Evolutionary implication of the absence of atrial natriuretic peptide (ANP) in euryhaline Oryzias fishes

Koji Inoue, Hiroshi Miyanishi, Shigenori Nobata, Yoshio Takei

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


The genus Oryzias contains nearly 20 species, including the Japanese medaka (Oryzias latipes). Because each species exhibits different adaptability to environmental salinity, Oryzias fishes offer unique opportunities for comparative studies. To understand the mechanisms of osmotic adaptation, we are studying the functional evolution of the natriuretic peptide (NP) family-a group of small peptide hormones involved in body fluid regulation-by using Oryzias fishes. Analysis of the Japanese medaka genome revealed that 7 NP subtypes, namely, Atrial NP (ANP), B-type NP (BNP), Ventricular NP (VNP), and 4 C-type NPs (CNP-1 through CNP-4) were generated from a CNP-4-like ancestral gene discovered in the cyclostomes before the ray-finned fish/lobe-finned fish divergence. This evolutionary history has been confirmed by the discovery of hidden NP genes in tetrapods. Through analyses of phylogenetic distribution of NP subtypes, we also found that specific losses of subtypes have occurred in each vertebrate lineage. For example, ANP is absent in the Japanese and Indian medaka and the flying fish, suggesting that loss of the ANP gene occurred after the divergence of Beloniformes from Cyprinodontiformes. This fact also supports the inclusion of Oryzias into Beloniformes as suggested by phylogenetic analysis using whole mitochondrial genome sequences. How Oryzias fishes have retained their euryhalinity with a reduced number of NPs is an interesting question. CNP-3, which is functionally flexible, may be a substitute for the lost cardiac NPs.

Original languageEnglish
Pages (from-to)559-566
Number of pages8
JournalEnvironmental Biology of Fishes
Issue number3
Publication statusPublished - 2012 Jul


  • ANP
  • BNP
  • Beloniformes
  • Medaka
  • Natriuretic peptides
  • Osmoregulation

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science


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