Resistance to Friend leukemia virus in transgenic mice expressing the native Fv-4 gene

Fv-4 is a truncated ecotropic retrovirus gene that codes for an envelope protein under control of a cellular promoter. It confers resistance to ecotropic murine leukemia viruses. Transgenic mice were derived using the native Fv-4 gene as the construct for microinjection. Two founder mice were derived. In both founder lines, there was no detectable expression of the transgene or resistance to Friend murine leukemia virus (FrMLV) in hemizygotes. In one line, the resistance was observed in homozygotes with Fv-4 RNA formation in the thymus but not in the spleen or in other tissues. In the other founder line, a homozygous male was identified. Double integrants, derived from breeding this homozygous male to homozygous females from the other founder line, were also resistant. These results indicate that the native gene confers the resistance in homozygous transgenic mice or double integrants derived from different founders but not hemizygotes.