Sources:
http://www.genome.gov/12514551 Date visited: 1-18-13
Drawbacks:
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.
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.
Despite these drawbacks, knockout mice offer one of the most powerful means now available for studying gene function in a
living animal. Such studies will accelerate efforts to translate newfound knowledge of the human and mouse genomes into
better strategies for diagnosing, treating and preventing human disease.
http://www.nih.gov/science/models/mouse/knockout/ Date Visited: 1-18-13
Utility of Knockout Mice
Through research utilizing the mouse as a model for human disease, investigators can translate basic biological
phenomena into a human health perspective. For example, mouse models have added to our understanding of human
obesity, cancer, cardiovascular disease, diabetes, Parkinson's and Alzheimer's, to name just a few. The value of the mouse as a
model organism is derived from the fact that the mouse has similar developmental, physiological, biochemical, and behavioral
patterns to humans. It is worth noting that the similarities between human and mouse are supported at the genotypic level 99% of mouse genes have homologs in humans. Because of the suite of available molecular tools, specifically the long history
of making and studying mouse mutants, along with the genomic and phenotypic similarities with humans, advances in mouse
genetics continue to be a driving force in a broad range of biomedical research activities.
http://medical-dictionary.thefreedictionary.com/Knockout+mice Date visited: 1-18-13
Definition of Knockout Mice
A genetically engineered mouse created by gene targeting—targeted gene disruption—in which a specific gene is deleted or
inactivated by homologous recombination, to study the effects of its absence. Knockout mouse models of human disease have
been created for atherosclerosis, cancer, cystic fibrosis, etc.
http://jcb.rupress.org/content/140/6/1441.full.pdf Date Visited: 1-18-13
Example of Keratin 8 Knockout Mice Strain
This surprising result was confirmed by
K8 knockout mice, which can reach adulthood (Baribault
et al., 1993, 1994), depending on the genetic background.
In one strain, these mice died around day 12 from yet unknown
tissue damage. In a different strain, they survived
to adulthood suffering from colorectal hyperplasia and inflammation.
The overall architecture of K8-expressing
mouse epithelia was established and maintained in all
strains tested in the absence of keratin IF (Baribault et al.,
1994).
Info Packet:
How they are made
Embryotic Stem cells are harvested from mice four days after fertilization. Stem cells can be used ten years after being
harvested
Two Methods:
Gene Targeting or Homologous Recombination
“Researchers specifically manipulate a gene in the ES cell's nucleus.
They introduce an artificial piece of DNA that shares identical, or homologous, sequence to the gene. This
homologous sequence flanks the existing gene's DNA sequence both upstream and downstream of the gene's location
on the chromosome. The cell's own nuclear machinery automatically recognizes the identical stretches of sequence and
swaps out the existing gene or portion of a gene with the artificial piece of DNA. Because the artificial DNA is
inactive, bearing only a genetic tag, or “reporter gene”, designed for use in tracking, the swap eliminates, or “knocks
out,” the function of the existing gene.”
Gene Trapping
“Researchers again manipulate a gene in ES cells. However, instead of directly targeting a gene of interest, a random
process is used. A piece of artificial DNA, containing a reporter gene, is designed to insert randomly into any gene.
The inserted piece of DNA prevents the cell's RNA “splicing” machinery from working properly, thus preventing the
existing gene from producing its designed protein and knocking out its function. As in the first strategy, researchers
can tract the activity of the artificial reporter gene to figure out the existing gene's normal pattern of activity in mouse
tissues.
The resulting mouse pups have some tissues in which a gene has been knocked out – those derived from the altered ES cells.
However, they also have some normal tissues derived from the non-altered embryos into which the altered ES cells were
injected. Consequently, they are not complete knockout mice. It is necessary to crossbreed such mice to produce lines of mice
in which both copies of the gene (one on each chromosome) are knocked out in all tissues. Researchers refer to such mice as
homozygous knockouts.
http://www.cff.org/aboutCFFoundation/Publications/connections/archive/March2010/Targeting-Mutations-that-Cause-CysticFibrosis.cfm Date visited: 1-24-13
http://www.eyeondna.com/2007/10/08/2007-nobel-prize-in-medicine-goes-to-mice-geneticists/ Date Visited 1-24-13
The 2007 Nobel Prize in Physiology or Medicine goes to Mario R. Capecchi, Martin J. Evans, and Oliver Smithies for
their discoveries of principles for introducing specific gene modifications in mice by the use of embryonic stem cells.
http://www.nobelprize.org/nobel_prizes/medicine/laureates/