gene is an excellent candidate molecular marker for studying primordial germ cells because of its specific expression in germ cell lineages. PGCs can be labeled by a reporter gene driven by regulatory regions of the ) is an economically important flatfish in China, and the females of this species grow two to four times bigger than males. Sex reversal is common in this fish and females cannot guarantee egg production by natural spawning under artificial culture conditions. Therefore, transplantation of PGCs and surrogate broodstock production might be employed to improve the production of this fish. Promoter choice in transgenic research is important for regulating expression of a foreign gene. However, the function of ) regulatory regions in tongue sole remains unknown. We aimed to isolate the regulatory regions of the gene, examine its transcriptional activity in transgenic medaka fish, and identify the conditions required for manipulation of PGCs. Two DNA fragments, including a 5166-bp 5′ region and a 1655-bp 3′ region, were obtained by genome walking and polymerase chain reaction of genomic DNA. The 5′ region of contains the major promoter region, exon 1, intron 1 and exon 2. The transcription initiation site and a putative TATA box were identified and potential transcription factor binding sites were bioinformatically analyzed. Several potential transcription factor binding sites that may perform important function relating to gene transcription, such as SRY, Oct-1, Sox-5, CREB, GATA, AP-1, C/EBP, Sp-1, c-Myc, HNF, NKX2-5, and V-Myb were predicted. Based on the above information, the regulatory regions were inserted into a pEGFP-N3 vector lacking the CMV promoter. This vector expresses the green fluorescent protein(GFP). The recombinant p-GFP-T plasmid was injected into medaka fertilized eggs by microinjection. Microfluoroscopy revealed that the level of expression was 81% in the injected embryos. GFP-fluorescent medaka embryos were cultured to adult fish and the integration efficiencyof pCsvasa promoter can efficiently drive expression in medaka embryos, and lay the foundations for identifying, labeling and tracing PGCs, investigating germ cell biology, and manipulating the sex of half-smooth tongue sole.