126
Electromagnetic Fields in Biological Systems
Yoshii, Ahmad, and Helfrich-Förster (2009) demonstrated that Drosophila’s circadian
clock is sensitive to magnetic fields and that this sensitivity depends on the light activation of CRY and the applied field strength, consistent with the radical pair mechanism.
The CRY is widespread throughout biological systems and has been suggested as the
receptor for magnetic compass orientation in migratory birds. The results establish the
circadian clock of Drosophila as a model system for CRY-dependent magnetic sensitivity. Furthermore, given that CRY occurs in multiple tissues of Drosophila, including
those potentially implicated in flying orientation, future studies may yield insights that
could be applicable to the magnetic compass of migratory birds and even to potential
magnetic field effects in humans. As another CRY-related mechanism, Zaporozhan
and Ponomarenko (2010) hypothesized that CRY is a transcriptional repressor of the
major circadian complex CLOCK/BMAL1 (reviewed by Langmesser et al. 2008) and,
therefore, magnetic fields via some modulation of CRY function can influence circadian
gene expression and modify the activity of the transcription factor nuclear factor-κB
(NF-κB)- and glucocorticoids-dependent signaling pathways.
The radical pair mechanism imposes some constraints that should be satisfied by a
viable chemical magnetoreceptor (Rodgers and Hore 2009). For this purpose, computer
simulations have been performed on a collection of radical pairs undergoing restricted
rigid body rotation, coherent anisotropic spin evolution, electron spin relaxation, and
spin-selective recombination reactions. Lau et al. (2010) showed that perfect molecular ordering and complete immobilization, as in a crystal at low temperatures, are not
requirements for efficient radical pair magnetoreception. It is acceptable to have radical pairs that are uniaxially ordered with a moderate order parameter, which undergo
medium-amplitude orientational fluctuations with respect to the director and whose
motional correlation time is longer than about a quarter of their lifetime. The authors
assumed that a magnetosensitive CRY specifically bound to a visual receptor protein,
rhodopsin, would share its orientational ordering and motional restriction and hence
could have the properties necessary for efficient magnetoreception. Hill and Ritz (2010)
modeled the effect of molecular disorder on the performance of a radical pair compass
and estimated the minimum number of radical pairs required in a receptor cell to achieve
a certain resolution in terms of directional and intensity variations of a magnetic field.
More recently, Phillips, Jorge, and Muheim (2010) suggested that the effects of
light on magnetic compass orientation are mediated by a light-dependent magnetoreception mechanism or instead are due to input from a non-light-dependent (e.g.,
magnetite-based) magnetoreception mechanism that secondarily interacts with other
light-dependent processes.
Regarding magnetite-based magnetoreception, an experimental study in European
robins, E. rubecula, suggested that the interactions between the magnetite receptors in
the beak and the visual system occurring at higher levels in the brain do not involve the
magnetoreception system based on radical pair process in the right eye, but rather they
involve other, nonlateralized components of the visual system (Wiltschko et al. 2010).
Winklhofer and Kirschvink (2010) proposed a magnetite hypothesis and focused on
“magnetic torque transducer models,” where elongated magnetic structures like a chain
of magnetosomes respond to a magnetic field by restricted rotational motion about
an elastic pivot. These authors theoretically analyzed interactions of magnetosomes
Electromagnetic Fields in Biological Systems
Yoshii, Ahmad, and Helfrich-Förster (2009) demonstrated that Drosophila’s circadian
clock is sensitive to magnetic fields and that this sensitivity depends on the light activation of CRY and the applied field strength, consistent with the radical pair mechanism.
The CRY is widespread throughout biological systems and has been suggested as the
receptor for magnetic compass orientation in migratory birds. The results establish the
circadian clock of Drosophila as a model system for CRY-dependent magnetic sensitivity. Furthermore, given that CRY occurs in multiple tissues of Drosophila, including
those potentially implicated in flying orientation, future studies may yield insights that
could be applicable to the magnetic compass of migratory birds and even to potential
magnetic field effects in humans. As another CRY-related mechanism, Zaporozhan
and Ponomarenko (2010) hypothesized that CRY is a transcriptional repressor of the
major circadian complex CLOCK/BMAL1 (reviewed by Langmesser et al. 2008) and,
therefore, magnetic fields via some modulation of CRY function can influence circadian
gene expression and modify the activity of the transcription factor nuclear factor-κB
(NF-κB)- and glucocorticoids-dependent signaling pathways.
The radical pair mechanism imposes some constraints that should be satisfied by a
viable chemical magnetoreceptor (Rodgers and Hore 2009). For this purpose, computer
simulations have been performed on a collection of radical pairs undergoing restricted
rigid body rotation, coherent anisotropic spin evolution, electron spin relaxation, and
spin-selective recombination reactions. Lau et al. (2010) showed that perfect molecular ordering and complete immobilization, as in a crystal at low temperatures, are not
requirements for efficient radical pair magnetoreception. It is acceptable to have radical pairs that are uniaxially ordered with a moderate order parameter, which undergo
medium-amplitude orientational fluctuations with respect to the director and whose
motional correlation time is longer than about a quarter of their lifetime. The authors
assumed that a magnetosensitive CRY specifically bound to a visual receptor protein,
rhodopsin, would share its orientational ordering and motional restriction and hence
could have the properties necessary for efficient magnetoreception. Hill and Ritz (2010)
modeled the effect of molecular disorder on the performance of a radical pair compass
and estimated the minimum number of radical pairs required in a receptor cell to achieve
a certain resolution in terms of directional and intensity variations of a magnetic field.
More recently, Phillips, Jorge, and Muheim (2010) suggested that the effects of
light on magnetic compass orientation are mediated by a light-dependent magnetoreception mechanism or instead are due to input from a non-light-dependent (e.g.,
magnetite-based) magnetoreception mechanism that secondarily interacts with other
light-dependent processes.
Regarding magnetite-based magnetoreception, an experimental study in European
robins, E. rubecula, suggested that the interactions between the magnetite receptors in
the beak and the visual system occurring at higher levels in the brain do not involve the
magnetoreception system based on radical pair process in the right eye, but rather they
involve other, nonlateralized components of the visual system (Wiltschko et al. 2010).
Winklhofer and Kirschvink (2010) proposed a magnetite hypothesis and focused on
“magnetic torque transducer models,” where elongated magnetic structures like a chain
of magnetosomes respond to a magnetic field by restricted rotational motion about
an elastic pivot. These authors theoretically analyzed interactions of magnetosomes