Australian lungfish neurohypophysial hormone genes encode vasotocin and [Phe2]mesotocin precursors homologous to tetrapod-type precursors

Susumu Hyodo*, Susumu Ishii, Jean M P Joss

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)

Abstract

In view of the well-established role of neurohypophysial hormones in osmoregulation of terrestrial vertebrates, lungfishes are a key group for study of the molecular and functional evolution of the hypothalamo- neurohypophysial system. Here we report on the primary structure of the precursors encoding vasotocin (VT) and [Phe2]mesotocin ([Phe2]MT) of the Australian lungfish, Neoceratodus forsteri. Genomic sequence analysis and Northern blot analysis confirmed that [Phe2]MT is a native oxytocin family peptide in the Australian lungfish, although it has been reported that the lungfish neurohypophysis contains MT. The VT precursor consists of u signal peptide, VT, that is connected to a neurophysin by a Gly-Lys-Arg sequence, and a copeptin moiety that includes a Leu-rich core segment and a glycosylation site. In contrast, the [Phe2]MT precursor does not contain a copeptin moiety. These structural features of the lungfish precursors are consistent with those in tetrapods, but different from those in teleosts where both VT and isotocin precursors contain a copeptin-like moiety without a glycosylation site at the carboxyl terminals of their neurophysins. Comparison of the exon/intron organization also supports homology of the lungfish [Phe2]MT gene with tetrapod oxytocin/MT genes, rather than with teleost isotocin genes. Moreover, molecular phylogenetic analysis shows that neurohypophysial hormone genes of the lungfish are closely related to those of the toad. The present results along with previous morphological findings indicate that the hypothalamo-neurohypophysial system of the lungfish has evolved along the tetrapod lineage, whereas the teleosts form a separate lineage, both within the class Osteichthyes.

Original languageEnglish
Pages (from-to)13339-13344
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume94
Issue number24
DOIs
Publication statusPublished - 25 Nov 1997

Keywords

  • Molecular cloning
  • Molecular evolution
  • Phylogenetic tree
  • Precursor organization

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