Transcriptional Regulation of Pituitary POMC Is Conserved at the Vertebrate Extremes Despite Great Promoter Sequence Divergence

The stress response involves complex physiological mechanisms that maximize behavioral efficacy during attack or defense and is highly conserved in all vertebrates. Key mediators of the stress response are pituitary hormones encoded by the proopiomelanocortin gene (POMC). Despite conservation of physiological function and expression pattern of POMC in all vertebrates, phylogenetic footprinting analyses at the POMC locus across vertebrates failed to detect conserved noncoding sequences with potential regulatory function. To investigate whether ortholog POMC promoters from extremely distant vertebrates are functionally conserved, we used 5′-flanking sequences of the teleost fish Tetraodon nigroviridis POMCα gene to produce transgenic mice. Tetraodon POMCα promoter targeted reporter gene expression exclusively to mouse pituitary cells that normally express Pomc. Importantly, transgenic expression in mouse corticotrophs was increased after adrenalectomy. To understand how conservation of precise gene expressi...