Specification of sensory organ identity by a Caenorhabditis elegans Pax-6 homolog

Abstract

During development, different cells and tissues have to be specified to generate structural and functional diversity. The specification of sensory rays on the male tail of C. elegans has been used as a model system to study this question. In particular, the specification of ray 6, a ray that is uniquely thick and tapered in shape, was analyzed on a cellular and molecular level.;Each sensory ray comprises three cell processes that originate from three different cells: two neuronal cells and one structural cell. The structural cell is a support cell that functions as both sheath and socket cells found in other sensory organs. By laser ablation of individual cells, I have shown that structural cells confer ray architecture as well as the properties that distinguish rays from each other. In contrast, the two neuronal cells are not required in the production of ray architecture or properties. In mab-18 mutants, the specific properties of the ray 6 structural cell that make ray 6 thick are transformed to that of an anterior ray. mab-18 was found to encode a protein containing a highly conserved homeodomain similar to that of the vertebrate gene Pax-6 and the Drosophila gene eyeless. Reporter gene studies suggest that mab-18 acts cell autonomously to specify the ray 6 morphology and location in the hypodermis. This demonstration of Pax-6 in the specification of ray properties in this primitive worm suggests that Pax-6 was an ancient gene and its general function would be to specify the nervous system. The expression of mab-18 is also shown to be under the control of genes belong to the Hox cluster and genes in the TGF-{dollar}\beta{dollar} pathway.