THE SHEEP ESTROGEN-RECEPTOR - CLONING AND REGULATION OF EXPRESSION INTHE HYPOTHALAMOPITUITARY AXIS

We have prepared an ovine pituitary cDNA library, isolated a clone con taining the full-coding sequence of estrogen receptor (ER) cDNA, and d etermined its primary structure. This cDNA encodes a protein of 596 am ino acids which shows great homology to other mammalian ER sequences, the highest degree being 95% with the porcine receptor. Northern blot analysis of ovine pituitary RNA revealed a 6.3 kb transcript. This rec eptor was showed to bind a consensus ERE and to be transcriptionally a ctivated by E2. Studies investigating the pattern of expression of the ovine ER mRNA were also carried out, using the reverse transcription/ PCR technique. Expression of ER mRNA was analyzed in ram pituitary and hypothalamus after contrasted light regimen and castration. Results s howed that the light regimen had no effect on ER mRNA expression where as castration induced a slight (similar to 20%) but significant increa se of ER mRNA expression at both the hypothalamic (P < 0.05) and pitui tary (P < 0.01) levels, indicating a negative regulation of ER gene ex pression by testicular steroids. Since we have previously shown no var iations in ER protein levels after castration, data suggest the activa tion of a complex pattern including both transcriptional and post-tran scriptional regulatory mechanisms in the ram hypothalamo-pituitary axi s.