Zebrafish transgenic lines co-expressing a hybrid Gal4 activator and eGFP in tissue-restricted patterns.

We have used a Tol2-derived trapping vector, carrying a hybrid Gal4 gene and a UAS:eGFP reporter cassette, to identify 16 transgenic zebrafish lines expressing the fluorescent marker eGFP in tissue-restricted patterns during development. Most lines show co-expression of eGFP and a hybrid Gal4 transcription activator containing a truncated VP16 domain that facilitate induction of other UAS-transgenes (UAS:RFP). Notably, many of the transgenic lines are expressed in particular areas of the central nervous system, such as the retina. We mapped the genomic positions of most of the activated insertions, and for three retina-specific lines we also demonstrate that eGFP reports the expression of particular endogenous genes. One of the identified zebrafish genes shows expression in ventral retina, and encodes a protein containing a repulsive guidance molecule (RGM) domain, suggesting a role in axonal guidance during optic nerve formation. Among the lines labeling other tissues, three show early co-expression of eGFP and Gal4-VP16 in blood vessels, erythrocytes and other hematopoietic cells. Interestingly, the activated insertion in the erythrocyte line was mapped to a site near the globin cluster on chromosome 3. All the reported lines co-expressing eGFP and the hybrid Gal4 activator may have potential as genetic tools to study developmental processes.