|Budget Amount *help
¥3,200,000 (Direct Cost : ¥3,200,000)
Fiscal Year 2004 : ¥1,400,000 (Direct Cost : ¥1,400,000)
Fiscal Year 2003 : ¥1,800,000 (Direct Cost : ¥1,800,000)
In this study, I studied mechanism of immediate regulation of the body fluid osmolality in fish against sudden changes in salinity of environmental water. Studies were focused on three peptide hormone families, the natriuretic peptide (NP) family, guanylin (GN) family and adrenomedullin (AM) family. As for NP family, I and collaborators found seven NP subtypes exist in fish whereas only three subtypes have been found in mammals. By comparative genomic analysis, among the medaka, pufferfishes and human, and linkage mapping in the medaka and rainbow trout, we found that the NP family has been generated through two steps : one is the chromosomal duplications that generated four NP sgenes from a single ancestral gene and the other is tandem duplications that generated additional three genes from one of the four NP genes. As for GN family, we found three ligands and two receptors in the eel whereas mammals have two ligands and one receptor. We also showed that the expression levels of the three ligand genes are higher in seawater than in fresh water in the eel. As for AM family, we found five genes from the pufferfish whereas only one gene has been found in mammals. Using the sequence and genomic information in the pufferfish, we successfully found a new hormone, AM2 from mammals including human and mouse. In addition, we have been attempted to establish a new experimental model for osmotic adaptation studies. We found a catadromous cottid fish, Cottus kazika should be a good model.