Cloning of a neoteleost (Oreochromis mossambicus) proopiomelanocortin (POMC) cDNA reveals a deletion of the gamma-melanotropin region and most of thejoining peptide region: implications for POMC processing

A signature feature of tetrapod pro-opiomelanocortin (POMC) is the presence of three melantropin (MSH) coding regions (a-MSH, beta-MSH, gamma-MSH). Th e MSH duplication events occurred early during the radiation of the jawed v ertebrates well over 400 million years ago. However, in at least one order of modern bony fish (subdivision Teleostei; order Salmoniformes; i.e. salmo n and trout) the gamma-MSH sequence has been deleted from POMC. To determin e whether the gamma-MSH deletion has occurred in other teleost orders, a PO MC cDNA was cloned from the pituitary of the neoteleost Oreochromis mossamb icus (order Perciformes). In O. mossambicus POMC, the deletion is more exte nsive and includes the gamma-MSH sequence and most of the joining peptide r egion. Because the salmoniform and perciform teleosts do not share a direct common ancestor, the gamma-MSH deletion event must have occurred early in the evolution of the neoteleost fishes. The post-translational processing o f O. mossambicus POMC occurs despite the fact that the proteolytic recognit ion sequence, (R/K)-X-n-(R/K) where n can be 0, 2, 4, or 6, a common featur e in mammalian neuropeptide and:polypeptide hormone precursors, is not pres ent at several cleavage sites in 0. mossambicus POMC. These observations wo uld indicate that either the prohormone convertases in teleost fish use dis tinct recognition sequences or vertebrate prohormone convertases are capabl e of recognizing a greater number of primary sequence motifs around proteol ytic cleavage sites. (C) 1999 Elsevier Science Inc. All rights reserved.