[A transgenic animal model: new possibilities for cardiovascular research]

By means of molecular biology and genetic research the influence of genetic factors on a great variety of human diseases could be shown. In the field of cardiovascular research the genetic defects of a few monogenetic disorders, such as Marfan's syndrome and hypertrophic cardiomyopathy, have been characterized. In addition, candidate genes for polygenetic diseases, such as arterial hypertension and atherosclerosis, have been cloned. However, the identification of a candidate gene or its mutation does not prove its influence on the phenotype or the final cause of a particular disease. Only a targeted manipulation of a defined candidate gene in a transgenic animal model helps to understand the role of the gene and its product in the whole organism. Transgenic experiments can be divided into gene-addition and gene-deletion models. In a gene-addition experiment a fusiongene is microinjected into a fertilized oocyte. The fusiongene itself consists at least of a regulatory element promoter and of a DNA sequence coding for the gene product (protein) of intended overproduction. The choice of the right promoter is important for obtaining tissue-specific gene expression. The cardiac myosin light chain-2 promoter for example leads to a ventricle-specific gene expression in cardiomyocytes from early embryogenesis through adulthood. In a gene-deletion experiment on the other hand, the target gene is selectively knocked out by homologous recombination in embryonic stem (ES) cells. The selected ES-cells are then injected into blastocysts. If the ES-cells are integrated into the germ line and transmitted to the progeny, a transgenic line is established. This review article describes planning and development of transgenic animals and discusses established transgenic animal model systems with regard to cardiovascular physiology. In addition, animal models which may provide a basis for future gene therapy will be introduced.