A knockout mouse is a genetically engineered mouse in which one or more
genes have been turned off through a gene knockout. Knockout mice are important animal models for studying the role of genes which have been sequenced, but have unknown functions. By causing a specific gene to be inactive in the mouse, and observing any differences from normal behaviour or condition, researchers can infer its probable function.
Mice are currently the most closely related laboratory animal species to
humans, for which the knockout technique can easily be applied. They are widely used in knockout experiments, especially those investigating genetic questions that relate to human physiology. Gene knockout in rats is much harderFact|date=December 2007 and has only been possible since 2003.
The first knockout mouse was created by
Mario R. Capecchi, Martin Evansand Oliver Smithiesin 1989, for which they were awarded the Nobel Prizefor Medicine in 2007. Aspects of the technology for generating Knockout mice, and the mice themselves have been patented in many countries by private companies.
Knocking out the activity of a gene provides information about what that gene normally does. Humans share many genes with mice. Consequently, observing the characteristics of knockout mice gives researchers information that can be used to better understand how a similar gene may cause or contribute to disease in humans.
Examples of research in which knockout mice have been useful include studying and modeling different kinds of
cancer, obesity, heart disease, diabetes, arthritis, substance abuse, anxiety, agingand Parkinson's disease. Knockout mice also offer a biological and scientific context in which drugs and other therapies can be developed and tested.
Millions of knockout mice are used in experiments each year. [ [http://www.genome.gov/10005834 genome.gov | Background on Mouse as a Model Organism ] ]
There are several thousand different strains of knockout mice. [ [http://www.genome.gov/10005834 genome.gov | Background on Mouse as a Model Organism ] ] Many of mouse models are named after the gene that has been inactivated. For example, the
p53knockout mouse is named after the p53 gene which codes for a protein that normally suppresses the growth of tumors by arresting cell division. Humans born with mutations that inactivate the p53 gene suffer from Li-Fraumeni syndrome, a condition that dramatically increases the risk of developing bone cancers, breast cancerand blood cancers at an early age. Other mouse models are named, often with creative flair, according to their physical characteristics or behaviors.
There are several variations to the procedure of producing knockout mice; the following is a typical example.
#The gene to be knocked out is isolated from a mouse gene library. Then a new
DNA sequenceis engineered which is very similar to the original gene and its immediate neighbor sequence, except that it is changed sufficiently to make it inoperable. Usually, the new sequence is also given a marker gene, a gene that normal mice don't have and that confers resistance to a certain toxic agent or that produces an observable change (e.g. colour or fluorescence). The chances of a successful recombination event are relatively low, so the majority of altered cells will have the gene changed for only one of the two relevant chromosomes - they are said to be heterozygous.
#From a mouse
blastocyst(a very young embryoconsisting of a ball of undifferentiated cells with surrounding extraembryonic cells), stem cells are isolated; these can be grown " in vitro". For this example, we will take a stem cell from a white mouse.
#The stem cells from step 2 are combined with the new sequence from step 1. This is done via
electroporation(using electricity to transfer the DNA across the cell membrane). Some of the electroporated stem cells will incorporate the new sequence into their chromosomes in place of the old gene; this is called homologous recombination. The reason for this process is that the new and the old sequence are very similar. Using the marker gene from step 1, those stem cells that actually did incorporate the new sequence can be quickly isolated from those that did not.
#The stem cells from step 3 are inserted into a mouse
blastocyst. For this example, we use blastocysts from a grey mouse. These blastocysts are then implanted into the uterusof female mice, to complete the pregnancy. The blastocysts contain two types of stem cells: the original ones (grey mouse), and the newly engineered ones (white mouse). The newborn mice will therefore be chimeras: parts of their bodies result from the original stem cells, other parts result from the engineered stem cells. Their furs will show patches of white and grey.
#Newborn mice are only useful if the newly engineered sequence was incorporated into the
germ cells (egg or sperm cells). These new mice are crossed with others of the white type for offspring that are all white. These mice still contain one functional copy of the gene and must be further inbred to produce mice that carry no functional copy of the original gene (i.e. are homozygousfor that allele).
