Transcription elements and functional expression of proopiomelanocortin genes in the pituitary gland of the barfin flounder.

Proopiomelanocortin (POMC) is the precursor of adrenocorticotropin, melanocyte-stimulating hormone, and endorphin. Barfin flounder Verasper moseri possesses three POMC mRNAs. In this study, we determined the amino acid sequences of POMC-A, POMC-B, and POMC-C in this fish and investigated the effects of black or white background on the expression of these genes. The three POMC genes (POMCs) were composed of three exons and two introns, wherein all the hormonal segments were encoded on the third exon, a pattern similar to that in other vertebrates. Intron B of POMC-A and POMC-B contained microsatellites of CA repeats, indicating that these two genes diverged from a common immediate ancestor by a recent duplication event. The 5'-flanking regions of the POMC-A (-1051 to -1), POMC-B (-1465 to -1), and POMC-C (-870 to -1) genes contained TATA boxes, Tpit, cyclic AMP response element-like elements, E boxes, and other elements. POMC-B and POMC-C also contained CCAAT boxes. The expression of the three POMCs seems to be regulated by synergistic interactions among a variety of transcription factors. The transfer of barfin flounder between tanks with different colors showed that in response to a black or white background, the expression of these POMCs did not always show similar profiles both in the neurointermediate lobe and pars distalis of the pituitaries. Since these POMCs are expressed in a single cell, the non-synchronous expression of these genes suggests that different sets of transcription factors are associated with the transcription of each gene.