SEQUENCE-ANALYSIS OF VASOTOCIN CDNAS OF THE LAMPREY, LAMPETRA-JAPONICA, AND THE HAGFISH, EPTATRETUS-BURGERI - EVOLUTION OF CYCLOSTOME VASOTOCIN PRECURSORS

We determined the nucleotide sequences of cDNAs encoding precursors of vasotocin (VT) from two cyclostomes, the lamprey Lampetra japonica an d the hagfish Eptatretus burgeri, for estimation of their phylogenetic relationships. Although only 47% similarity was found between the VT cDNAs, the predicted VT precursors of the lamprey and the hagfish were both composed of a signal peptide, VT, Gly-Lys-Arg and a neurophysin, as has been shown for precursors of vasopressin (VP) family hormones, including VP, VT and molluscan conopressin. The central region of the lamprey neurophysin was very similar to those of previously character ized gnathostome neurophysins. Conspicuously, all the positions of 14 Cys residues were conserved in the lamprey neurophysin. The C-terminal region did not have a distinctive Leu-rich core segment, which is alw ays found in the glycopeptide (copeptin) moiety of VP precursors. In c ontrast, the hagfish neurophysin showed at least two insertions and on e deletion in the conserved central region including 14 Cys residues, but contained a potential N-linked glycosylation site and had a high p roportion of Leu residues in the C-terminal region, like the neurophys in of another hagfrsh, Eptatretus stouti. The evolutionary relationshi ps of the precursors of VP family hormones among the lamprey, hagfish, gnathostomes and a mollusc were estimated by a maximum likelihood met hod. The phylogenetic tree with the highest bootstrap probability show ed that the lamprey VT precursor is more closely related to the gnatho stome VT and VP precursors than to the hagfish VT precursors.