Structural analysis of the ras transgene in MMTV/v-Ha-ras transgenic mice

: Transgenic animals are becoming increasingly important in laboratory animal research. In cancer research, the role of specific genes in tumorigenesis can be directly tested in live animals by using transgenic animal technology. Since DNA-damaging carcinogens are not required to initiate tumors in transgenic animals, these models are particularly useful in the analysis of genetic alterations associated with tumorigenesis. Southern blot analysis was used to assess the copy number, structure, and methylation status of the ras trans-gene in MMTV/v-Ha-ras transgenic mice. The results indicate that MMTV/v-Ha-ras transgenic mice carry about 20 copies of the ras transgene. The integrated ras transgene is maintained without major rearrangements in normal tissues and in mammary tumors. The ras transgene is methylated in liver, hypomethylated at a single site in normal mammary tissue, and hypomethylated at two sites in mammary tumors. Transgenic animals provide a new model to assess genetic alteration in tumorigenesis.