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Genome editing, or genome editing with engineered nucleases (GEEN) is a type of genetic engineering in which DNA is inserted, replaced, or removed from a genome using artificially engineered nucleases, or "molecular scissors". The nucleases create specific double-strand breaks (DSBs) at desired locations in the genome, and harness the cell’s endogenous mechanisms to repair the induced break by natural processes of homologous recombination (HR) and nonhomologous end-joining (NHEJ). There are currently four families of engineered nucleases being used: Zinc finger nucleases (ZFNs), Transcription Activator-Like Effector Nucleases (TALENs), the CRISPR/Cas system, and engineered meganuclease re-engineered homing endonucleases. It is commonly practiced in genetic analysis that in order to understand the function of a gene or a protein function one interferes with it in a sequence-specific way and monitors its effects on the organism. However, in some organisms it is difficult or impossible to perform site-specific mutagenesis, and therefore more indirect methods have to be used, such as silencing the gene of interest by short RNA interference (siRNA) .〔''Fire, A. et al., Potent and specific genetic interference by double-stranded RNA in ''Caenorhabditis elegans''" ''Nature'' 391 (6669), 806-811 (1998).''〕 Yet gene disruption by siRNA can be variable and incomplete. Genome editing with nucleases such as ZFN is different from siRNA in that the engineered nuclease is able to modify DNA-binding specificity and therefore can in principle cut any targeted position in the genome, and introduce modification of the endogenous sequences for genes that are impossible to specifically target by conventional RNAi. Furthermore, the specificity of ZFNs and TALENs are enhanced as two ZFNs are required in the recognition of their portion of the target and subsequently direct to the neighboring sequences. It was chosen by Nature Methods as the 2011 Method of the Year.〔''Method of the Year 2011. Nat Meth 9 (1), 1-1.''〕 == Concept == A common approach in the modern biological research is to manipulate the genetic sequence (genotype) of an organism (or a single cell) and observe the impact of this change on the organism (phenotype). Such approach is called reverse genetics and its significance for the modern biology lies in its relative simplicity. In contrast, in forward genetics a new phenotype is first observed and then its genetic basis is studied. This course is more complex, since phenotypic changes are often a result of multiple genetic interactions. Among the key aspects of reverse genetic analysis is the ability to modify the genetic code. This can be achieved by: * site-directed mutagenesis which employs polymerase chain reaction (PCR) with primers containing the desired mutation. ''(In which organisms is it used? Just bacteria?)'' * recombination based methods that utilize the natural ability of cells to exchange DNA between its own genetic information and an exogenous DNA. These methods have been made possible in yeast and mice. Both approaches have several drawbacks: * They are less successful in other organisms. * They also require stringent selection steps and thus addition of selection specific sequences, along with those incorporated into the DNA. * They can be quite inefficient - e.g. in mouse embryonic stem cells treated with donor DNA, in only 1 of a million the DNA got incorporated at the desired position.〔''Capecchi, M., Altering the genome by homologous recombination" ''Science'' 244 (4910), 1288-1292 (1989).''〕 Use of other techniques such as P-element transgenesis in Drosophila also have their limitations, the major one being the randomness of incorporation and the possibility of affecting other genes and expression patterns. Hence, genomic editing with engineered nucleases, a rapidly growing technology is a promising new approach. It overcomes these shortcomings and uses relatively simple concepts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Genome editing」の詳細全文を読む スポンサード リンク
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