Transcriptional activity of the uteroglobin gene in rabbit endometrial nuclei during early pregnancy

In studies on the regulation of rabbit uteroglobin production by progesterone, we have shown previously that the increase in uteroglobin secretion by the uterus in early pregnancy is preceded by an increase in uteroglobin synthesis and a parallel increase in uteroglobin messenger (m) RNA activity, which is accounted for by a rise in the steady state level of this specific mRNA in uterine epithelial cells. To investigate whether similar changes in the transcriptional activity of the uteroglobin gene occur during this period, we have transcribed endometrial nuclei in a "run-off" endogenous transcription system with [32P]uridine triphosphate as the precursor, given as a short pulse over 7 min at 25 C in vitro. Specific uteroglobin RNA transcripts were quantitated by hybridization of [32P]RNA to nitrocellulose filters containing cloned, full length uteroglobin complementary DNA. The percentage of uteroglobin RNA transcripts rose from day 0 (nonpregnant rabbits) to a peak on day 4 and declined on day 6 of pregnancy. No differences in RNA degradation and no preferential degradation of newly transcribed uteroglobin RNA were found during incubation of nuclei from the different days of pregnancy. The pattern of change in rate of transcription of the uteroglobin gene corresponds to the pattern of change in level of uteroglobin mRNA, suggesting that transcriptional controls are important in regulating the production of uteroglobin in pregnant rabbit uterus.