Purpose. Pax-6 in vertebrates and its homologue eyeless in Drosophila are known to be absolutely essential for early eye development. We systematic group - cephalopod molluses. Methods. Using PCR approach full length cDNA encoding squid Pax-6 was isolated from squid embryos. Northern and in situ hybridization. Full length squid Pax-6 cDNA was ectopically expressed in Drosophila by means of the GAL4 system. Results. Squid Pax-6 is encoded by a single gene which is alternatively spliced at the 5′ end exactly in the same place where alternative splicing was observed in the Drosophila eyeless gene. One of the presumably complete versions of Pax-6 is 459 amino acids long. It shows 92-96% and 90-95% identities with the vertebrate and Drosophila homologues in paired- and homeodomain regions, respectively. Pax-6 is actively expressed in embryonic squid but not in adult tissues tested (lens, cornea, total eye, optic lobe). In situ hybridization experiments demonstrated that Pax-6 is expressed in embryonic eyes, in the region of future cornea and iris, but not in the lentigenic cells, where S-crystallin genes were actively expressed. Full length squid Pax-6 was able to induce ectopic eyes on the wing of Drosophila. All Drosophila eye-specific structures including cornea, pigment cells, cone cells and photoreceptors with rhabdomeres were formed. Conclusions. The results suggest that Pax-6 plays an essential role in eye development of cephalopods as it does in vertebrates and insects.
