Lifelong genetic minipumps.

Most physiologists working with animals are familiar with osmotic minipumps. These surgically implanted devices can, for a limited period, administer a reagent at a constant predetermined rate that is unaffected by concurrent procedures. The investigator can then test the physiological effects of other treatments knowing that the animals' homeostatic responses will not be able to alter the dose of the pumped reagent. To develop the genetic equivalent of a lifelong minipump, simply inherited as an autosomal dominant, we here combine three of our previously described strategies, genetic clamping, single-copy chosen-site integration, and modification of untranslated regions (UTRs). As a test of the procedure, we have generated a series of intrinsically useful animals having genetic minipumps secreting renin ectopically from the liver at levels controlled by the investigator but not subject to homeostatic changes. To achieve the different dosage levels of these genetic minipumps, we altered the UTRs of a renin transgene driven by an albumin promoter and inserted it into the genome as a single copy at the ApoA1/ApoC3 locus, a locus that is strongly expressed in the liver. The resulting mice express plasma renin over ranges from near physiological to eightfold wild type and develop graded cardiovascular and kidney disease consequent to their different levels of ectopically secreted renin. The procedure and DNA constructs we describe can be used to generate genetic minipumps for controlling plasma levels of a wide variety of secreted protein products.