Neural-Specific Regulation of POMC Gene Expression

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DESCRIPTION (provided by applicant) This competitive renewal of a Fogarty International Cooperative Award between the U.S.A. and Argentina is in continued support of the scientific goals outlined in its parent grant P01 DK55819, "Neuroendocrine Control of Feeding and Metabolism," subproject 4, "Modulation of Feeding and Metabolism by Opioid Peptides." Obesity and its metabolic sequelae are major health problems world-wide. The opioid peptide beta-endorphin and a family of melanocortin peptides are both important modulators of weight homeostasis and products of the same prohormone, proopiomelanocortin (POMC), that is expressed in specific populations of neurons within the arcuate nucleus of the hypothalamus and the nucleus tractus solitarius in the brain stem. Both of these brain nuclei are key areas involved in the complex integration of neuroendocrine and autonomic control of appetite and feeding. Null mutations of the POMC gene have rarely been associated with early onset morbid obesity and hyperphagia in children. However, genetic studies in several human populations have strongly implicated the POMC gene as a quantitative trait locus for obesity and leptin levels. Mutations in the coding region of the POMC gene that would alter peptide production or function do not account for this linkage, suggesting the alternative possibility of mutations in POMC regulatory sequences. Little is known about the molecular basis for neural-specific expression of the POMC gene, although we hypothesize that dysregulated neuronal POMC expression may be a contributing factor to disorders of energy homeostasis. The overall goal of this FIRCA project is to elucidate the transcriptional machinery responsible for neuronal-specific and leptin-regulated POMC gene expression in the brain and to develop novel molecular tools for the further physiological characterization of POMC peptides in the control of appetite and feeding. This goal will be addressed by the following specific aims: 1) Identify a hypothalamic neural-specific enhancer(s) in the POMC gene utilizing a deletional and mutational analysis in transgenic mice; 2) Characterize the leptin-responsive element in the POMC gene; and 3) Determine a phylogenetic transcriptional code for the POMC gene by sequence comparisons of genomic elements from divergent orders of vertebrate species and the analysis of transgenic mice carrying POMC regulatory sequences of Fugu rubripes, a teleost fish that diverged from placental mammals 450 million years ago.