Presence and expression of Friend erythroleukemia virus-related sequences in normal and leukemic mouse tissues

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The nature and distribution of sequences related to the murine erythroleukemia virus, Friend spleen focus-forming virus (SFFV), have been analyzed by using a radioactive cDNA probe specific for the SFFV genome (cDNAsff). From the proportion of high molecular weight viral [32P]RNA which hybridized to cDNAsff, it was estimated that these sequences represent about 50% of the SFFV genome, indicating a genetic complexity of about 3300 nucleotides. cDNAsff hybridized extensively (80-95%) to SFFV virion RNA and to cellular RNA from murine and rat cells productively or nonproductively infected with SFFV. Only background homology was detected between cDNAsff and viral RNA from a number of murine [Friend murine leukemia virus (MuLV), Moloney-MuLV, and Kirsten sarcoma virus] and nonmurine (Rous sarcoma virus, feline leukemia virus, baboon endogenous virus, and Mason—Pfizer mammary tumor virus) retroviruses. Limited homology was also detected to a number of murine xenotropic and mink cell focus-inducing viruses (20-35%) as well as Rauscher leukemia virus (50%). Nucleotide sequences homologous to cDNAsff were also detected in the DNA of normal cells of several mouse strains as single or a few copies per cell. Thermal denaturation analysis indicated that duplexes formed between cDNAsff and normal DBA/2J cellular DNA have a reduction in melting temperature of 2°C when compared with the dissociation of hybrids between cDNAsff and homologous sequences in SFFV-infected mouse spleen cell DNA. Examination of cellular RNA from uninfected mouse cells indicated that SFFV-related RNA sequences were also expressed in varying degrees in different tissues of adult DBA/2J mice. The highest amounts were observed in cells from bone marrow and spleen, whereas considerably lower amounts were found in cells from the thymus and kidney. No SFFV-related sequences could be detected in RNA extracted from liver, muscle, or fibroblasts. The presence of these SFFV-related sequences in normal, uninfected mouse cell DNA and their differential expression in hematopoietic tissues suggest that these sequences may be an integral part of the program of both normal and leukemic hematopoietic cell differentiation.

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