The ability to perceive geomagnetic fields (GMFs) represents a fascinating biological phenomenon. Studies on transgenic flies have provided evidence that photosensitive Cryptochromes (Cry) are involved in the response to magnetic fields (MFs). However, none of the studies tackled the problem of whether the Cry-dependent magnetosensitivity is coupled to the sole MF presence or to the direction of MF vector. In this study, we used gene silencing and a directional MF to show that mammalian-like Cry2 is necessary for a genuine directional response to periodic rotations of the GMF vector in two insect species. Longer wavelengths of light required higher photon fluxes for a detectable behavioral response, and a sharp detection border was present in the cyan/green spectral region. Both observations are consistent with involvement of the FADox, FAD(•-) and FADH(-) redox forms of flavin. The response was lost upon covering the eyes, demonstrating that the signal is perceived in the eye region. Immunohistochemical staining detected Cry2 in the hemispherical layer of laminal glia cells underneath the retina. Together, these findings identified the eye-localized Cry2 as an indispensable component and a likely photoreceptor of the directional GMF response. Our study is thus a clear step forward in deciphering the in vivo effects of GMF and supports the interaction of underlying mechanism with the visual system.

Department of Animal Physiology and Immunology Faculty of Science Masaryk University 611 37 Brno Czech Republic;

Department of Entomology National Taiwan University Taipei 106 Taiwan;

Department of Plant Physiology and Photobiology Faculty of Biology Philipps University D 35032 Marburg Germany

Department of Zoology and Animal Physiology Institute for Biology 2 RWTH Aachen University D 52056 Aachen Germany;

Institute of Entomology Biology Centre of Academy of Sciences of the Czech Republic 370 05 Ceske Budejovice Czech Republic;

Institute of Entomology Biology Centre of Academy of Sciences of the Czech Republic 370 05 Ceske Budejovice Czech Republic; Department of Molecular Biology Faculty of Science University of South Bohemia 370 05 Ceske Budejovice Czech Republic;

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