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The origin of vision: a palaeoinformatic approach. Davide Pisani The National University of Ireland, Maynooth. Vision and its fossil record Vision: the ability to detect an image, no matter how crude it is (e.g. the octopus, insects, crustaceans, spiders, and vertebrates).
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The origin of vision: a palaeoinformatic approach Davide Pisani The National University of Ireland, Maynooth
Vision and its fossil recordVision: the ability to detect an image, no matter how crude it is (e.g. the octopus, insects, crustaceans, spiders, and vertebrates). c. Lower-Cambrian ~530 Ma The fossil record is mute about the origin and early evolution of vision Animal genomes might be used in the absence of fossil evidence
Opsins: 7TM retinal binding proteins of approximately 40kDa. They loosely link a chromophore (retinal), through a Shiff’s base. Light sensitivity of the visual pigment is determined by the interaction of the chromophore and the opsin and is tuned to a particular wavelength of maximal absorption (max). When a Photon of appropriate wave-length hits an opsin it causes the chromophore to change its conformation. In turn, this changes the opsin three-dimensional structure and causes the release of neighboring G-protein alpha subunits, activating a signaling cascade. Paralogous Genes Two different Opsins YES Time & mutations Two Identical Opsins Duplication NO Ancestral Opsin Opsins + chromophore = visual pigments • Opsins are found in Vertebrates • Opsins are found in Bilaterians • Arthropoda, Annelida, Mollusca, Flatworms. • Opsins in “Lower Animals” • E.g. Cnidaria (corals jellyfishes) • Opsins in the animal outgroup • Choanoflagellate The animal chromophores use opsins. But different animals use different opsins in their chromophores We First used a BLAST-based approach to delimit opsin distribution in animals and their close relatives.
The earliest history of opsins (Blumlein & Pisani in prep)
Some conclusions & future directions • Opsins are an animal-specific gene family. • Duplications in the arthropods and vertebrates visual opsins seem coeval and seem to have significantly postdated the origin of opsins. Are these events correlated? • Was the origin of vision driven by the onset of complex predator-prey interactions? • Further insight will be obtained as more genomes will become available (particularly molluscs). Acknowledgments: Ms Alice Blumlein, Dr. J.O. McInerney.
