Cloning and Sequencing of Two POMC cDNAs in Rainbow Trout zy (Oncorhynchus mykiss) Effect of Sex Steroids on zyx the Expression of the POMC Genes zyx ISABELLE CHAUVEAU," GILLES SALBERT," DENIS TRANCHAND BUNEL,' HUBERT VAUDRY,C YVES VALOTAIRE,~ AND PATRICK zyxw JEGO" "Laboratoire de Physidogie des ~ ~~ulatio~~ bLaboratoire de Biologie Mole'culaire URA CNRS 256 35042 Rennes Cedex, France cEur~pean Institute for Pepride Research Laboratory of Molecular Endocrinology URA CNKS 650 University of Rouen zyxw 76134 Mont-Saint-Aignan, France The biologically active peptides ACTH, melanocyte-stimuiating hormones (MSHs), and endorphins derive from a single precursor protein called proopiomela- nocortin (POMC). The isolation and sequencing of salmon POMC-derived pep- tides' has suggested the presence of two POMC genes in salmon, although only one salmon POMC cDNA has been sequenced so far.' In mammals, POMC- derived peptides are involved in the control of GnRH secretion and reproductive behavior. In order to further investigate the possible interactions between POMC- derived peptides and reproductive functions, we have cloned and sequenced two different POMC cDNAs in the rainbow trout. These cDNAs have been isolated from a pituitary pars intermedia cDNA library by using a rat POMC probe (a gift from Dr. J. L. Roberts, New York). Northern blot analysis revealed that the POMC mRNA lengths were zy 1.4 kb (POMC A) and 1.8 kb (POMC B). The overall homology between the two coding sequences was rather low (51%) despite some highly conserved regions zy (a- and /3-MSH, CLIP, P-endorphin). When the deduced amino acid sequences were considered, the overall homology between the two POMCs fell to 43%. These results demonstrate the presence and expression of two POMC genes in trout. Our results confirmed the general organization proposed for the two salmon POMCs by Kawauchi.' The trout POMC A corresponds to salmon NPP I, a-MSH I, CLIP I, 6-MSH I, and /$endorphin 11, while the trout POMC B corresponds to salmon NPP 11, a-MSH 11, CLIP 11, P-MSH 11, and @endorphin I. Furthermore, no yMSH sequence was found in any of the trout POMCs. The POMC A cDNA exhibits a very long coding sequence, leading to a C- termin~ly extended form of endorphin, containing three potential dibasic cleav- age sites. If the most 5' cleavage site is actually processed in uiuo, a new peptide 476