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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).
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.