Proto-oncogene expression in chicken leukemic cells induced by avian myeloblastosis virus

Sixteen proto-oncogenes which have generated retroviral oncogenes were tested for their expression in chicken leukemic cells induced by avian myeloblastosis virus (AMV) and five were found to be expressed (c-ets, c-fps, c-mht, c-myc, and c-rel). The size of the c-fps transcript (4.0 kb) was not in good agreement with the size (approximately 3.0 kb) previously reported but was uniform in the leukemic cells from 10 different chickens. The size of the other proto-oncogene transcripts appeared normal. The five expressed proto-oncogenes represent cellular genes involved in hematopoiesis. Interestingly the c-myb gene was not expressed in any of the leukemic cells despite its expression in the immature myeloid cells which are targets for AMV transformation. This could represent down regulation of c-myb by v-myb or a differentiation-related arrest of c-myb expression. The leukemic phenotype induced by v-myb may therefore become expressed at a stage of myeloid differentiation when c-myb expression is repressed.