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RNA-Induced Silencing Complex: A multicomponent, ribonucleoprotein complex comprised of one of the family of Argonaute proteins and the "guide strand" of the one of the 20- to 30-nucleotide small RNAs. Risc cleaves specific RNAs, which are targeted for degradation by homology to these small RNAs. Functions in regulating gene expression are determined by the specific argonaute protein and small RNA including siRNA (RNA, Small interfering), miRNA (Microrna), or piRNA (Piwi-interacting rna).

RNA Interference

JoVE 10804

RNA interference (RNAi) is a process in which a small non-coding RNA molecule blocks the expression of a gene by binding to its messenger RNA (mRNA) transcript, preventing the protein from being translated.

This process occurs naturally in cells, often through the activity of microRNAs. Researchers can take advantage of this mechanism by introducing synthetic RNAs to selectively deactivate specific genes for research or therapeutic purposes. For example, RNAi could be used to suppress genes that are overactive in diseases such as cancer. First, double-stranded RNA with a sequence complementary to the targeted gene is synthesized. Different types of double-stranded RNA can be used, including short interfering RNA (siRNA) and small hairpin RNA (shRNA). shRNA is one strand of RNA that is folded over—creating a double-stranded RNA with a hairpin loop on one side—and is a precursor of siRNA. The double-stranded RNA is then introduced into cells by methods such as injection or delivery by vectors, such as modified viruses. If shRNA is used, RNase enzymes in the cell, such as Dicer, cleave it down to the shorter siRNA, removing the hairpin loop. The siRNA then binds to an enzyme called Argonaute, which is part of a complex called RISC (RNA-induced silencing complex). Here, the two strands of the siRNA separate. One floats away w

 Core: Gene Expression

MicroRNAs

JoVE 10801

MicroRNA (miRNA) are short, regulatory RNA transcribed from introns—non-coding regions of a gene—or intergenic regions—stretches of DNA present between genes. Several processing steps are required to form biologically active, mature miRNA. The initial transcript, called primary miRNA (pri-mRNA), base-pairs with itself forming a stem-loop structure. Within the nucleus, an endonuclease enzyme, called Drosha, shortens the stem-loop structure into hairpin-shaped pre-miRNA. After the pre-miRNA ends have been methylated to prevent degradation, it is exported from the nucleus into the cytoplasm. In the cytoplasm, another endonuclease enzyme, called Dicer, cuts the pre-miRNA into a 21-24 nucleotide-long miRNA duplex. Then, Dicer cleaves one strand of the duplex, releasing a single strand of mature miRNA. The mature miRNA is loaded into a protein complex called RNA-induced silencing complex (RISC), which the miRNA then guides to the complementary region of its target mRNA. The extent of complementary base-pairing between miRNA and 3’ untranslated region of target mRNA determines the gene silencing mechanism. Extensive or near-perfect complementarity causes degradation of mRNA, whereas limited base-pairing inhibits translation. While silencing via mRNA degradation is irreversible, translation inhibition is reversible since stable mRNA can

 Core: Gene Expression

RNAi in C. elegans

JoVE 5105

RNA interference (RNAi) is a widely used technique in which double stranded RNA is exogenously introduced into an organism, causing knockdown of a target gene. In the nematode, C. elegans, RNAi is particularly easy and effective because it can be delivered simply by feeding the worms bacteria that express double stranded RNA (dsRNA) that is complementary to a gene of interest. First,…

 Biology I

A Bioinformatics Pipeline to Accurately and Efficiently Analyze the MicroRNA Transcriptomes in Plants

1Beijing Key Laboratory of Agricultural Genetic Resources and Biotechnology, Beijing Agro-biotechnology Research Center, Beijing Academy of Agriculture and Forestry Sciences, 2State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, School of Advanced Agricultural Sciences and School of Life Sciences, Peking University

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JoVE 59864

 JoVE In-Press
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