Localisation of the Putative Magnetoreceptive Protein Cryptochrome 1b in the Retinae of Migratory Birds and Homing Pigeons.

Petra Bolte,Ulrike Janssen‐Bienhold,Henrik Mouritsen,Miriam Liedvogel,Florian Bleibaum,Angelika Einwich,Dominik Heyers,Anne Depping,Lars Wöhlbrand,Ralf Rabus,Anja Günther,Eric James Warrant

doi:10.1371/journal.pone.0147819

Petra Bolte, Ulrike Janssen‐Bienhold + Show 10 more

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https://doi.org/10.1371/journal.pone.0147819

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Abstract

Cryptochromes are ubiquitously expressed in various animal tissues including the retina. Some cryptochromes are involved in regulating circadian activity. Cryptochrome proteins have also been suggested to mediate the primary mechanism in light-dependent magnetic compass orientation in birds. Cryptochrome 1b (Cry1b) exhibits a unique carboxy terminus exclusively found in birds so far, which might be indicative for a specialised function. Cryptochrome 1a (Cry1a) is so far the only cryptochrome protein that has been localised to specific cell types within the retina of migratory birds. Here we show that Cry1b, an alternative splice variant of Cry1a, is also expressed in the retina of migratory birds, but it is primarily located in other cell types than Cry1a. This could suggest different functions for the two splice products. Using diagnostic bird-specific antibodies (that allow for a precise discrimination between both proteins), we show that Cry1b protein is found in the retinae of migratory European robins (Erithacus rubecula), migratory Northern Wheatears (Oenanthe oenanthe) and pigeons (Columba livia). In all three species, retinal Cry1b is localised in cell types which have been discussed as potentially well suited locations for magnetoreception: Cry1b is observed in the cytosol of ganglion cells, displaced ganglion cells, and in photoreceptor inner segments. The cytosolic rather than nucleic location of Cry1b in the retina reported here speaks against a circadian clock regulatory function of Cry1b and it allows for the possible involvement of Cry1b in a radical-pair-based magnetoreception mechanism.

Highlights

Migratory birds use the Earth's magnetic field for orientation and navigation on their migratory journeys [1,2,3]
A more detailed analysis of garden warbler Cry1b (gwCry1b) immunoreactivity in the ganglion cell layer together with a nuclear marker indicated that the amount of Cryptochrome 1b (Cry1b) protein differed between individual GCs (Fig 1G and 1H)
Both the diffuse background labelling found in all retinal layers and the lack of specific labelling of individual cell populations in control stainings, where we used the pre-immune serum instead of the primary gwCry1b antibody, allowed us to exclude the possibility that the observed Cry1b labelling was due to unspecific reactions with antibodies present before immunisation of the animals (Fig 1C and 1D, shown in green)

Summary

Introduction

Migratory birds use the Earth's magnetic field for orientation and navigation on their migratory journeys [1,2,3]. If we assume that the state of the transient radical alters the relative photosensitivity of the receptor molecule, radical-pair-mediated magnetoreception would allow the detection of the symmetry plane or axial orientation of the field lines, but not their polarity This is in line with the fact that night-migratory songbirds use an “inclination compass”, which is sensitive to the axis of the Earth’s magnetic field lines, but not to their polarity [1,2]

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