Glucokinase (GK), a high Km hexokinase, is a key component of the glucose sensing apparatus of pancreatic beta cells and mutations in the human glucokinase gene are linked to the development of Maturity Onset Diabetes of Youth (MODY), an early onset form of NIDDM. While the GK gene has been established as one of only a few authentic diabetes genes, it is not understood how mutations in this gene actually cause hyperglycemia. Recent data suggests that the current notion that hyperglycemia in GK-deficient NIDDM is due primarily to a glucose sensing defect by the beta cell is overly simplistic. First, they have identified GK in extrapancreatic neural and neuroendocrine cells that, like pancreatic beta cells, may also be able to sense fluxes in glucose concentration. Second, GK ribozyme transgenic mice that have reduced amounts of GK in the beta cells are less severely affected than might have been predicted. Additional studies are necessary, therefore, to understand more about the cell-specific expression and function of GK in extrapancreatic neural and neuroendocrine cells and the pathogenesis of GK- deficient NIDDM. Four complementary Specific Aims are proposed:
Specific Aim 1. Produce and characterize transgenic mice that contain copies of an 83 kb fragment of the mouse glucokinase gene and test the ability of the transgene to rescue the lethal embryonic phenotype observed with the total knock-out of the glucokinase gene.
Specific Aim 2. Use a strategy of targeted oncogenesis in transgenic mice to identify and characterize extrapancreatic neuroendocrine cells that express the islet glucokinase isoform.
Specific Aim 3. Identify and characterize negatively-acting cis-regulatory elements, and their binding protein(s), that repress expression of the upstream glucokinase promoter.
Specific Aim 4. Establish a model system in which glucokinase can be conditionally removed from different cell types of the mouse with initial emphasis being placed on eliminating glucokinase in pancreatic beta cells.
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