Expression of oncornaviral RNA in mouse uterus during pregnancy

The expression of oncornaviral-specific RNA was studied in the NIH Swiss mouse uterus during gestation using hybridization with complementary DNAs synthesized from type C viral high molecular weight RNAs. Following conception there was a marked decrease in the relative concentration of viral RNA below the levels in nonpregnant uteri. Thereafter, the level of viral RNA remained low (less than 30% of prepregnancy levels) until Day 14. Following Day 14 there was a progressive increase in levels of viral RNA and peak levels (greater than or equal to pregestation) were reached just before parturition (Day 18). One day after parturition viral RNA levels were still elevated. A similar profile was observed for p30, a viral-coded protein. We suggest that oncornaviral gene expression is under transcriptional control, most likely by ovarian steroid hormones, and that oncornaviruses can be useful tools to study gene expression in the mammalian uterus.