Читать книгу Pathology of Genetically Engineered and Other Mutant Mice - Группа авторов - Страница 63

Spontaneous mutations, including sequence variants, copy number variants, small indels, and multigenic chromosomal aberrations constantly arise in colonies but at relatively low rates so they are often missed unless a careful screening program is in place to identify them. This is called genetic drift and can be a major problem for large production colonies. There is also the real potential problem of genetic contamination, where strains are inadvertently mixed. To minimize and control these problems, two approaches are used in large production colonies: the Genetic Stability Program (GSP) (Methods for maintaining genetic stability of inbred animal strains (https://www.jax.org/jax‐mice‐and‐services/find‐and‐order‐jax‐mice/why‐jax‐mice/patented‐genetic‐stability‐program) US 7592501 [22 September 2009]; SG 119769; CN 200480023858.4 [23 June 2010]; AU [11 November 2010]; US 8110721 [7 February 2012]; JP 5072359 [31 August 2012]; USA 8552254 [8 September 2013]) and a genetic quality control program [37]. GSP essentially resets the genetic drift back to an arbitrary start point every ~5 generations by the use of a large pool of inbred embryos to replace the Founder stock. Genetic quality control programs regularly screen breeders at the top and sample the bottom of the production chain for a variety of molecular markers (SNPs) and phenotypes [38]. Newer methods, built around SNPs, utilize MiniMUGA Genotyping Arrays [38]. Prior to polymerase chain reaction (PCR), a variety of diagnostic screens (enzyme assays) and tail skin grafts were used (https://resources.jax.org/misc/jax‐handbook‐genetically‐standardized‐mice).

Spontaneous mutations can be recessive, semi‐dominant, or dominant and can be true nulls, hypomorphic alleles, or gain‐of‐function mutations. Some result from retrovirus integration events, such as the hairless allele (Hr^hr) discussed above [39]. Radiation and chemical mutagenesis are also used to create mutations in mice without targeting specific genes, although specific phenotypes may be the focus. Genetically engineered mice can be created by transgenesis, recombineering, or nuclease mediated approaches. While many engineered mutations are called knockouts, not all are true nulls so this term has to be used carefully.