Complex structural and regulatory evolution of the pro-opiomelanocortin gene family

The melanocortin system is a neuroendocrine machinery that has been associated with phenotypic diversification in a number of vertebrate lineages. Central to the highly pleiotropic melanocortin system is the pro-opiomelanocortin (pomc) gene family, a family of pre-prohormones that each give rise to melanocyte stimulating hormone (MSH), adrenocorticotropic releasing hormone (ACTH), beta-lipotropin hormone, and beta-endorphin. Here we examine the structure, tissue expression profile, and pattern of cis transcriptional regulation of the three pomc paralogs (alpha 1, alpha 2, and beta) in the model cichlid fish Astatotilapia burtoni and other cichlids, teleosts, and mammals. We found that the hormone-encoding regions of pomc alpha 1, pomc alpha 2 and pomc beta are highly conserved, with a few notable exceptions. Surprisingly, the pomc beta gene of cichlids and pomacentrids (damselfish) encodes a novel melanocortin peptide, epsilon-MSH, as a result of a tandem duplication of the segment encoding ACTH. All three genes are expressed in the brain and peripheral tissues, but pomc alpha 1 and alpha 2 show a more spatially restricted expression profile than pomc D. In addition, the promoters of each pomc gene have diverged in nucleotide sequence, which may have facilitated the diverse tissue-specific expression profiles of these paralogs across species. Increased understanding of the mechanisms regulating pomc gene expression will be invaluable to the study of pomc in the context of phenotypic evolution. (C) 2013 Elsevier Inc. All rights reserved.