Retroviruses that express different ras mutants cause different types of tumors in chickens

We have used replication-competent retroviral vectors to express avian and murine ras genes in cultured chick embryo fibroblasts (CEF) and in chickens. Since the viral vectors are identical, it is possible to compare the oncogenic potential of the ras genes directly. The normal (12 gly) form of chicken c-Ha-ras is not oncogenic in vivo, nor does high-level expression transform CEF. Expression of murine v-ras or modified forms of chicken c-Ha-ras with either lysine or glutamine at position 12 transforms CEF and causes tumors in birds. However, the oncogenic potential of the transforming ras genes is different; the viruses that express the genes with lysine and glutamine at position 12 cause a distinct spectrum of tumors.