The ziwi promoter drives germline-specific gene expression in zebrafish

We describe here the characterization of the promoter activity of a 4.8-kb sequence isolated from the 5' end of the zebrafish germ cell-specific ziwi gene. We show that this fragment is sufficient to drive heterologous gene expression specifically in germ cell starting as early as 7 days post-fertilization, a time point when only mitotic germ cells are present in the gonad. In adult animals, we find that this fragment is sufficient to drive gene expression in all germ cells with stage-specific differences in expression levels. In females, EGFP expression is highest in stage IB oocytes, but appreciable expression is detected in both pre-meiotic germ cells, as well stage II-IV oocytes and mature eggs. In males, EGFP expression is highest in spermatogonial stem cells, but low levels are detected in all stages, including spermatozoa.