Figure 9. Diagram illustrating the cis-regulatory domains in the vasopressin gene promoter as suggested by the data in this study.

Since the 288 VPI.EGFP construct still maintains the vasopressin MCN specific expression (Fig. 6F) we hypothesize that there is an activator of expression in the Avp MCNs and a possible repressor element with an upper boundary of −288 kbp that inhibits expression selectively in the Oxt MCNs. We further propose that there are at least three enhancer domains upstream of the transcription start site of the Avp gene that are involved in expression in the Avp MCNs, which we designate enhancer 3 located between −2 kbp to −1.5 kbp, enhancer 2 located between −1.5 kbp to −950 bp, and enhancer 1 located between −543 bp to −288 bp (see Fig. 4). The −288 to 116 bp region appears to contain the cell-type specific element(s) (see text), and an osmotically-responsive element also appears to be present within the 288 bp construct (see Fig. S3).