COMPARATIVE-ANALYSIS OF PAX-6 SEQUENCE AND EXPRESSION IN THE EYE DEVELOPMENT OF THE BLIND CAVE FISH ASTYANAX-FASCIATUS AND ITS EPIGEAN CONSPECIFIC

The Pax-6 gene encodes a transcription factor essential for eye develo pment in a wide range of animal phyla. In order to elucidate a possibl e role of Pax-6 in the eye regression of a blind cave form of the fres hwater fish Astyanax fasciatus (Characidae, Teleostei) we investigated the expression of Pax-6 in eyes and brains of different larval stages by in situ hybridization. Pattern, strength, and time course of Pax-6 expression were not altered in the tissues of the cave form when comp ared to the epigean form. Pax-6 was even expressed in the highly degen erated eyes of late larval stages of the cave form. Comparative sequen ce analysis of Pax-6 cDNA clones of both forms of Astyanax fasciatus s howed the complete integrity of cave fish Pax-6 mRNA. These results su ggest that Pax-6 is not involved in the evolutionary process of eye de generation in this model system of cave-living fishes. Comparison of t he Astyanax Pax-6 cDNA with the other available fish Pax-6 sequence fr om zebrafish revealed putative fish-specific regions of homology. A st retch of 19 N-terminal amino acids is nearly identical on the nucleoti de and amino acid levels in both fish species but not present in all o ther known Pax-6 sequences.