|Budget Amount *help
¥2,800,000 (Direct Cost : ¥2,800,000)
Fiscal Year 2000 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1999 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1998 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1997 : ¥1,000,000 (Direct Cost : ¥1,000,000)
In order to know the fundamental genetic steps in the formation of brain in vertebrates, we investigated the neural tube mutants in the medaka (Oryzias latipes). Small-scale mutagenesis using ENU (N-nitroso-N-ethylurea) or X-rays followed by three-generation crosses was carried out. The chemically induced mutations could be recovered efficiently in the medaka, indicating that the medaka is a suitable vertebrate for use in large-scale mutagenesis. We obtained about 90 medaka mutant strains in total. All mutations were zygotic recessive except for two. Eighteen of the 90 mutations displayed abnormalities in the formation of neural tube. These included novel brain phenotypes, such as Oot, act, gac, nnc, hit, hir, and htl. For example, in the Oot (One-sided optic tectum) phenotypes, bilateral symmetry was broken in the optic tectum in the early developmental stage, and either the left or right morphology was duplicated on both sides. This phenotype of the brain mutants has never been reported so far in other vertebrates including zebrafish. Hence, our results indicate that, in the medaka, it is possible to identify mutations, the phenotypes of which could not be found in zebrafish mutants obtained by large-scale mutagenesis. It seems hopeful that genetic steps that are important in the formation of the neural tube can be clarified through the studies of these medaka mutations.