The beta cells within the pancreatic islets of Langerhans are solely responsible for secreting insulin for maintaining proper glucose homeostasis. Defects in beta cell function result in diabetes mellitus, a condition affecting millions of people worldwide. The developmental programs responsible for the differentiation of an insulin-secreting beta cell from progenitor populations have only recently become clearer. Much of what is known about the factors controlling pancreas development stem from studies of the Insulin and Pdx-1 promoters. From this work, the MafA transcription factor was isolated due to its regulation of the Insulin enhancer. MafA expression is unique as compared to any other known beta cell enriched transcription factor, beginning later in development and solely in progenitors fated to become adult beta cells. Because of this unusual expression, the 5'transcriptional control domains of MafA were studied. This promoter has six conserved regions, with Region 3 retaining the most conservation in mammals, birds and Xenopus. Region 3 is also the only domain able to drive beta cell-line specific reporter expression. Published studies demonstrate that Region 3 is at least partially controlled by Pdx-1, Nkx2.2, MafB, and FoxA2, however most of this conserved domain is still uncharacterized.
Specific Aim 1 will define most of the remaining conserved cis-sequences of Region 3 using an unbiased mutagenesis approach and reporter gene assays.
Specific Aim 2 will identify the factors that bind the novel element(s) using techniques including ChIP and gel-shift analyses. These studies may uncover new factors essential for beta cell function. Several lines of evidence suggest temporal changes in factor binding direct unique expression patterns during development and in adults.
Specific Aim 3 proposes a study of binding factors and epigenetic marks across the MafA promoter as a function of time. This will require ChIP using chromatin isolated from mouse pancreata at different developmental and adult stages.
Diabetes is a major health concern that results from a loss of beta cell function;and current insulin replacement does not accurately recapitulate endogenous blood glucose control. Future therapies may involve the manipulation of cell progenitors to become functional beta cells for transplantation to treat a growing number of patients. Studies aimed at understanding the regulation of beta cell genes, like these with MafA, may increase the probability of developing replacement beta cells for improved diabetes treatment.
