Characterization of the expression of cellular retrovirus genes and oncogenes in feline cells

Expression of endogenous retrovirus genes and two different cellular oncogenes (c-onc genes) was examined at the transcriptional level in a variety of normal and lymphoma/leukemia tissues of the domestic cat. The two oncogenes, c-myb(related to avian myeloblastosis virus) and c-myc(related to avian myelocytomatosis virus) were selected for their association with the induction of hematopoietic malignancies, when present in the transforming retroviruses. Tissue-specific expression of endogenous feline leukemia virus (FeLV)-related genes was detected in cellular subpopulations of the cat placenta by in situ method of hybridization. Gel blotting analysis of placental poly(A)-selected RNA revealed that the FeLV-related RNA species were primarily subgenomic, representing the env gene region of the endogenous provirus elements. Like the endogenous retrovirus genes, c-myb and c-myc loci of the cat genomic DNA were also transcribed at differential levels in normal tissues of the cat. Dot-blot hybridization analysis showed that the expression of these two oncogenes was linked to growth and development as it varied with the gestational age of the fetus and from fetal to adult tissues. Among the major hematopoietic organs, spleen and bone marrow contained both c-myb and c-myc transcripts, while thymus preferentially expressed the c-myb gene. In contrast to the low level of c-myc expression in fetal thymus tissues, enhanced c-myc expression was detected in all five thymomas tested and also in several other neoplasms including two granulocytic leukemias. The feline c-myb gene was not very active in granulocytic leukemias or in three of the five thymomas. RNA gel blotting analysis of poly(A)-selected RNA of a thymoma and its lymph node metastasis showed identical pattern of c-myc transcripts.