ISOLATION OF A PAX-6 HOMOLOG FROM THE RIBBONWORM LINEUS-SANGUINEUS

The Pax-6 genes of vertebrates and Drosophila encode transcription fac tors with highly conserved paired- and homeodomains. They are expresse d in the nervous system and the developing eyes. Loss of-function muta tions in mammals and flies lead to a reduction or absence of the eyes, By ectopic expression of Pax-6 in Drosophila ectopic eyes can be indu ced, indicating a determinative role in eye morphogenesis. We have iso lated a Pax-6 homolog of the ribbonworm Lineus sanguineus. This gene s hares extensive sequence identity and several conserved splice sites w ith the mammalian and Drosophila genes. During head regeneration the L . sanguineus Pax-6 homolog is expressed in the central nervous system, in the cerebral organ, and in the eye region. These findings support the hypothesis that Pax-6 was present in primitive metazoa before the evolutionary separation of vertebrates and arthropods and suggest a fu ndamental role in eye and central nervous system development.