Fv-2 locus controls expression of Friend spleen focus-forming virus-specific sequences in normal and infected mice

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Abstract
Normal hemopoietic cells express RNA sequences that are homologous to sequences specific for the Friend erythroleukemia virus genome. The Fv-2 locus, the major genetic determinant controlling host susceptibility to erythroleukemia induction by Friend leukemia virus, also controls the expression of endogenous sequences related to the replication-defective component of Friend leukemia virus, Friend spleen focus-forming virus (SFFV), in normal uninfected mice. Two independent congeneic pairs of mice [C57BL/6 (B6) and B6.S; B6 and B6.C(H-7b)], differing only in a small region of the mouse genome including the FV-2 locus, were used. In both cases, molecular hybridization analysis indicated that the presence of SFFV-related RNA sequences in normal mice was associated with the Fv-2s allele: bone marrow or spleen cellular RNA from Fv-2rr B6 mice contained no detectable SFFV-related sequences, whereas their congeneic Fv-2ss pairs contained relatively high levels of these RNA sequences. The absence of these RNA sequences in Fv-2rr mice was not due to deletion of these sequences from the DNA of Fv-2rr mice. Repopulation of lethally irradiated Fv-2rr mice with syngeneic Fv-2rr bone marrow cells did not lead to any increase in the levels of these SFFV-related RNA sequences, suggesting that the expression of these sequences is still reduced or inhibited in actively cycling Fv-2rr hemopoietic cells. Infection with Friend leukemia virus resulted in the appearance of high levels of RNA homologous to SFFV-specific sequences in the leukemic spleens of B6.S (Fv-2ss) mice, whereas these cellular RNA sequences could not be detected in the spleens of Friend virus-infected B6 (Fv-2rr) mice. The demonstration that the same gene locus controls both the expression of exogenous SFFV-specific sequences and erythroleukemia induction by Friend leukemia virus suggests that these sequences may be necessary for erythroleukemic transformation. The finding that the Fv-2 gene locus controls the expression of endogenous SFFV-related sequences suggests that these sequences may also be involved in normal hemopoiesis.