Abstract
BackgroundThe genome sequence of the pufferfish Takifugu rubripes is an enormously useful tool in the molecular physiology of fish. Euryhaline fish that can survive both in freshwater (FW) and seawater (SW) are also very useful for studying fish physiology, especially osmoregulation. Recently we learned that there is a pufferfish, Takifugu obscurus, common name "mefugu" that migrates into FW to spawn. If T. obscurus is indeed a euryhaline fish and shares a high sequence homology with T. rubripes, it will become a superior animal model for studying the mechanism of osmoregulation. We have therefore determined its euryhalinity and phylogenetic relationship to the members of the Takifugu family.ResultsThe following six Takifugu species were used for the analyses: T. obscurus, T. rubripes, T. niphobles, T. pardalis, T. poecilonotus, and T. porphyreus. When transferred to FW, only T. obscurus could survive while the others could not survive more than ten days in FW. During this course of FW adaptation, serum Na+ concentration of T. obscurus decreased only slightly, but a rapid and large decrease occurred even in the case of T. niphobles, a peripheral fresh water species that is often seen in brackish river mouths. Phylogenetic analysis using nucleotide sequences of the mitochondrial 16S ribosomal RNA gene of each species indicated that the six Takifugu species are very closely related with each other.ConclusionT. obscurus is capable of adapting to both FW and SW. Its genomic sequence shares a very high homology with those of the other Takifugu species such that the existing Takifugu genomic information resources can be utilized. These properties make "mefugu", which has drawn little attention from animal physiologists until this study, a useful model animal for studying the molecular mechanism of maintaining body fluid homeostasis.
Highlights
The genome sequence of the pufferfish Takifugu rubripes is an enormously useful tool in the molecular physiology of fish
We focus on the suitability of T. obscurus as a novel animal model for studying the molecular mechanism of body fluid homeostasis
These data suggest that only T. obscurus is fully adaptable to both FW and SW among the six Takifugu species tested
Summary
Survival of Takifugu species in FW A summary on six Takifugu species used in this study is shown in Figure 1 and Table 1. Our preliminary results of the nucleotide sequences of several cDNA clones for ion transporters (Na+/H+ exchangers; accession numbers AB200326–AB200333) and hormone receptors (members of the adrenomedullin receptor family: accession numbers AB219765– AB219771, AB219835–AB219840) [21] of T. obscurus were 99% identical to those of T. rubripes including the non-coding sequences (data not shown). These results suggest that the Takifugu species diversified very recently and the genome resources of T. rubripes can be used for studying the T. obscurus genes and their products
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