Specification of sense-organ identity by a Caenorhabditis elegans Pax-6 homologue

The Pax-6 transcription-factor gene, containing a paired domain and a paired-type homeodomain, is conserved in structure and ubiquitously present among Metazoa. It is required for development of the central nervous system, and is mutated in human aniridia, mouse and rat small eye and Drosophila eyeless. We identified the Pax-6 gene of the nematode Caenorhabditis elegans in genetic studies of male tail morphology. C. elegans Pax-6 encodes at least two independent genetic functions. One, like other Pax-6 genes, contains paired and homeodomains; this constitutes the genetic locus vab-3. The other, described here, is expressed from an internal promoter and contains only the homeodomain portion; this constitutes the genetic locus mab-18. The mab-18 form of the gene is expressed in a peripheral sense organ and is necessary for specification of sense-organ identity. Its function in this context could be to regulate the expression of cell recognition and adhesion proteins required for sense-organ assembly.