Abstract
The eyes of vertebrates are invariant from cyclostome to human in many aspects, including the structure of the organ, morphology of the photoreceptors and the signal transduction in the photoreceptor cell. How vertebrate eyes have been established in the evolutional process is still enigma. Ascidians are the closest living relatives of the vertebrates. The tadpole larvae share a basic body plan with vertebrates, including notochord and dorsal tubular central nervous system. Therefore, this animal is expected to provide clue to evolution of vertebrate eyes. The authors have isolated the genes expressing in photoreceptor cells of ascidian larvae and prepared antibodies against these gene products. Using the antibodies, the authors have revealed the structure of the photoreceptors. In this review, the authors discuss the relationship between ascidian photoreceptors and vertebrate eyes on the basis of the photoresponse of the ascidian larva as well as the morphology.
