Transforming potential and growth stimulating activity of the v-fos and c-fos genes carried by avian retrovirus vectors.

To study transforming potential as well as growth stimulating activity of the fos genes on primary cells, we have developed avian retrovirus vectors by constructing derivatives of Rous sarcoma virus DNA in which the v-src gene was replaced by either the v-fos gene of FBJ-MuSV or the mouse c-fos gene. After each derivative was introduced into chicken embryo fibroblasts by transfection, replication-competent viruses that carry the v-fos gene (FJ2) or the c-fos gene (FM4) were recovered. FM4 and FJ2 introduced the fos genes into almost all chicken embryo fibroblasts within 3 days after infection, expressed their gene products, and induced morphological transformation and colony formation in soft agar. Results show that overproduction of the c-fos gene product is enough for cellular transformation not only of rat established fibroblasts as reported previously but also of avian primary fibroblasts. Using this vector system, we have further shown that the c-fos gene and the v-fos gene have biological activities that induce cellular proliferation of chicken neuroretinal cells, which normally stay in the resting stage of growth in monolayer culture.