Parsing the molecular code for two neuronal enhancers that underwent convergent evolution

NASIF, F. DE SOUZA, R. LÓPEZ-LEAL, M. RUBINSTEIN

Puerto Madryn

Congreso; XLVI Reunión anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

SAIB

The proopiomelanocortin gene (POMC), encodes a prohormone that is expressed mainly in the pituitary and the arcuate nucleus of the hypothalamus, playing a central role in the stress response and energy balance, respectively. Hypothalamic POMC expression is driven by two different enhancers named nPE1 and nPE2. Although these two enhancers are evolutionarily unrelated, they are both able to drive Pomc expression to the same group of hypothalamic neurons. Expression studies in transgenic mice led us to the identification of a 140 bp region within nPE1 that is necessary and sufficient to drive reporter gene expression to POMC neurons. A comparative analysis of this critical nPE1 region with those previously identified in nPE2 evidenced a small number of short sequences that are present in both enhancers. To test the hypothesis that these shared sequences are critical for enhancer function, we designed transgenic constructs carrying a set of mutations that simultaneously eliminated all the identified sites. These transgenes failed to drive reporter gene expression to hypothalamic neurons demonstrating that the mutated sites play a fundamental role in the neuronal-specific regulation of Pomc. Further ongoing studies are aimed at determining the relative importance of each of the identified elements shared by nPE1 and nPE2.