2 ORPHAN RECEPTORS BINDING TO A COMMON SITE ARE INVOLVED IN THE REGULATION OF THE OXYTOCIN GENE IN THE BOVINE OVARY

The peptide hormone oxytocin is highly expressed in the hypothalamus w ithin only a small number of magnocellular neurons. However, it is als o expressed in a much larger number of cells in the bovine corpus lute um at high levels in an estrous cycle-dependent manner. By using nucle ar extracts from this tissue for in vitro binding studies, two protein complexes have been shown to bind to a common site in the bovine oxyt ocin promoter. One of these proteins has been identified as the bovine homologue of the chicken ovalbumin upstream promoter transcription fa ctor (COUP-TF). The second protein is here characterized as the bovine homologue of a tissue-specific transcription factor, steroidogenic fa ctor 1 (SF-1). The relative expression of these two factors during lut eal development correlates with the level of luteal oxytocin gene expr ession, with SF-1 being the factor binding to the promoter of the oxyt ocin gene when this promoter is activated. Cotransfection experiments using the murine testicular cell line TM4 show that SF-1 can stimulate the expression of a transfected oxytocin gene, suggesting that SF-1 m ay be involved in upregulation of the oxytocin gene in vivo, possibly by transducing a stimulatory signal to the RNA polymerase.