title: Avian ultraviolet/violet cones identified as probable magnetoreceptors.
abstract: BACKGROUND
  The Radical-Pair-Model postulates that the reception of magnetic compass directions in birds is based on spin-chemical reactions in specialized photopigments in the eye, with cryptochromes discussed as candidate molecules. But so far, the exact subcellular characterization of these molecules in the retina remained unknown.
  
  
  RESULTS
  We here describe the localization of cryptochrome 1a (Cry1a) in the retina of European robins, Erithacus rubecula, and domestic chickens, Gallus gallus, two species that have been shown to use the magnetic field for compass orientation. In both species, Cry1a is present exclusively in the ultraviolet/violet (UV/V) cones that are distributed across the entire retina. Electron microscopy shows Cry1a in ordered bands along the membrane discs of the outer segment, and cell fractionation reveals Cry1a in the membrane fraction, suggesting the possibility that Cry1a is anchored along membranes.
  
  
  CONCLUSIONS
  We provide first structural evidence that Cry1a occurs within a sensory structure arranged in a way that fulfils essential requirements of the Radical-Pair-Model. Our findings, identifying the UV/V-cones as probable magnetoreceptors, support the assumption that Cry1a is indeed the receptor molecule mediating information on magnetic directions, and thus provide the Radical-Pair-Model with a profound histological background.
authors.affiliation: Fachbereich Biowissenschaften der J.W. Goethe-Universität Frankfurt, Frankfurt am Main, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Niessner
authors.forename: Susanne
authors.initials: S
authors.lastname: Denzau
authors.forename: Julia Christina
authors.initials: JC
authors.lastname: Gross
authors.forename: Leo
authors.initials: L
authors.lastname: Peichl
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Bischof
authors.forename: Gerta
authors.initials: G
authors.lastname: Fleissner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wiltschko
authors.forename: Roswitha
authors.initials: R
authors.lastname: Wiltschko
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology / Q000528:radiation effects; D002645:Chickens / Q000378:metabolism / Q000502:physiology*; D055358:Cone Opsins / Q000378:metabolism; D056931:Cryptochromes / Q000378:metabolism; D008280:Magnetics; D046109:Passeriformes / Q000378:metabolism / Q000502:physiology*; D021381:Protein Transport / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D055358:Cone Opsins; D056931:Cryptochromes