Medaka, Oryzias latipes
(Order Beloniformes), is a small, egg-laying freshwater teleost fish found in the brooks and rice paddies of China, Korea and Japan. This fish has been developed as a research material (Aida, T., 1921; Yamamoto, T., 1953; For reviews
see Shima, A. and Mitani, H., 2004; Naruse K., et al 2004; Furutani-Seiki, M. and Wittbrodt J., 2004) in Japan and is now widely used in various research fields including biology, medical science and environmental science. Furthermore, a large scale ENU mutagenesis screening has been performed and identified more than 300 mutants with defects in organogenesis. A draft level genome sequence and more than 30,000 unique gene/EST sequences (DFCI Medaka Gene Index
) and BAC/Fosmid
clones are available. Medaka has the largest genetic variation (an average of 4%) in vertebrate species so far and these variations are clearly correlated with geographical distribution
. This is a distinctive characteristic compared with other model vertebrates like zebrafish. Furthermore, several inbred strains which represent each regional population have also been established. Alternative vertebrate models with these features are not available.
Comparative genomic study among medaka and other vertebrates clearly showed that the synteny among teleosts was strongly conserved on the chromosomal level and even between the teleosts and mammals
, and that they shared many common genomic features including the mechanism of development and organogenesis and gene expression machineries. From the evolutionary point of view, the molecular phylogenetic analysis of the natural population of medaka
and medaka-related species
allows for new perspectives of the natural environment of East and South-East Asia and the establishment of fish fauna in Asia.
Along with the development and collection of strains, several methods related to embryo manipulation and gene manipulation including the generation of transgenics and visualization technology with single cell level have also been developed.
Thus, all of these unique features have allowed medaka to be established as the representative "model vertebrate" system for analyzing a variety of biological phenomena.
In the second term of National BioResource Project (NBRP) Medaka, three organizations - the National Institute for Basic Biology (Core Institute), Niigata University, and the National Institute of Radiological Sciences - were appointed at the 2006 meeting ( NBRP genetic resources committee for medaka ) to efficiently provide, maintain and collect living and frozen medaka resources and the integrated information on medaka with the goal of facilitating and enhancing the use of medaka as a model organism.
The living resources include standard strains, wild stocks, inbred strains, medaka-related species and spontaneous and induced mutants. In addition to these live resources, the BAC/Fosmid clones will be provided, which cover 90 % of medaka genome and over 15,000 non-redundant EST clones. NBRP Medaka serves to develop, support and update the latest genetic and biological information, including genomic data (genome sequences, transcription initiation site (TSS) and predicated genes).
Thus, NBRP Medaka is aiming to establish a first rate biological resource with the highest possible levels of accessibility and ease of use .