Medaka is an excellent experimental model animal
We use Japanese medaka (Oryzias latipes), a small aqueous fish which inhabits Japan, as an experimental model animal. Because medaka is a vertebrate, it reflects many aspects of humans better than prokaryotes such as E. coli, and invertebrates such as worm and fly. The genome information and bioresource is now available with the advance of technology and the governmental support. The advantage of using medakas in research over using rodent models such as mice and rats is as follows:
Easy to raise and handle. Requires little space and cost.
Sexually maturates within two months.
High fecundity, which means they produce many eggs. The experiments can be easily scaled up.
Develops ex vivo, which makes the detailed analysis possible during embryogenesis.
The gene expression levels can be easily altered by microinjection of transgene or antisense oligonucleotide into eggs.
The embryos are transparent, making live imaging possible with the use of GFP, etc.
Can be treated with mutagenic substances to create animals with point mutations.
Easy to conduct cryopreservation and artificial insemination.
Suitable for the drug screening in multi-well plates due to the small size.
The following features of medakas are especially important in the study of ecotoxicology.
Fish are predator in the food chain. Toxic chemicals can accumulate in the fish body.
Fish are eaten by human beings, thus directly affecting our health.
Fish belong to vertebrae, and reflect at least some aspects of metabolic pathways of humans.
We can observe fish not only from the outside but from the inside as well.
The effect of chemicals on embryogenesis can be assessed easily.
The number of samples can be increased easily.
Zebrafish (Danio rerio) is another aqueous fish that are used as a model animal. They are more popular than medakas, and much robust bioresouｒｃe has been established that provides researchers with mutants, cDNAs, and integrated information from literature. Zebrafish lay more eggs, and the embryos develop much faster than medakas. Despite all these advantages of zebrafish, we chose medakas as a experimental model due to the following features.
They are hardier than zebrafish.
Tolerates a wide range of temperature.
Tolerates a wide range of salt concentration.
Genetically homogenous inbred strains are available.
Sex chromosome and the sex-determination gene have been identified.
Easier to conduct cryopreservation and artificial insemination.
Long history of research in Japan.
Has more compact genome than zebrafish.
The genome project has been completed.
The gene disruption by TILLING is easier.。
