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DNA fragmentation is the separation or breaking of DNA strands into pieces. It can be done intentionally by laboratory personnel or by cells, or can occur spontaneously. Spontaneous or accidental DNA fragmentation is fragmentation that gradually accumulates in a cell. It can be measured by e.g. the Comet assay. The degree of DNA fragmentation can predict outcomes for in vitro fertilization (IVF) and its expansion intracytoplasmic sperm injection〔 (ICSI). The sperm chromatin dispersion test (SCD) and TUNEL assay are both effective in detecting sperm DNA damage. Using bright-field microscopy, the SCD test appears to be more sensitive than the TUNEL assay.〔 Its main units of measurement is the DNA Fragmentation Index (DFI). A DFI of 20% or more significantly reduces the success rates after ICSI.〔 DNA fragmentation was first documented by Williamson in 1970 when he observed discrete oligomeric fragments occurring during cell death in primary neonatal liver cultures. He described the cytoplasmic DNA isolated from mouse liver cells after culture as characterized by DNA fragments with a molecular weight consisting of multiples of 135 kDa. This finding was consistent with the hypothesis that these DNA fragments were a specific degradation product of nuclear DNA. ==Intentional== DNA fragmentation is often necessary prior to library construction or subcloning for DNA sequences. A variety of methods involving the mechanical breakage of DNA have been employed where DNA is fragmented by laboratory personnel. Such methods include sonication, needle shear, nebulisation, point-sink shearing and passage through a pressure cell. * Restriction digest is the intentional laboratory breaking of DNA strands. It is an enzyme-based treatment used in biotechnology to cut DNA into smaller strands in order to study fragment length differences among individuals or for gene cloning. This method fragments DNA either by the simultaneous cleavage of both strands, or by generation of nicks on each strand of dsDNA to produce dsDNA breaks.〔(【引用サイトリンク】url=https://www.neb.com/applications/library-preparation-for-next-generation-sequencing/dna-fragmentation )〕 * Acoustic shearing of the transmission of high-frequency acoustic energy waves delivered to a DNA library. The transducer is bowl shaped so that the waves converge at the target of interest.〔 * Nebulization forces DNA through a small hole in a nebulizer unit, which results in the formation of a fine mist that is collected. Fragment size is determined by the pressure of the gas used to push the DNA through the nebulizer, the speed at which the DNA solution passes through the hole, the viscosity of the solution, and the temperature.〔 * Sonication, a type of hydrodynamic shearing, subjects DNA to Hydrodynamic shearing by exposure to brief periods of sonication, usually resulting in 700bp fragments. * Point-sink shearing, a type of hydrodynamic shearing, uses a syringe pump to create hydrodynamic shear forces by pushing a DNA library through a small abrupt contraction. About 90% of fragment lengths fall within a two-fold range.〔 * Needle shearing creates shearing forces by passing DNA libraries through small gauge needle.〔 The DNA pass through a gauge needle several times to physically tear the DNA into fine pieces. * French pressure cells pass DNA through a narrow valve under high pressure to create high shearing forces.〔 With a French press, the shear force can be carefully modulated by adjusting the piston pressure. The Press provides a single pass through the point of maximum shear force, limiting damage to delicate biological structures due to repeated shear, as occurs in other disruption methods. * In transposome mediated fragmentation (tagmentation) transposomes are prepared with DNA that is aftwerwords cut so that the transposition events result in fragmented DNA with adapters (instead of an insertion). The relative concentration of transposomes and DNA must be appropriate. 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「DNA fragmentation」の詳細全文を読む スポンサード リンク
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