Expression of human polypeptide hormones in transgenic and transkaryotic mice: Implications for the treatment of human genetic disease

This thesis presents studies in two related areas of mammalian genetics: the regulation of polypeptide hormone gene expression and the development of a model somatic cell gene therapy system.;The human growth hormone gene (GH-A) is expressed in pituitary somatotrophs and is involved in the regulation of growth and metabolism. A mouse metallothionein-I/GH-A fusion gene was used to generated transgenic animals, and when several of the resulting mice and their offspring were treated with glucocorticoids, serum GH-A and hepatic GH-A mRNA levels were elevated. Evidence is presented demonstrating that DNA sequences responsible for the observed inductions must be present in the GH-A portion of the fusion gene.;Little is known regarding the structure, function, or site of expression (if any) of the growth hormone variant gene (GH-B). Data is presented demonstrating that the gene directs production of a functional growth hormone like-protein in both transiently transfected tissue culture cells and in transgenic mice.;As a model somatic cell gene delivery system, cultured mouse L cell fibroblasts were transfected with a mouse metallothionein I/human growth hormone gene and placed in several locations within syngeneic animals. This study demonstrates that cultured cells can be engineered to produce a protein that they normally do not synthesize, and that when implanted into animals, the cells function in a predictable, modifiable fashion. This technique has been termed "transkaryotic implantation," with "transkaryotic" suggesting that the nuclei of the implanted cells have been altered by the addition of DNA sequences by transient or stable transfection.;Insulin is a polypeptide hormone that plays the predominant physiologic role in the regulation of fuel homeostasis in the organism. In order to study the regulation of serum insulin levels and of insulin gene expression, a series of transgenic mice containing the human insulin gene was generated. The human insulin gene is expressed tissue specifically in the islets of these transgenic mice, and their serum human insulin levels are properly regulated by glucose, amino acids, and tolbutamide, an oral hypoglycemic agent.