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Gene knockdown refers to an experimental technique by which the expression of one or more of an organism's genes are reduced. The reduction can occur either through genetic modification or by treatment with a reagent such as a short DNA or RNA oligonucleotide that has a sequence complementary to either gene or an mRNA transcript.[1]

Gene Knockdowns vs. Transient KnockdownsEdit

If genetic modification of DNA is done, the result is called "knockdown organism." If the change in gene expression is caused by an oligonucleotide binding to an mRNA or temporarily binding to a gene, this leads to a temporary change in gene expression that does not modify the chromosomal DNA, and the result is referred to as a "transient knockdown".[1]

In a transient knockdown, the binding of this oligonucleotide to the active gene or its transcripts causes decreased expression through a variety of processes. Binding can occur either through the blocking of transcription (in the case of gene-binding), the degradation of the mRNA transcript (e.g. by small interfering RNA (siRNA) or RNase-H dependent antisense), or through the blocking of either mRNA translation, pre-mRNA splicing sites, or nuclease cleavage sites used for maturation of other functional RNAs, including miRNA (e.g. by Morpholino oligos or other RNase-H independent antisense).[1][2])

The most direct use of transient knockdowns is for learning about a gene that has been sequenced, but has an unknown or incompletely known function. This experimental approach is known as reverse genetics. Researchers draw inferences from how the knockdown differs from individuals in which the gene of interest is operational. Transient knockdowns are often used in developmental biology because oligos can be injected into single-celled zygotes and will be present in the daughter cells of the injected cell through embryonic development.[3]

Gene knockdown by RNAi InterferenceEdit

RNA interference (RNAi) is a means of silencing genes by way of mRNA degradation.[4] Gene knockdown by this method is achieved by introducing small double-stranded interfering RNAs (siRNA) into the cytoplasm. Small interfering RNAs can originate from inside the cell or can be exogenously introduced into the cell. Once introduced into the cell, exogenous siRNAs are processed by the RNA-induced silencing complex (RISC).[5] The siRNA is complementary to the target mRNA to be silenced, and the RISC uses the siRNA as a template for locating the target mRNA. After the RISC localizes to the target mRNA, the RNA is cleaved by a ribonuclease.

RNAi is widely used as a laboratory technique for genetic functional analysis.[6] RNAi in organisms such as C. elegans and Drosophila provides a quick and inexpensive means of investigating gene function. In C. elegans research, the availability of tools such as the Ahringer RNAi Library give laboratories a way of testing many genes in a variety of experimental backgrounds. Insights gained from experimental RNAi use may be useful in identifying potential therapeutic targets, drug development, or other applications.[7]

CommercializationEdit

So far, knockdown organisms with permanent alterations in their DNA have been engineered chiefly for research purposes. Also known simply as knockdowns, these organisms are most commonly used for reverse genetics, especially in species such as mice or rats for which transient knockdown technologies cannot easily be applied.[3][8]

There are several companies that offer commercial services related to gene knockdown treatments. Sirion Biotech is a company that provides “guaranteed” gene knockdowns of nearly 100%.[8] The company also provides its clients with cell lines with built-in reporter genes and next generation cell models with high gene knockdowns.[8] Bio-Synthesis offers stable and inducible gene knockdown services which offer customer a chance to study gene function in a dynamic ways.

ReferencesEdit

  1. 1.0 1.1 1.2 Summerton, J (2007). Morpholino, siRNA, and S-DNA Compared: Impact of Structure and Mechanism of Action on Off-Target Effects and Sequence Specificity. Med Chem. 7 (7): 651–660.
  2. Summerton, J (1999). Morpholino Antisense Oligomers: The Case for an RNase-H Independent Structural Type. Biochimica et Biophysica Acta 1489 (1): 141–58.
  3. 3.0 3.1 Nasevicius, A, Ekker SC (2000). Effective targeted gene 'knockdown' in zebrafish. Nature Genetics 26 (2): 216–20.
  4. Fire, A (1997). Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature 391 (6669): 806-811.
  5. Pratt, AJ (2009). The RNA-induced silencing complex: a versatile gene-silencing machine.. Journal of Biological Chemistry 284: 17897-901.
  6. Fraser, AG (2000). Functional genomic analysis of C. elegans chromosome I by systematic RNA interference.. Nature 408: 325-330.
  7. Aagaard, L (2007). RNAi therapeutics: principles, prospects and challenges.. Advanced Drug Delivery Review 59: 75-86.
  8. 8.0 8.1 8.2
    1. redirect Template:Cite web

See alsoEdit




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