Transgenic Animals

George A Kollias, Department of Molecular Genetics, Hellenic Pasteur Institute, Athens, Greece

Transgenic animals are those that, as a consequence of experimental DNA transfer application, have exogenous DNA integrated in their germ line. The integrated DNA may or may not derive from the same species as the host genome; it may or may not encode for a functional gene; and it may or may not be targeted to an intended site of incorporation in the genome. Although the term 'transgenic animal' fully represents all such cases, more specific terms such as 'knockout animals' or 'mutant animals' are used to notify the targeted disruption or mutagenesis of selected endogenous gene sequences in the germ line of animals. Most of what we know of transgen-esis in animal species comes from experimental work on the mouse but transgenic technology has been also successfully applied in insects, domestic livestock, poultry and fish.

Historically, the first transgenic mouse was created by Jaenisch in 1976, by infection of preimplantation embryos with murine leukemia virus which resulted in germline integration of the virus. Today, almost all transgenic mice arc produced by pronuclear microinjection of DNA into fertilized eggs, a technique introduced in 1980 by Gordon and colleagues (Figure 1). One of the most important properties of transgenesis in animals is that the introduced trans-genes usually retain their natural cell-type specificity of expression but show perturbed quantitative regulation. This selective perturbation of gene expression in whole animals allows us to interfere with physiological processes and thereby to reveal gene function. The use of transgenic animals in biological and biomedical research has increased dramatically during the last decade and has advanced greatly our understanding of gene structure and function in physiological and pathological processes. In addition, biotechnological applications of transgenesis in large animals have provided a potential for its commercial exploitation in agriculture and biotechnology.

Figure 1 Microinjection of DNA into one of the pronuclei of a mouse zygote. (Photo taken by Sally Hill, Department of Molecular Genetics, Hellenic Pasteur Institute).
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