Zebrafish contains two Pax6 genes involved in eye development

The Pax6 genes of both vertebrates and invertebrates are expressed in the d eveloping eye and in the central nervous system. These genes encode transcr iption factors with two DNA-binding domains, an N-terminal paired domain an d a homeodomain separated by a flexible linker region. Ectopic eye structur es are obtained upon targeted expression of Drosophila, squid, ascidian or mouse Pax6 genes in various imaginal disc primordia of Drosophila. We have previously cloned a Pax6 cDNA from zebrafish. Here we report the cloning of a novel Pax6 homolog from zebrafish denoted Pax6.2. The coding sequences o f the two genes show 82% identity whereas the deduced amino acid sequences are 95% identical with complete conservation of the paired- and homeodomain s. The embryonic expression patterns of Pax6.1 and Pax6.2 reveal both overl apping and discrete expression domains suggesting a division of labor betwe en these two very similar gene products during development of brain and eye structures. Both Pax6.1 and Pax6.2 can act as transcriptional activators w ith Pax6.2 being more efficient than Pax6.1. Both Pax6.1 and Pax6.2 are abl e to induce ectopic eyes in Drosophila, while Pax2 is not, suggesting that eye induction is not a general feature of. Pax family genes but a distinct characteristic of Pax6 and its direct homologs. Attempts to detect Pax6. 2 homologs in chick, mice or humans proved unsuccessful suggesting that this gene either was lost during evolution of higher vertebrates or, more likely , arose as part of a larger scale duplication of chromosome segments occurr ing in the zebrafish lineage. (C) 1998 Elsevier Science Ireland Ltd. All ri ghts reserved.