Evidence for conservation of the vasopressin/oxytocin superfamily in annelida

Annetocin is a structurally and functionally oxytocin-related peptide isola ted from the earthworm Eisenia foetida. We present the characterization of the annetocin cDNA. Sequence analyses of the deduced precursor polypeptide revealed that the annetocin precursor is composed of three segments: a sign al peptide, an annetocin sequence flanked by a Gly C-terminal amidation sig nal and a Lys-Arg dibasic processing site, and a neurophysin domain, simila r to other oxytocin family precursors. The proannetocin showed 37.4-45.8% a mino acid homology to other prohormones. In the neurophysin domain, 14 cyst eines and amino acid residues essential for association of a neurophysin wi th a vasopressin/oxytocin superfamily peptide were conserved, suggesting th at the Eisenia neurophysin can bind to annetocin. Furthermore, in situ hybr idization experiments demonstrated that the annetocin gene is expressed exc lusively in neurons of the central nervous system predicted to be involved in regulation of reproductive behavior. These findings confirm that annetoc in is a member of the vasopressin/oxytocin superfamily. This is the first i dentification of the cDNA encoding the precursor of an invertebrate oxytoci n-related peptide and also the first report of the identification of an ann elid vasopressin/oxytocin-related precursor.