Scientists, including representatives from Sigma-Aldrich, have announced the creation of the first genetically modified mammals developed using zinc finger nuclease (ZFN) technology.
The researchers were from the Medical College of Wisconsin in Milwaukee, Sangamo Biosciences, Sigma-Aldrich, Open Monoclonal Technology, and Inserm.
In a paper published in 24 July 2009 issue of Science, researchers describe the novel application of ZFNs to generate rats with permanent, heritable gene mutations, paving the way for the development of novel genetically modified animal models of human disease.
ZFN technology will make the generation of such animals faster and will create new opportunities in species other than mice.
Howard Jacob, director of the Human and Molecular Genetics Center at the Medical College of Wisconsin, said: 'Until now, rat geneticists lacked a viable technique for "knocking out" or mutating specific genes to understand their function.
'This study demonstrates that ZFN technology bypasses the current need to conduct cumbersome experiments involving nuclear transfer (cloning) or embryonic stem cells and allows rapid creation of new animal models.' In the study published in Science titled 'Knockout Rats via Embryo Micro-injection of Zinc Finger Nucleases', (Geurts, et al) scientists used ZFNs to knock out an inserted reporter gene and two native rat genes without causing measurable effects on other genes.
Importantly, offspring of the ZFN-mutated rats also carried the modifications, demonstrating the genetic changes were permanent and heritable.
Together, these results demonstrate the ability to deliver engineered ZFNs into early-stage embryos and rapidly generate heritable, knockout mutations in a whole organism.
Rats are physiologically more similar to humans than mice are for many traits and are ideal subjects for modelling human diseases.
Extensive genetic characterisation has revealed that approximately 90 per cent of the rat's 25,000-30,000 estimated genes are analogous to those in humans and mice, and their larger size makes them a superior model for drug-evaluation studies using serial sampling.
Generating rats with knockout mutations has been a major challenge, but the new technique will increase the rat's usefulness in research pertaining to physiology, endocrinology, neurology, metabolism, parasitology, growth-and-development and cancer.
Along with his colleagues, Jacob's team hopes to use knockout rats to gain a better understanding of disease processes related to hypertension, heart disease, kidney failure and cancer.
ZFNs are engineered proteins that induce double strand breaks at specific sites in an organism's DNA.
Such double-strand breaks stimulate the cell's natural DNA-repair pathways and can result in site-specific changes in the DNA sequence.
Previously, ZFNs were used to knock out specific genes in fruit flies, worms, cultured human cells and zebra-fish embryos and are now in human clinical trials for the treatment of HIV/AIDS.
This is the first example of successful gene editing in mammalian embryos using this technology.
In the first commercial application of this technique, OMT, a private biotechnology company developing a new rat-based human antibody platform, used Sangamo's ZFNs to knock out the gene encoding rat immunoglobulin M (IgM), an important gene for rat antibody production.
Inactivation of rat IgM expression is the first step in generating rats that exclusively express human antibodies encoded by transgenic human immunoglobulin genes.
