[Receptor and disease: genetic perspective]

Cells in higher animals communicate with each other using hundreds of kinds signaling molecules. Most of these signaling molecules are secreted from the signaling cell by exocytosis or diffusion. Regardless of the nature of the signal, the target cell responds by a specific protein called a receptor. It specifically binds the signaling molecule and then initiates a response in the target cell. Many genes for receptor molecules have been identified and mutations in many receptors are shown to be related to human diseases. In general, both genetic and environmental factors are involved in determining phenotypes including disease susceptibility. As the relative significance of genetic and environmental factors varies from disease to disease, we need animal models for human diseases to analyze these factors. It is now possible to manipulate mouse embryos to produce transgenic and knockout mice. These mice are quite useful for analyses of receptor functions and pathologic processes of disease development. As we only have about 6,000 mutant mice, we still need to produce at lease 94,000 other kinds of mice. To achieve this goal, we have to carry out random mutagenesis, instead of homologous recombination in ES cells.