Patterning of the Caenorhabditis elegans head region by the Pax-6 family member vab-3

The Pax-6 genes are important for eye development in both vertebrates and Drosophila. Mutations in the human PAX6 gene are found in patients with a variety of eye disorders, including aniridia and Peters' anomaly, and mutations in the Drosophila Pax-6 homologue cause the eyeless phenotype. In the nematode Caenorhabditis elegans, vab-3 mutants display many defects in head-region development, including aberrant morphogenesis, transformation of hypodermal (epidermal-like) cell fates to those of posterior homologues, and abnormal specification of neurons. Here we show that vab-3 is a member of the paired-domain-containing Pax-6 gene family and is expressed in head-region cells. This C. elegans Pax-6 locus can also encode proteins lacking the paired domain. Our results suggest that a primordial role of the Pax-6 gene family could have been to pattern part of the head region, and that Pax-6 genes subsequently evolved to be more specifically involved in eye development.