Regulation of Eye Determination and Regionalization in the Spider .

Animal visual systems are enormously diverse, but their development appears to be controlled by a set of conserved retinal determination genes (RDGs). Spiders are particular masters of visual system innovation, and offer an excellent opportunity to study the evolution of animal eyes. Several RDGs have been identified in spider eye primordia, but their interactions and regulation remain unclear. From our knowledge of RDG network regulation in , we hypothesize that orthologs of , , Wnt genes, , , and could play important roles in controlling eye development in spiders. We analyzed the expression of these genes in developing embryos of the spider , both independently and in relation to the eye primordia, marked using probes for the RDG . Our results support conserved roles for Wnt genes in restricting the size and position of the eye field, as well as for initiating photoreceptor differentiation. However, we found no strong evidence for an upstream role of in eye development, despite its label as a master regulator of animal eye development; nor do , or compensate for the absence of . Conversely, our results indicate that may work with Wnt signaling to restrict eye growth, a role similar to that of () in vertebrates.