Directed genetic modifications in rats was less well developed than that for mice, and historically screens to generate mutations involved N-ethyl-N-nitrosourea, or ENU. ENU is a mutagen that generally causes single base pair mutations in DNA. As ENU treatment is a broad brush that could affect many locations in the genome, resulting rats have to be subsequently screened and examined to determine if genes of interest have been affected. It has been shown that this method is successful for generating mutant rats, including knockout alleles. This strategy remains useful for certain experimental designs, and protocols for this procedure are well developed. Researchers will find that rats from various ENU projects are available and may be suited for their research. To find existing rats generated in this manner, explore the Acquiring Models section.
Advances in technologies for generating transgenic rats are rapidly being made. Utilizing retrotransposons to disrupt genes and genomic regions is widely used as a strategy to generate insertion mutagenic alterations. Transposon mutagenesis, especially using the Sleeping Beauty mechanism, is also in use as a means to generate mutations in rats. Refinements of this method will be increasingly useful to generate modified rats. Both of these methods have generated knockout rats available from the Knock Out Rat Consortium.
Increasing precision in gene targeting, with zinc-finger nuclease technology, has been used to generate heritable, targeted mutations in rats. This important breakthrough enabled successful and precise gene targeting in the rat. Protocols for this strategy are available.
Rat Embryonic Stem Cells
Availability of rat embryonic stem cells (ES) will change the strategies completely, enabling more rapid and targeted developments of genetically modified rats. Methods to culture these cells for use in many types of rat experiments, including targeted genetic modifications, stands to make rapid gains in rat model development.
Combining many of these strategies and technologies, with the appropriate selection of inbred rat models, will enable tremendous progress in cancer research with rat model systems. Further, techniques like the RNA interference strategies described for mice are becoming available for rats as transgenic technologies continue to develop.
It is crucial to be aware of the rules of nomenclature for animal strains and for transgenic rats, so that the users of the models are able to understand the genetic background as fully as possible. Standards for designations of transgenics have been established to ensure that researchers can assess the alterations. Additional information about the nomenclature standards can be found in the section on Breeding Rats.