA mimics at high concentrations caused non-specific alterations in gene expression, while at low concentrations achieved expression levels comparable to other methods but failed to efficiently suppress target gene expression. Small RNA deep sequencing analysis revealed that the guide strands of miRNA mimics were frequently mutated, while unnatural passenger strands of some miRNA mimics accumulated to high levels. The high molecular weight RNA species were a heterogeneous mixture of several classes of RNA species generated by concatemerization, 5'- and 3'-end tailing of miRNA mimics. We speculate that the supraphysiological levels of mature miRNAs and these artifactual RNA species led to non-specific changes in gene expression. Our results have important implications for the design and interpretation of experiments primarily employing transient transfection of miRNA mimics.

SUBMITTER: Jin HY

PROVIDER: S-EPMC4667072 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Transfection of microRNA Mimics Should Be Used with Caution.

Jin Hyun Yong HY Gonzalez-Martin Alicia A Miletic Ana V AV Lai Maoyi M Knight Sarah S Sabouri-Ghomi Mohsen M Head Steven R SR Macauley Matthew S MS Rickert Robert C RC Xiao Changchun C

Frontiers in genetics 20151202

Transient transfection of chemically synthesized microRNA (miRNA) mimics is being used extensively to study the functions and mechanisms of endogenous miRNAs. However, it remains unclear whether transfected miRNAs behave similarly to endogenous miRNAs. Here we show that transient transfection of miRNA mimics into HeLa cells by a commonly used method led to the accumulation of high molecular weight RNA species and a few hundred fold increase in mature miRNA levels. In contrast, expression of the ...[more]

PMID: 26697058

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Project description:We investigated functions of miRNAs at the level of the whole transcriptome of primary neurons. We transfected mouse E17.5 forebrain primary neuronal cultures (at four to six days of in vitro development) with miRNA mimics and inhibitors. After approximately 48 h post transfection we profiled the effect of these transfections on gene expression with Illumina mRNA microarrays. Cultures were transfected with mimics and inhibitors of five mouse miRNAs (mmu-miR-124, mmu-miR-434-3p, mmu-miR-143, mmu-miR-145 and mmu-miR-25) and with a mimic of a non-mouse miRNA (cel-miR-67). Direct widespread inhibition of gene expression by the perturbed miRNAs was evident when gene expression in cultures transfected with miRNA mimics was compared to those transfected with the inhibitors (or to matched mock transfected cultures): 3-prime UTRs of downregulated transcripts were significantly enriched in seed matching sites for the perturbed miRNAs. Interestingly, analysis of differential gene expression in mock transfected cells (identified through comparison of mock transfected cultures with matched untreated cultures) revealed that genes inhibited by miRNAs were enriched in genes upregulated in mock transfected cultures. This inhibition was the most efficient by the two neuronal miRNAs under investigation (mmu-miR-124 and mmu-miR-434-3p). To investigate if miRNA mediated inhibition of stress induced genes (i.e. stress associated with transfections) was also the case in other stresses, we profiled gene expression changes triggered by chronic neuronal depolarisation. For this, we treated the cultures with KCl (15 mM, 48 h) and compared them to matched untreated cultures. We found that genes upregulated by KCl had a significant intersection with those upregulated by the mock transfection. Moreover, we also found that genes upregulated by KCl had a significant intersection with genes inhibited by mmu-miR-124 and mmu-miR-434-3p. Therefore we concluded that neuronal miRNAs stabilise the neuronal transcriptome by inhibiting stress inducible genes.

Project description:MicroRNAs (miRNAs) are short noncoding ribonucleic acids known to affect gene expression at the translational level and there is mounting evidence that miRNAs play a role in the function of tumor-associated macrophages (TAMs). To aid the functional analyses of miRNAs in an in-vitro model of TAMs known as M2 macrophages, a transfection method to introduce artificial miRNA constructs or miRNA molecules into primary human monocytes is needed. Unlike differentiated macrophages or dendritic cells, undifferentiated primary human monocytes have been known to show resistance to lentiviral transduction. To circumvent this challenge, other techniques such as electroporation and chemical transfection have been used in other applications to deliver small gene constructs into human monocytes. To date, no studies have compared these two methods objectively to evaluate their suitability in the miRNA functional analysis of M2 macrophages. Of the methods tested, the electroporation of miRNA-construct containing plasmids and the chemical transfection of miRNA precursor molecules are the most efficient approaches. The use of a silencer siRNA labeling kit (Ambion) to conjugate Cy 3 fluorescence dyes to the precursor molecules allowed the isolation of successfully transfected cells with fluorescence-activated cell sorting. The chemical transfection of these dye-conjugated miRNA precursors yield an efficiency of 37.5 ± 0.6% and a cell viability of 74 ± 1%. RNA purified from the isolated cells demonstrated good quality, and was fit for subsequent mRNA expression qPCR analysis. While electroporation of plasmids containing miRNA constructs yield transfection efficiencies comparable to chemical transfection of miRNA precursors, these electroporated primary monocytes seemed to have lost their potential for differentiation. Among the most common methods of transfection, the chemical transfection of dye-conjugated miRNA precursors was determined to be the best-suited approach for the functional analysis of M2 macrophages.

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Transfection of microRNA Mimics Should Be Used with Caution.

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Transfection of microRNA Mimics Should Be Used with Caution.

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