Generation of oocyte-specifically expressed cre transgenic zebrafish for female germline excision of loxP-flanked transgene.

In this communication, we report the generation of a cre transgenic zebrafish line under an oocyte-specific promoter, zp3. The transgenic line Tg(zp3:cre; krt8:rfp) also contains a co-integrated rfp transgene under the skin epithelial promoter krt8 to allow selection of cre transgenic fish based on RFP fluorescence in the skin. We demonstrated in this transgenic line that cre mRNA was specifically expressed in growing oocytes like endogenous zp3 mRNA. When Tg(zp3:cre; krt8:rfp) was crossed with a loxP transgenic line, the floxed DNA was specifically eliminated from female, but not male, germline. Tg(zp3:cre; krt8:rfp) fish also have maternal cre mRNA in early embryos to cause Cre-mediated recombination; this feature can be used to activate other loxP transgenic lines in early embryos. Furthermore, after crossing with another loxP transgenic line, Tg(EF:loxP-mCherry-loxP-egfp), we confirmed that our cre line was capable of activating a loxP-blocked EGFP reporter gene by both maternal and oocyte-expressed Cre.