PDX Regulation of Pancreas Development/Differentation

University Of Pennsylvania, Philadelphia PA

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Abstract

DESCRIPTION (provided by applicant): Maturity onset diabetes (type 2 DM) is a disabling disease that is increasing worldwide in epidemic proportions. One characteristic hallmark of diabetes is a failure of the beta cells of the endocrine pancreas to produce sufficient insulin to meet the body?s needs. In recent years, rapid advances in the human genetics of monogenic early onset forms of type 2 diabetes have revealed a striking role of pancreatic transcription factors in the pathogenesis of type 2 diabetes mellitus. MODY4, in particular, was identified through the intimate connection between transcription factor PDX1/IPF1 regulation of early pancreas development and of differentiated beta-cell function in the fully developed adult organism. Human mutations in PDX1/IPF1 are linked to pancreatic agenesis (homozygous) and early onset monogenic type 2 diabetes mellitus (heterozygous; MODY4). More importantly, IPF-1 mutations are found in approximately 6 percent of French Caucasians with late onset type 2 DM. One mutation in particular, a proline insertion at codon 243 in a hexaproline tract of the C-terminus of PDX1/IPF-1, is linked to autosomal dominant late-onset diabetes in two families. To date, no studies have shown an effect of C-terminal truncation or mutation on transactivation by Pdx1/Ipf1, yet the human mutations clearly point to an important function for this region. Therefore, we hypothesize that in vivo analysis of C-terminal mutation in mice will be required to study the role of the PDX C-terminus in islet development and function. We propose in Aim 1 to investigate the development and function of the pancreas in mice harboring disruption of the Pdx 1 C-terminus. Two lines of "knock-in" mice harboring either the codon 243 proline insertion or a premature stop codon replacing serine 210 will be created. Homozygous and heterozygous mutant mice will be evaluated morphologically and physiologically on genetic backgrounds susceptible to diabetes and obesity. In Aim 2 we will investigate the Pdx 1 C-terminus as a protein-protein interaction domain. We will identify protein partner(s) by yeast two hybrid screening and we will over express the PDX C-terminus in vivo predicting that this will disrupt pancreas development and/or function through competition with endogenous Pdx 1 for a critical interaction. The proposed studies will improve our understanding of PDX protein function I and may have implications for the design of future treatment strategies for type 2 diabetes mellitus.