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Leading Edge 246 Cell 139, October 16, 2009 2009 Elsevier Inc.
 

Summary: Leading Edge
Review
246 Cell 139, October 16, 2009 2009 Elsevier Inc.
Introduction
The great majority of animals have photoreceptors of one sort or
another for detecting food source, mate, predator/prey, orienta-
tion, or simply the light/dark cycle dictated by the movement of
the sun. Such photoreceptors, whether ocular or extraocular, are
generally distinguishable into two types: ciliary and rhabdomeric,
depending on whether the proliferation of photosensitive mem-
branes necessary for efficient light absorption is derived from a
modified cilium or from microvillar projections of the apical cell
surface forming a rhabdom (for review, Arendt, 2003; Lamb et al.,
2007). Uniformly, these photoreceptors sense light with a visual
pigment composed of a vitamin A-based chromophore and a
seven-transmembrane-helix apoprotein, opsin. These pigments
are prototypical G protein-coupled receptors (GPCRs), signaling
via heterotrimeric G proteins. More than 1000 opsins have now
been identified in the animal kingdom, all believed to originate
from a common ancestor and separate from the structurally simi-

  

Source: Alford, Simon - Department of Biological Sciences, University of Illinois at Chicago

 

Collections: Biology and Medicine