Transcript Pisani
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). 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 + chromophore = visual pigments Paralogous Genes Two different Opsins Time & mutations YES 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 the chromophore and the opsin use and opsins. is tuned toBut a particular animal chromophores wavelength of maximal absorption (max). When a Photon of different animals use different opsins in their appropriate wave-length hits an opsin it causes the chromophore to chromophores change its conformation. In turn, this changes the opsin threedimensional structure and causes the release of neighboring Gprotein alpha subunits, activating a signaling cascade. We First used a BLAST-based approach to delimit opsin distribution in animals and their close relatives. Two Identical Opsins • • Duplication NO • • Ancestral Opsin 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 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.