Expression of the c-rel and c-myc proto-oncogenes in avian tissues.

Reticuloendotheliosis virus (REV-T) transforms very immature avian lymphoid cells and induces a rapidly fatal lymphoma. The viral oncogene, v-rel, encodes a 59 kDa phosphoprotein which is complexed with cellular proteins in the cytosol of REV-T transformed lymphoid cell lines. The proto-oncogene, c-rel, has been highly conserved among both vertebrate and invertebrate species. The expression of both the c-rel and c-myc protoncogenes was characterized during avian development. Two distinct rel-related transcripts were detected. A 4.0kb mRNA was the principal transcript expressed in cells of hematopoietic origin with highest levels detected in bursa, thymus, and spleen tissue obtained from hatched birds. Relatively low levels of this 4.0 kb transcript were detected in nonhematopoietic tissues. Thus, the distribution of this mRNA correlated with the presence of target cells for transformation by v-rel. The 4.0 kb c-rel transcript had a half-life of nearly 2 h in an avian lymphoid cell line. A second rel-related transcript was identified in the ovary of young hens and appeared to be expressed either in primary oocytes or in the developing follicle. This 2.6 kb c-rel mRNA was detected at substantially lower levels in cells of hematopoietic origin. Using radiolabeled RNA probes, the 2.6 kb c-rel transcript was not detected in liver, brain, testes, or muscle. The c-myc proto-oncogene was also expressed in cells of hematopoietic tissue and ova obtained from hatched birds. While intermediate RNA levels were observed in muscle and liver cells, the c-myc gene was not expressed in avian testes.