Abstract
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 Drosophila melanogaster, we hypothesize that orthologs of Pax6, eyegone, Wnt genes, hh, dpp, and atonal could play important roles in controlling eye development in spiders. We analyzed the expression of these genes in developing embryos of the spider Parasteatoda tepidariorum, both independently and in relation to the eye primordia, marked using probes for the RDG sine oculis. Our results support conserved roles for Wnt genes in restricting the size and position of the eye field, as well as for atonal initiating photoreceptor differentiation. However, we found no strong evidence for an upstream role of Pax6 in eye development, despite its label as a master regulator of animal eye development; nor do eyg, hh or dpp compensate for the absence of Pax6. Conversely, our results indicate that hh may work with Wnt signaling to restrict eye growth, a role similar to that of Sonic hedgehog (Shh) in vertebrates.
Highlights
Spiders have some of the most diverse visual systems in the animal kingdom [1].They exhibit substantial variation on a conserved anatomical blueprint, including eye size, arrangement, function, and even number (Figure 1A)
To address whether Pax6 genes could play a role in spider eye development, we performed a detailed expression pattern analysis of the two Pax6 paralogs of P. tepidariorum, using Pt-so1 as a marker of the developing eye primordia
Expression is split into two domains, corresponding to the positions of the principal and secondary eye primordia, but is quite diffuse
Summary
Spiders have some of the most diverse visual systems in the animal kingdom [1]. They exhibit substantial variation on a conserved anatomical blueprint, including eye size, arrangement, function, and even number (Figure 1A). Despite there being more than 40 estimated evolutionary origins of vision [3], studies of eye development across the animal kingdom have consistently found a core set of genes that determine eye fate, including members of the Pax4/6, Six1/2, Six3/6, Eya and Dac gene families [4,5]. Pax genes have been implicated in eye development in wide wide range mollusks, annelids, echinoderms, andand planarians [8,9,10,11].
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