Positive and negative regulatory inputs restrict pax-6/vab-3 transcription to sensory organ precursors in Caenorhabditis elegans

The Pax-6 gene encodes a transcription factor essential for the development of eyes and other sensory organs in species ranging from planaria to mice. Because Pax-6 activity can be both necessary and sufficient for eye organogenesis, much work has focused on PAX-6 function and regulation of target genes. However, less is known about the genetic mechanisms that establish the Pax-6 expression pattern. We have utilized Caenorhabditis elegans as a relatively simple model system to characterize the regulation of Pax-6 transcription in sensory organ precursors. In C. elegans males, two sensory mating structures, the copulatory spicules and the post-cloacal sensilla, are formed from stereotyped divisions of the two post-embryonic blast cells, B.a and Y.p, respectively. A C. elegans pax-6 transcript, vab-3, is necessary for the development of these sensory structures. Using a green fluorescent protein (GFP)-based vab-3 transcriptional reporter, we show that expression is restricted to the sensory organ lineages of B.a and Y.p. Transcription of vab-3 in the tail region of the worm requires the Abdominal B homeobox gene, egl-5. Opposing this activation, a transcription factor cascade and a Wnt signaling pathway each act to restrict vab-3 expression to the appropriate cell lineages. Thus we have identified multiple genetic pathways that act to restrict pax-6/vab-3 gene expression to the sensory organ precursor cells.