#2 Current State of Production, Research and use of Transgenic Laboratory Animals.
Transgenic techniques have prompted major contributions to a number of research areas of biology and medicine. Transgenic mice are produced by three methods: transfection with viral vectors. DNA injection of egg nuclei, and from genetically
altered embryonic stem cells Most widely used in mice and the only available method for other laboratory mammals is that of DNA injection. By this method the genomic insertion of foreign DNA relies on enzymatic processes active at random breaks in chromosome. In addition. ligation and homologous recombination processes take place between injected DNA molecules in the nucleoplasm, resulting in multiple copies per insert. Gene expression from an inserted transgene varies
considerably depending on its position in the genome‘ and it is only recently that attempts to overcome this has been successful. Animals showing symptoms known from human diseases can be used as models for the development of new therapies. Many transgenic animal models have been made for both dominantly and rocossively inherited diseases. but still only a few for polygenic or complex immunological and cardiovascular diseases, and for the acquired infection and cancer diseases. These models are used extensively in both basic and applied biomedical research. Future improvements in the transgenesis techniques can result from the use of more suitable retroviral vectors and from the use oflarger DNA constructs for pronuclear injection. These could accommodate multiple genes as well as their genetic co-ordination. Finally, there will be wide applications for the current development of genetic switches for turning transgenes off and on by the use of site specific recombination.