Natriuretic peptides govern euryhalinity of fishes Analyses using transgenid technology

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Accumulating data from this laboratory strongly indicate that the natriuretic peptides (NPs) govern euryhalinity of eels ; atrial NP (ANP) promotes seawater adaptation and C-type NP (CNP) promotes freshwater adaptation. In this study, we attempted to determine that ANP is in fact essential for seawater adaptation using transgenic techniques. For this purpose, we use medaka fish that have plural akin species in the same genus that exhibit diverse osmotic adaptability and in which transgenic technique has already been established. Therefore, the production of ANP transgenic seawater medaka that cannot survive in seawater without transferred ANP gene will directly demonstrate the importance of ANP in seawater adaptation. However, ANP cDNA have not been cloned in medaka fish although cloning was successful in several other teleost species. Meanwhile, we could detect four CNPs, named CNP-1 through 4, and B-type NP (BNP) that had been thought as tetrapod-specific NP. Furthermore, we isolated CNP-4 type NPs from most primitive extant vertebrates, lamprey and hagfish. Therefore, we proposed new hypothesis of the molecular evolution of the NP family ; CNP-4 is an ancestral molecule of the NP family and it was diversified in bony fishes in parallel with the evolution of osmoregulatory mechanisms.