Investigation for Common Molecular Mechanisms by Comparison of EST from Purified Germ Cells

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medaka embryos are transparent, which allows us to monitor the development process occuring in morphogenesis in vivo. We have developed transgenic medaka using the regulatory regions of germline-specific expressed gene, vasa, fused with the green fluorescent gene. With this transgenics, we can observe the development of germline, the cell lineage for the future eggs or sperms. We have established the skills for isolating several germ cells and generated cDNA libraries for ESTs expressed exclusively in germline.Our initial purpose was to compare the medaka ESTs with mouse germline ESTs to reveal the genes commonly expressed beyond the species. We could not generate the libraries good enough for representing medaka germline ESTs. However, among the thousnads of ESTs we sequenced, several interesting ESTs have been found. By the expression and functional analyses of the ESTs, we successfully kept track of germline from fertilized eggs. Medaka germline is detected at the gastrulation stage, which has been suggesting that development of germline is similar to that seen in mammals. Our results indicate that germline development is more likely to that of other vertebrates where germline can be marked by specific cellular structures. Furthermore we demonstrated thatgermline goes through three steps of developmental process with three different modes of migration towards gonadal area.