Abstract
Migratory birds can sense the Earth’s magnetic field and use it for orientation over thousands of kilometres. A light-dependent radical-pair mechanism associated with the visual system is currently discussed as the underlying mechanism of the magnetic compass sense. The blue light receptor cryptochrome 4 (Cry4) is considered as the most likely primary sensory protein that detects the geomagnetic field. Since the protein interaction partners of Cry4 are completely unknown at present, here, we aim to identify potential candidate interaction partners of Cry4 in the avian retina. We used the yeast-two-hybrid system to screen avian cDNA libraries for possible interaction partners of Cry4 in the European robin. The UAS-GAL yeast two hybrid system was applied to confirm a group of candidate Cry4 interaction partners. Six proteins were found to be particularly promising candidates for interacting with European robin Cry4. The identified genes code for guanine nucleotide-binding protein G(t) subunit alpha-2 (GNAT2), long-wavelength-sensitive opsin (LWS, also called iodopsin), guanine nucleotide-binding protein subunit gamma 10 (GNG10), potassium voltage-gated channel subfamily V member 2 (KCNV2), retinol binding protein 1 (RBP1) and retinal G protein-coupled receptor (RGR). All genes are known to be expressed in vertebrate retinae of different species. We conclude by discussing putative signalling pathways that could connect cryptochrome 4 to one or more of these 6 candidates.
Highlights
Migratory birds can sense the Earth’s magnetic field and use it for orientation over thousands of kilometres
Behavioural studies have provided widely accepted experimental evidence that many night-migratory songbirds employ a magnetic compass as well as a magnetic map for orientation[2,3,4]. These behavioural studies further showed that birds sense the inclination of the geomagnetic field and not its polarity[1,5,6]; that magnetoreception in migratory birds depends on blue light[7,8], and that magnetic compass information is detected in both eyes[9,10] and processed in specific parts of the birdsvisual system[11,12,13]
We tested for any background signals due to auto-activation by comparing the immunoblot results of empty Y2H vectors with ErCry[4] containing vectors (Fig. 1A)
Summary
Migratory birds can sense the Earth’s magnetic field and use it for orientation over thousands of kilometres. Günther et al.[26] demonstrated that Cry[4] is expressed in the outer segments of the double cone and long-wavelength single cone photoreceptor cells in the retinae of migratory European robins, which could be an ideal location for a primary magnetoreceptor molecule[18]. The signalling state in a Cry molecule from a night-migratory songbird is presently unknown, the current working hypothesis suggests that photoexcitation of the FAD co-factor in Cry followed by electron transfer from three or four neighbouring tryptophan residues leads to the formation of a magnetically sensitive radical pair Qin et al.[30] have reported the results of a computational screening approach based on an alternative hypothesis They predicted that an avian magnetoreceptor could be an iron-sulphur protein, and they claimed that the ubiquitously present protein IscA1 (dubbed MagR) is a direct interaction partner of Cry[4]. These concerns will be addressed in more detail in the discussion part
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