Molecular cloning of lungfish proopiomelanocortin cDNA

To investigate the evolution of proopiomelanocortin (POMC) from fish to tet rapods, nucleotide sequence of POMC cDNA from a lobe-finned fish, the Afric an lungfish, was determined. POMC cDNA was prepared from lungfish pituitary glands. The POR IC cDNA is composed of 1114 bp, excluding a poly-A tail, a nd encodes 255 amino acids (aa) including a signal peptide of 25 aa. The lu ngfish POMC contains the segment corresponding to gamma-melanotropin (MSPI) , corticotropin, alpha-MSH, beta-MSH, and beta-endorphin at positions (50-6 1), (108-146), (108-120), (178-194), and (197-230), respectively. The lungf ish POMC shows greater sequence identity on average with amphibian (62%), a ncient ray-finned fishes including acipenseriformes and semionotiformes (62 %), and mammalian POMC (52%) than with teleostean (49%), elasmobranch (46%) , and agnathan POMC (31%). Thus, the overall structural feature of lungfish POMC is close to the tetrapod POMCs which contain gamma-MSH and the ancien t ray-finned fishes POMCs containing gamma-MSH-like sequence. However, amin o acid sequence of lungfish beta-endorphin exhibits properties which are sp ecifically observed in the ray-finned fishes and the elasmobranchs. (C) 199 9 Academic Press.