Magnetoreception: activated cryptochrome 1a concurs with magnetic orientation in birds

Abstract

The radical pair model proposes that the avian magnetic compass is based on radical pair processes in the eye, with cryptochrome, a flavoprotein, suggested as receptor molecule. Cryptochrome 1a (Cry1a) is localized at the discs of the outer segments of the UV/violet cones of European robins and chickens. Here, we show the activation characteristics of a bird cryptochrome in vivo under natural conditions. We exposed chickens for 30 min to different light regimes and analysed the amount of Cry1a labelled with an antiserum against an epitope at the C-terminus of this protein. The staining after exposure to sunlight and to darkness indicated that the antiserum labels only an illuminated, activated form of Cry1a. Exposure to narrow-bandwidth lights of various wavelengths revealed activated Cry1a at UV, blue and turquoise light. With green and yellow, the amount of activated Cry1a was reduced, and with red, as in the dark, no activated Cry1a was labelled. Activated Cry1a is thus found at all those wavelengths at which birds can orient using their magnetic inclination compass, supporting the role of Cry1a as receptor molecule. The observation that activated Cry1a and well-oriented behaviour occur at 565 nm green light, a wavelength not absorbed by the fully oxidized form of cryptochrome, suggests that a state other than the previously suggested Trp•/FAD• radical pair formed during photoreduction is crucial for detecting magnetic directions.

Blue-light dependent ROS formation by Arabidopsis cryptochrome-2 may contribute toward its signaling role

“…Such effects have been observed for cryptochromes in other systems as well. 7 Secondly, a new localization for cry2 can also be clearly observed inside the nucleus of permeabilized cells (Fig. 1, panel k, l).…”

Zebra finches have a light-dependent magnetic compass similar to migratory birds

“…Cryptochromes are the only known vertebrate photopigments to form long-lived, spin-correlated radical pairs upon light excitation (Ritz et al, 2000). They have been reported in several animal groups, including insects (Emery et al, 1998;Gegear et al, 2010), amphibians (Eun et al, 2003), birds (Mouritsen et al, 2004;Möller et al, 2004;Wiltschko et al, 2007a;Liedvogel and Mouritsen, 2010;Nießner et al, 2013;Fusani et al, 2014;Du et al, 2014) and mammals (van der Horst et al, 1999;Avivi et al, 2004). The light-absorbing cofactor of cryptochromes, flavin adenine dinucleotide (FAD), exists in three redox states with different absorption spectra ( Fig.…”

“…•− (Solov'yov and Schulten, 2009;Müller and Ahmad, 2011;Nießner et al, 2013Nießner et al, , 2014Wiltschko et al, 2016; reviewed by Wang et al, 2015).…”

No evidence for intracellular magnetite in putative vertebrate magnetoreceptors identified by magnetic screening

“…The first, known as the radical pair hypothesis, argues that the spin state of a light-induced radical pair is influenced by the Earth's magnetic field, which, in turn, affects the biochemical properties of a signaling protein (8). This protein is hypothesized to be the blue-light sensitive molecule cryptochrome (9)(10)(11). The second concept, known as the magnetite hypothesis, argues that the magnetic iron oxide magnetite (Fe 3 O 4 ) is coupled to a mechanosensitive ion channel.…”