BOVINE OXYTOCIN TRANSGENES IN MICE - HYPOTHALAMIC EXPRESSION, PHYSIOLOGICAL REGULATION, AND INTERACTIONS WITH THE VASOPRESSIN GENE

To gain insights into the molecular mechanisms that restrict the expre ssion of the oxytocin gene to anatomically defined groups of neurons i n the hypothalamus, we generated transgenic mice bearing bovine oxytoc in genomic fragments, Appropriate neuron specific and physiological re gulation was observed in mice bearing transgene bOT3.5, which consists of the oxytocin structural gene flanked by 0.6 kilobase pair (kbp) of upstream and 1.9 kbp of downstream sequences, bOT3.5 is expressed in oxytocin magnocellular neurons in the mouse supraoptic nucleus and par aventricular nucleus, but transgene RNAs are excluded from vasopressin neurons, Replacement of the drinking diet of the transgenic mice with 2% (w/v) NaCl for 7 days significantly increased the abundance of bov ine oxytocin transcripts in the supraoptic nucleus, but not in the par aventricular nucleus, in parallel with the endogenous mouse oxytocin R NA. Surprisingly, mimicry of the endogenous oxytocin gene expression p attern was lost with larger transgenes, Addition of 0.7 kbp of contigu ous downstream sequences (transgene bOT) or linkage to the bovine vaso pressin gene (transgene VP-B/bOT3.5) repressed hypothalamic expression , No mice were derived bearing transgene bOT6.4, which consists of the oxytocin structural gene flanked by 3 kbp of upstream and 2.6 kbp of downstream sequences, suggesting that the presence of this DNA is detr imental to normal embryonic development, These data suggest that while bOT3.5 contains sufficient cis-acting sequences to mediate expression to particular subsets of hypothalamic neurons, the overall regulation of the oxytocin gene is governed by multiple interacting enhancers an d repressors.