A genomic element within the third intron of the human oxytocin receptor gene may be involved in transcriptional suppression.

The human oxytocin receptor (OTR) gene comprises a large (> 10 kb) third intron between the regions encoding the transmembrane domains six and seven. It has been shown for other genes that transcriptional control elements may reside within such introns, and that these may correlate with changes in the methylation status of the DNA. Methylation mapping indeed indicated that within this third intron there was a region which appeared to be hypermethylated in non-expressing tissues, but relatively hypomethylated in the myometrium of the cycle and at term, when the OTR gene is upregulated. We then employed in vitro nuclear protein-DNA binding assays to evaluate the importance of this region in the control of the human OTR gene. As source of nuclear proteins we have compared a non-expressing tissue, human peripheral blood leucocytes, with human myometrium from the cycle (low expression) and from term pregnancy (high expression). It could be shown that a specific motif of ca. 10-15 nucleotides close to the middle of the third intron specifically binds nuclear proteins correlating with the down-regulated state of the gene. The accumulated data suggest that this intronic element is specifically binding nuclear protein(s) associated with a suppression of OTR gene activity.