Germ cell-specific expression of green fluorescent protein in transgenic rainbow trout under control of the rainbow trout vasa-like gene promoter

A technique to identify a nd isolate live fish primordial germ cells (PGCs) has not been established, in spite of the importance of purified germ cell s for molecular and cellular studies. In rainbow trout, the distribution of vasatranscripts is restricted to the germ cell lineage, making this transc ript a useful indicator of PGCs. Therefore, in this study, we cloned and ch aracterized the rainbow trout vasa-like gene (RtVLG) regulatory regions and produced transgenic trout carrying the green fluorescent protein (GFP) gen e driven by the RtVLG regulatory regions (pvasa-GFP) in order to identify l ive PGCs in vivo. In transgenic trout carrying the pvasa-GFP construct, cel ls showing green fluorescence were first observed at the mid-blastula stage ; however, no cell-type-specific expression was observed at this stage. At the eyed stage, about 30% of the transgenic embryos showed specific GFP exp ression in PGCs, and at the hatching stage, about 70% of the transgenic emb ryos did so. An immunohistochemical study of hatching stage embryos reveale d that the GFP-expressing cells are located in genital ridges. This transge nic trout, having visualizable PGCs, will make it possible to isolate live PGCs for in vitro studies and to study the ontogeny of PGCs including sex d ifferentiation in live embryos.