Analysis of developmental genetic system using small teleost fish as vertebrate model systems

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In the present study, we focused on the medaka that became an attractive model organism for the study of vertebrate early development and genome evolution. The following three groups were jointed, aiming at the establishment of comprehensive resources for medaka developmental genetics as well as structural and functional analyses of developmentally important genes in medaka.1. Takeda and NaruseTo strengthen the study of medaka developmental genetics, Takeda's laboratory has conducted a large-scale isolation of ESTs from medaka embryos and developed tools that facilitate mutant analysis such as rapid mapping system, M-markers and microarray with 8,000 uni-genes. These resources are accelerating medaka mutant analyses and made an important contribution to the medaka genome sequencing project.2. HoriHori's laboratory analyzed the organization of the entire hox gene loci. Together with the information in the Fugu genome database and in the Danio genome database, the physical maps of three fish genomes were constructed and compared one another. Not only numbers of hox genes but also the distances between the neighboring hox genes are highly similar between medaka and fugu. As for six clusters, Aa, Ab, Ba, Bb, Ca and Da that are commonly present in the three fishes, only few or no differences were found in each cluster. Thus, the hox gene sets should have been well conserved once they had been established in respective species.3. KudoKudo's laboratory has screened for mutants that are defective in organogenesis and fin regeneration in the medaka, using ethylnitrosourea (ENU) as a mutagen. A total of 386 mutagenized genomes were scored to identify 151 mutations affecting organogenesis, and 16 mutations affecting the fin regeneration were identified. In parallel, they isolated 20,000 ESTs from re-generating fins, representing about 3,000 uni-genes.