Identification of the enhancers that direct expression of the proopiomelanocortin gene to the hypothalamus of transgenic mice

DE SOUZA FS; SANTANGELO AM; BUMASCHNY VF; LOW MJ; RUBINSTEIN M

Pinamar, Argentina

Congreso; XLI Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology (SAIB), X Congress of the Panamerican Association for Biochemistry and Molecular Biology (PABMB), and the XX Annual Meeting of the Argentine Society for Neurochemistry (SAN; 2005

Background: Proopiomelanocortin (POMC) is a prohormone produced mainly in the pituitary and in neurons of the arcuate nucleus of the hypothalamus. Hypothalamic POMC has been implicated as a key component in the control of energy homeostasis, being regulated by the hormone leptin. Hypothalamic POMC is processed into a-melanocyte-stimulating hormone (a-MSH), which signals via MC4 receptors triggering an energy-spending physiological response, reducing feeding and increasing metabolic rate. Indeed, mice and humans mutant for POMC develop severe early-onset obesity, and genetic scans have found a strong association of the POMC locus and obesity-related traits in several human populations. Objective: Find the enhancer regions which direct POMC gene expression to hypothalamic neurons in mammals. Results: We performed a deletion analysis of the murine POMC gene in transgenic mouse assays and found a 4 kb-region located between –13 and –9 kb from the POMC gene which can direct proper transgene expression to POMC-arcuate neurons from a heterologous minimal promoter. The region contains two elements of 450 and 150 bp highly conserved among mice, men, rat, chimpanzee, dog and cattle which we termed nPE1 and nPE2, respectively. Deletion analysis shows that the absence of either region separately does not abolish correct arcuate transgene expression but that the deletion of both does, showing that nPE elements are needed for POMC expression in hypothalamic neurons. In addition, we show that human nPE elements can also drive transgene expression to the POMC-neurons of transgenic mice. Conclusions: We identified two novel enhancers conserved in all mammals which are necessary and sufficient to direct POMC expression to the hypothalamus. Our results will be useful in finding whether polymorphisms in POMC regulatory regions might influence the tendency to gain excessive weight in human populations.