An electromagnetic field disrupts negative geotaxis in Drosophila via a CRY-dependent pathway.

Giorgio Fedele,Edward W. Green,Ezio Rosato,Charalambos P. Kyriacou

doi:10.1038/ncomms5391

Abstract

Many higher animals have evolved the ability to use the Earth’s magnetic field, particularly for orientation. Drosophila melanogaster also respond to electromagnetic fields (EMFs), although the reported effects are quite modest. Here we report that negative geotaxis in flies, scored as climbing, is disrupted by a static EMF, and this is mediated by cryptochrome (CRY), the blue-light circadian photoreceptor. CRYs may sense EMFs via formation of radical pairs of electrons requiring photoactivation of flavin adenine dinucleotide (FAD) bound near a triad of Trp residues, but mutation of the terminal Trp in the triad maintains EMF responsiveness in climbing. In contrast, deletion of the CRY C terminus disrupts EMF responses, indicating that it plays an important signalling role. CRY expression in a subset of clock neurons, or the photoreceptors, or the antennae, is sufficient to mediate negative geotaxis and EMF sensitivity. Climbing therefore provides a robust and reliable phenotype for studying EMF responses in Drosophila.

Highlights

Many higher animals have evolved the ability to use the Earth’s magnetic field, for orientation
Magnetic induction, which can only be applied to marine creatures, owing to the high conductivity of salt water[1,2], the magnetite hypothesis that proposes a process mediated by crystals of permanently magnetic material[1] and the radical pair mechanism (RPM), which relies on a chemical reaction involving specialized photoreceptors[3,4]
We conclude that negative geotaxis requires both blue-light activation and the presence of CRY, and that climbing can be disrupted by a static electromagnetic fields (EMFs)

Summary

Introduction

Many higher animals have evolved the ability to use the Earth’s magnetic field, for orientation. In the RPM, the first step of the reaction requires absorption of a photon by the pigment molecule, leading to the transient formation of a radical pair of electrons in an overall singlet state (antiparallel spin orientation), in which the two unpaired electrons are at a suitable distance to undergo transition to the triplet state (parallel orientation) This transition may be sensitive to an electromagnetic field (EMF), altering the singlet-triplet balance. The two experimental paradigms that utilized cry mutations in flies include a conditioning[13,18] and a circadian behavioural assay[14] In these studies, CRYs have been implicated as mediators of the fly’s EMF responses in a wavelength-dependent manner. We conclude that negative geotaxis provides a reliable method for studying behavioural responses to EMFs

Methods

Results

Conclusion