Proto-oncogene expression in avian hematopoietic tissues

Abstract

Previous findings from this laboratory (Kim & Baluda, 1988) have shown that the proto-oncogenes ETS, FPS, MHT (RAF), MYC and REL are expressed in avian myeloblastosis virus (AMV)-transformed cells, whereas the MYB gene is repressed. In this study five different chicken hematopoietic tissues which contained varying concentrations of target cells for AMV transformation were analyzed to determine whether the expression of these proto-oncogenes resulted from, or was altered by, v-myb-induced leukemogenesis. Poly-A+ RNA from hematopoietic cells of 11-13 day yolk sac, 16 day embryonic spleen, 1 day post-hatch bursa of Fabricius, bone marrow and thymus, as well as from chicken embryonic fibroblasts (CEF) was examined by Northern blot analysis. All five proto-oncogenes were found to be expressed in the normal hematopoietic tissues. The ETS, MHT (RAF), MYC, and REL genes, but not FPS, were expressed in CEF. The expression of these five proto-oncogenes was not quantitatively or qualitatively altered in AMV-transformed myeloid cells as compared with their normal counterparts. While their expression is part of the hematopoietic phenotype of the target cells and as such is necessary for susceptibility to AMV transformation, it is not sufficient because thymocytes with a high level of expression are not transformed. This is in contrast to MYB expression, which is totally repressed in leukemic cells but probably not as a result of v-myb expression.