Davide Pisani

The National University of Ireland, Maynooth

The origin of vision: a palaeoinformatic

approach

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 + chromophore = visual pigments

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.

Ancestral Opsin

Two Identical Opsins

Duplication

Time

&

mutations

Two different Opsins

Paralogous Genes

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.

YES

NO

• 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.