What is a knockout animal?
So-called knockout animals are animals that lack the target gene, obtained by disrupting a specific gene.
The technology for creating knockout animals is triggered by the discovery of embryonic stem cells (ES cells) that have totipotency (the ability to differentiate into all cells; that is, the ability to create whole individuals). The low rate of target gene disruption by homologous recombination of exogenous DNA and genome is practically impossible to introduce by the conventional gene manipulation with pronuclear stage embryos. However, it can be introduced by using ES cells that can be processed in large quantities. Then such target gene disruption can be introduced into individuals by generating individuals derived from recombinant ES cells.
In detail, ES cells that have undergone target gene disruption are selected, and chimeric offspring are created using these cells and mouse embryos. The chimeric offspring with germ cells derived from ES cells are crossed for several generations (usually two generations) to create individuals homozygous for target disruption genes (the knockout mice).
However, at present, ES cells that can reliably perform the above method have been obtained only in mice and rats. In the field of livestock and other animals, knockout animals have already been produced by combining genetic targeting disruption using somatic cells with cloning technology, and this will become the mainstream in the future.
Creation of animal models of disease by gene knockout
Knockout animal production is a very effective technique for the development of new experimental animals, especially for the generation of animal models of diseases caused by genetic defects. In our laboratory, we have attempted to establish ES cells as the basis for this technique (Ref. 1), and have actually generated knockout animals. For example, in 1997, we reported the creation of a mouse model of GM1 gangliosidosis, one of the hereditary metabolic diseases lysosomal disease (knockout mice of the acidic β-galatosidase gene; Ref. 2). We are producing various knockout animals in collaboration with other laboratories.
Production of genetically-modified animals by genome editing
- Suzuki et al.(1999) Effect of genetic background on establishment of mouse embryonic stem cells. Exp. Anim. 48(3): 213-216.
- Matsuda et al.(1997). β-Galactosidase deficient mouse as an animal model for GM1-gangliosidosis. Glycoconjugate Journal 14: 729-736.