Light sensing starts with phototransduction in photoreceptor cells. The phototransduction cascade has diverged in different species, such as those mediated by transducin in vertebrate rods and cones, by Gq-type G protein in insect and molluscan rhabdomeric-type visual cells and vertebrate photosensitive retinal ganglion cells, and by Go-type G protein in scallop ciliary-type visual cells. Here, we investigated the phototransduction cascade of a prebilaterian box jellyfish, the most basal animal having eyes containing lens and ciliary-type visual cells similar to vertebrate eyes, to examine the similarity at the molecular level and to obtain an implication of the origin of the vertebrate phototransduction cascade. We showed that the opsin-based pigment functions as a green-sensitive visual pigment and triggers the Gs-type G protein-mediated phototransduction cascade in the ciliary-type visual cells of the box jellyfish lens eyes. We also demonstrated the light-dependent cAMP increase in the jellyfish visual cells and HEK293S cells expressing the jellyfish opsin. The first identified prebilaterian cascade was distinct from known phototransduction cascades but exhibited significant partial similarity with those in vertebrate and molluscan ciliary-type visual cells, because all involved cyclic nucleotide signaling. These similarities imply a monophyletic origin of ciliary phototransduction cascades distributed from prebilaterian to vertebrate.M any animals sense light signals for vision and nonvisual photoreceptions. Light is captured by an opsin-based photopigment in a photoreceptor cell and leads to cellular light response through a G protein-mediated phototransduction cascade. Three kinds of phototransduction cascades have been found thus far (1). In vertebrate rods and cones, the light is absorbed by visual pigment, and the information is relayed via transducin (G t ) (2), causing the decrease of intracellular cGMP concentration to close cyclic nucleotide-gated channels (3, 4). In rhabdomeric-type visual cells of higher invertebrates, such as arthropods and molluscans, G q -type G protein passes the light information to the phosphoinositol signaling cascade (5-9), which is also found in vertebrate photosensitive retinal ganglion cells (10). In addition, we reported that the G o -type G proteinmediated phototransduction cascade (11) involving in the cGMP increase as a second messenger exists in scallop ciliary visual cells (12). Recently, the G o -mediated phototransduction cascade was also found in the ciliary photoreceptor cells of lizard parietal eyes (13). These varied phototransduction cascades are, respectively, driven by particular opsins, which belong to phylogenetically distinct opsin subfamilies (1). Because vision has evolved with phototransduction cascades and has diverged in different species, the opsin-based pigment and signaling cascade of lower invertebrates, such as prebilaterian animals, is important to understand the evolution of phototransduction, especially the origin of vertebrate vision.The...

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SUMMARY1. By applying atomized chemical solutions on to gecko and carp retinae, neuropharmacological reactions of the photoreceptors and horizontal cells were observed.2. Sodium L-glutamate and L-aspartate, glycine, ACh and GABA, had no appreciable effect on the photoreceptor activity.3. Carp horizontal cells were depolarized by both L-glutamate and Laspartate. When maximally depolarized, the action of the endogenous transmitter from the receptor terminals was completely masked, resulting in abolition of the S-potentials.4. Responses to red light in both L-and C-type horizontal cells were more strongly affected by aspartate than responses to blue light.5. Glycine and GABA hyperpolarized the horizontal cells, and the Spotentials were diminished. 6. ACh had no effect on the activity of the horizontal cells.

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