[Transgenic mice and their use in cancer study].

The ability to introduce the cloned gene into the mouse germ line has made possible to analyze the cis-acting DNA sequence which is involved in the tissue-specific and developmental regulation of the gene. In addition, this system can also be applied to analyze the patho-physiological roles of the introduced gene product within the mouse whole body. Therefore, this system is one of the best approaches to analyze the mechanism of oncogenesis. The chromosomal translocation is one of the mechanisms leading to the activation of oncogene. In the case of lymphoid cell tumors, the reciprocal translocation between chromosome No. 8 and No. 14 is frequently observed. With this translocation, c-myc gene can be activated by the enhancer of immunoglobulin heavy chain (E mu). We and others have demonstrated that the E mu-myc gene could induce lymphomas in transgenic mice. Following these observation we have currently many examples that activated oncogene can induce variety tumors, giving basic knowledge about the relationship between activated oncogene and cell-type specificity of tumor. On the other hand, molecular mechanism of oncogenesis which is caused by viruses such as hepatitis B virus (HBV) or human T cell leukemia virus (HTLV) is totally unknown. One main reason is the absence of animal model for these diseases. To overcome this problem, we have attempted and succeeded to produce a transgenic mouse model which consistently produces HBV. Using these mice, it will be possible to elucidate the molecular mechanism of development of hepatitis and hepatocellular carcinoma.