Identification and expression of two oxytocin/vasopressin-related peptides in the cuttlefish Sepia officinalis

Two novel members of the oxytocin/vasopressin superfamily have been identified in the cephalopod Sepia officinalis. Oxytocin/vasopressin gene sequences were cloned by Race PCR. The two precursors we identified exhibit the classical organization of OT/VP superfamily precursors: a signal peptide followed by a nonapeptide and a neurophysin domain. The neurophysin domain is entirely conserved for the cuttlefish precursors, but the nonapeptides and the signal peptides differ. The first nonapeptide, called sepiatocin, is highly homologous to Octopus vulgaris octopressin. The second nonapeptide, called pro-sepiatocin, shows sequence homologies with a Crustacean oxytocin/vasopressin-like peptide identified in Daphnia culex and with a novel form of oxytocin described in New World monkeys. The expression of pro-sepiatocin is restricted to the supraesophageal and subesophageal masses of the brain whereas sepiatocin is expressed in the entire central nervous system. Sepiatocin, as described for octopressin, modulates the contractile activity of several muscles such as penis, oviduct and vena cava muscles; this suggests its involvement in reproduction and blood circulation. Pro-sepiatocin is released in the hemolymph; it is a neurohormone able to target numerous peripheral organs.