A detailed explanation of how knockout (KO) mice are created is located at the website of The
Nobel Prize in Physiology or Medicine2007 [ [http://nobelprize.org/nobel_prizes/medicine/laureates/2007/adv.html The Nobel Prize in Physiology or Medicine 2007] ] .
While knockout mice technology represents a valuable research tool, some important limitations exist. About 15 percent of gene knockouts are developmentally lethal, which means that the genetically altered embryos cannot grow into adult mice. This problem is often overcome through the use of
conditional mutations. The lack of adult mice limits studies to embryonic development and often makes it more difficult to determine a gene's function in relation to human health. In some instances, the gene may serve a different function in adults than in developing embryos.
Knocking out a gene also may fail to produce an observable change in a mouse or may even produce different characteristics from those observed in humans in which the same gene is inactivated. For example, mutations in the p53 gene are associated with more than half of human cancers and often lead to tumors in a particular set of tissues. However, when the p53 gene is knocked out in mice, the animals develop tumors in a different array of tissues.
There is variability in the whole procedure depending largely on the strain from which the stem cells have been derived. Generally cells derived from strain 129 are used. This specific strain is not suitable for many experiments (e.g., behavioral), so it is very common to
backcrossthe offspring to other strains. Some genomic loci have been proven very difficult to knock out. Reasons might be the presence of repetitive sequences, extensive DNA methylation, or heterochromatin.
Mus musculus(house mouse)
* [http://www.scq.ubc.ca/?p=264 Studying Gene Function: Creating Knockout Mice] - a review from the Science Creative Quarterly
* [http://www.knockoutmouse.org The Knock Out Mouse Project (KOMP) Data Coordination website] - The public interface for information on the status of the genes included in the KOMP initiative.
* [http://www.komp.org The Knock Out Mouse Project (KOMP) Repository website] - The web site for ordering ES cells, vectors, and mice generated by the KOMP project
* [http://www.informatics.jax.org Mouse Genome Informatics (MGI) website] - community model organism database for the laboratory mouse
Wikimedia Foundation. 2010.
Look at other dictionaries:
knockout mouse — Transgenic mouse in which a particular gene has been deleted. Often shows disappointingly little phenotypic change usually because there are alternative mechanisms or because the right challenge is not being made (some genes are probably… … Dictionary of molecular biology
knockout mouse — a mouse that has had a specific gene artificially deleted from its genome … Medical dictionary
knockout mouse — noun Any of several forms of mice that have been genetically engineered by inactivating specific genes … Wiktionary
knockout mouse — … Useful english dictionary
International Knockout Mouse Consortium — IKMC: International Knockout Mouse Consortium Content Description International Knockout Mouse Consortium Organism(s) Mice … Wikipedia
Knockout rats — Knockout rats=A knockout rat is a rat with a single gene disruption used for academic and pharmaceutical research. Knockout rats can mimic human diseases and are important tools for studying gene function (functional genomics) and for drug… … Wikipedia
Mouse — Mice redirects here. For other uses, see Mice (disambiguation). This article is about the animal. For the computer input device, see Mouse (computing). For other uses, see Mouse (disambiguation). Mouse Temporal range: Late Miocene–Recent … Wikipedia
Knockout de genes — Saltar a navegación, búsqueda Un knockout de un gen ( gen knock out) es una técnica genética que consiste en bloquear la expresión de un gen específico en un organismo (un ratón, una planta, una levadura...), sustituyendo el gen original en su… … Wikipedia Español
Mouse models of colorectal and intestinal cancer — Mouse models of colorectal cancer and intestinal cancer are experimental systems in which mice are genetically manipulated or challenged with chemicals to develop malignancies in the gastrointestinal tract. These models enable researchers to… … Wikipedia
mouse — A small rodent belonging to the genus Mus. joint mice Small fibrous, cartilaginous, or bony loose bodies in the synovial cavity of a joint. knockout m. a m. from whose genome a single gene has been artificially deleted.Experimental animals… … Medical dictionary