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Genome engineering refers to the strategies and techniques developed in recent years for the targeted, specific modification of the genetic information – or genome – of living organisms. It represents a very active field of research because of the wide range of possible applications, particularly in the areas of human health - the correction of a gene carrying a harmful mutation, the production of therapeutic proteins, the elimination of persistent viral sequences - agricultural biotechnology - the development of new generations of genetically modified plants - and for the development of research tools - for example, to explore the function of a gene. Early technologies developed to insert a gene into a living cell, such as transgenesis, are limited by the random nature of the insertion of the new sequence into the genome. The new gene is positioned blindly, and may inactivate or disturb the functioning of other genes or even cause severe unwanted effects; it may trigger a process of cancerization, for example. Furthermore, these technologies offer no degree of reproducibility, as there is no guarantee that the new sequence will be inserted at the same place in two different cells. The major advantage of genome engineering, which uses more recent knowledge and technology, is that it enables a specific area of the DNA to be modified, thereby increasing the precision of the correction or insertion, preventing any cell toxicity and offering perfect reproducibility. Genome engineering and synthetic genomics (designing artificial genomes) are currently among the most promising technologies in terms of applied biological research and industrial innovation. == General principles == Early approaches to genome engineering involved modifying genetic sequences using only homologous recombination. Using a homologous sequence located on another strand as a model can lead this natural DNA maintenance mechanism to repair a DNA strand. It is possible to induce homologous recombinations between a cellular DNA strand and an exogenous DNA strand inserted in the cell by researchers, using a vector such as the modified genome of a retrovirus. The recombination phenomenon is flexible enough for a certain level of change (addition, suppression or modification of a DNA portion) to be introduced to the targeted homologous area. In the 1980s, Mario R. Capecchi and Oliver Smithies worked on the homologous recombination of DNA as a “gene targeting” tool; in other words, as an instrument for the inactivation or modification of specific genes. Working with Martin J. Evans, they developed a process for the modification of the mouse genome by modifying the DNA of mouse embryonic stem cells in culture and injecting these modified stem cells into mouse embryos. Genetically modified mice generated using this method make useful laboratory models to study human diseases. This tool is now commonly used in medical research. The three researchers were awarded the 2007 Nobel Prize in Medicine for their work.〔(The Nobel Prize in Physiology or Medicine 2007 )〕 Modifying genomes using only homologous recombination remained a long and random process, until additional developments were made that could increase the rate of homologous recombination in somatic cell types. These developments include two mechanistically distinct methods of triggering the cells inherent DNA repair mechanisms which are required to insert a foreign gene sequence into a live cell. The first method is by site directed endonucleases (restriction enzymes), which include specific technologies such as zinc finger nucleases (ZFNs) and meganucleases. Site directed endonucleases achieve gene modification through causing double stranded DNA (dsDNA) breaks which triggers the cells natural DNA repair mechanism, predominantly non homologous end joining (NHEJ) as well as a low frequency of homologous recombination (HR). The second method is recombinant adeno-associated virus (rAAV) mediated genome engineering which induces high frequencies of homologous recombination alone, thus forgoing the need to perform dsDNA breaks. Methods in genome engineering: * Insertion involves introducing a gene into a chromosome to obtain a new function (for example to obtain a better drought-resistant plant) or to compensate for a defective gene, particularly by making it possible to manufacture a functional protein if the protein produced by the patient is defective (such as factor VIII in hemophilia A). * Inactivation, or “knock-out”, is today mainly used in fundamental research to shed light on the function of a gene by observing the anomalies that occur as a result of its inactivation. It can also have other applications, for example to remove a persistent viral sequence from infected cells, or in agriculture to eliminate the irritant or allergenic properties of a plant. * Correction aims to remove and replace a defective gene sequence with a functional sequence. This correction can be performed on a very short sequence, sometimes just a few nucleotides, such as in the case of drepanocytosis (sickle cell anemia). In plants, this manipulation can also help improve the properties of a species without the addition of foreign DNA. 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 engineering」の詳細全文を読む スポンサード リンク
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