We at Webvision have a fascination with the evolution of the eye and are always looking for interesting papers that help describe from where, how and when vision came. This paper, Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye by Pavel Vopalenskya, Jiri Pergnera, Michaela Liegertova, Elia Benito-Gutierrez, Detlev Arendt, and Zbynek Kozmika attempts to answer the question of where the vertebrate eye came from. While the amphioxus has for many years been recognized as a viable candidate for the earliest vertebrate eye, the retinal structure is different from that of other vertebrates. Specifically, the photoreceptors of amphioxus are simple ciliated cells as opposed to the more sophisticated elaborations of structures on top of cillia in other vertebrate retinas. This paper describes in molecular terms, gene coexpression and structural features the different cell types of amphioxus in an attempt to define neuronal circuitry. Its a very cool paper that provides additional detail into the evolutionary origins of vision and we encourage you to have a look.
Image Credit: Hans Hillewaert from Wikipedia
Phototransduction is the process by which photon capture by opsins in photoreceptors is transduced into a neural signal. However, there are limits on visual sensitivity that are imposed by thermal means as opposed to the photochemical mechanisms resulting in activation of the phototransduction cascade.
The mechanism of this limit has long been a matter of debate, however this paper by Samer Gozem, Igor Schapiro, Nicolas Ferré and Massimo Olivucci demonstrates a mechanism. Mechanistically, the authors examined the maximum absorption wavelength (λmax) and the thermal activation kinetic constant (k) of different visual pigments which indicates that the thermal and photochemical activations are related. The authors found that rod opsin or rhodopsin possesses a transition state for thermal activation that has the same electronic structure as it does for photo-excitation. This results in spontaneous and random signals being generated in the rod photoreceptors that impose limits on visual sensitivity. Continue reading “Notable Paper: The Molecular Mechanism of Thermal Noise in Rod Photoreceptors”
This paper by Yumiko Umino, Nicolas Cuenca, Drew Everhart, Laura Fernandez-Sanchez, Robert B. Barlow and Eduardo Solessio examined late onset retinal degeneration in a model of diabetic retinopathy. Specifically, this manuscript attempted to examine the impact on retinas from the Gcgr knockout mice with long term high dietary glucose to see if that rescues retinal structure and physiology in the aged animal. Interestingly, prolonged exposure to to the diet induced euglycemia did improve retinal function, but did not result in re-restablishement of synaptic connectivity lost in hypoglycemia. The curious part about this is that there seems to be an ability to maintain metabolic status in these animals over long periods of time in spite of the loss of the synaptic connectivity.
Portraits made this year at the ISER meeting are up over on Jonesblog including a special treat from ISER president, Steve Fliesler at the bottom of the page. Enjoy…