Expression of ecotropic MuLV in ovaries of SWR/J-RF/J hybrid mice

Abstract

Summary RF/J mice carry three endogenous ecotropic murine leukaemia virus (MuLV) genomes integrated into their chromosomes, while the SWR/J strain has no such provirus. New ecotropic MuLV proviruses are acquired by progeny of some SWR/J-RF/J hybrid females obtained by repeated backcrosses with the SWR/J strain (Jenkins, N.A. & Copeland, N.G., Cell, 1985, 43, 811–819). We have therefore used in situ hybridization to examine the expression of endogenous ecotropic MuLV in the genital tract of these females. We show that ecotropic MuLV RNA is expressed in thecal cells surrounding midstage to late ovarian follicles of SWR/J-RF/J females whose progeny have acquired new proviruses. In contrast, no such expression can be seen either in oviduct and uterus tissues of SWR/J-RF/J hybrids or in the ovary of SWR/J and RF/J inbred mice. Intense and similarly patterned MuLV expression also occurs in the ovary of AKR/J inbred mice, the genome of which occasionally acquires new ecotropic proviruses although at a rather low frequency. These results thus show that ecotropic MuLV are expressed in highly specific target cells of the ovary. The significance of these results for the mechanism of proviral acquisition observed in SWR/J-RF/J hybrid mice is discussed.