Cryptochrome mediates light-dependent magnetosensitivity of Drosophila's circadian clock.

Abstract

Since 1960, magnetic fields have been discussed as Zeitgebers for circadian clocks, but the mechanism by which clocks perceive and process magnetic information has remained unknown. Recently, the radical-pair model involving light-activated photoreceptors as magnetic field sensors has gained considerable support, and the blue-light photoreceptor cryptochrome (CRY) has been proposed as a suitable molecule to mediate such magnetosensitivity. Since CRY is expressed in the circadian clock neurons and acts as a critical photoreceptor of Drosophila's clock, we aimed to test the role of CRY in magnetosensitivity of the circadian clock. In response to light, CRY causes slowing of the clock, ultimately leading to arrhythmic behavior. We expected that in the presence of applied magnetic fields, the impact of CRY on clock rhythmicity should be altered. Furthermore, according to the radical-pair hypothesis this response should be dependent on wavelength and on the field strength applied. We tested the effect of applied static magnetic fields on the circadian clock and found that flies exposed to these fields indeed showed enhanced slowing of clock rhythms. This effect was maximal at 300 muT, and reduced at both higher and lower field strengths. Clock response to magnetic fields was present in blue light, but absent under red-light illumination, which does not activate CRY. Furthermore, cry(b) and cry(OUT) mutants did not show any response, and flies overexpressing CRY in the clock neurons exhibited an enhanced response to the field. We conclude that Drosophila's circadian clock is sensitive to magnetic fields and that this sensitivity depends on light activation of CRY and on the applied field strength, consistent with the radical pair mechanism. CRY is widespread throughout biological systems and has been suggested as receptor for magnetic compass orientation in migratory birds. The present data 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 fly 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.

Full text

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Cryptochrome Mediates Light-Dependent
Magnetosensitivity of Drosophila’s
Circadian Clock
Taishi Yoshii1, Margaret Ahmad2, Charlotte Helfrich-Fo ¨rster1*
1 University of Regensburg, Institute of Zoology, Regensburg, Germany, 2 Universite ´ Paris VI, PCMP, Paris, France
Since 1960, magnetic fields have been discussed as Zeitgebers for circadian clocks, but the mechanism by which clocks
perceive and process magnetic information has remained unknown. Recently, the radical-pair model involving light-
activated photoreceptors as magnetic field sensors has gained considerable support, and the blue-light photoreceptor
cryptochrome (CRY) has been proposed as a suitable molecule to mediate such magnetosensitivity. Since CRY is
expressed in the circadian clock neurons and acts as a critical photoreceptor of Drosophila’s clock, we aimed to test the
role of CRY in magnetosensitivity of the circadian clock. In response to light, CRY causes slowing of the clock,
ultimately leading to arrhythmic behavior. We expected that in the presence of applied magnetic fields, the impact of
CRY on clock rhythmicity should be altered. Furthermore, according to the radical-pair hypothesis this response should
be dependent on wavelength and on the field strength applied. We tested the effect of applied static magnetic fields
on the circadian clock and found that flies exposed to these fields indeed showed enhanced slowing of clock rhythms.
This effect was maximal at 300 lT, and reduced at both higher and lower field strengths. Clock response to magnetic
fields was present in blue light, but absent under red-light illumination, which does not activate CRY. Furthermore, cryb
and cryOUTmutants did not show any response, and flies overexpressing CRY in the clock neurons exhibited an
enhanced response to the field. We conclude that Drosophila’s circadian clock is sensitive to magnetic fields and that
this sensitivity depends on light activation of CRY and on the applied field strength, consistent with the radical pair
mechanism. CRY is widespread throughout biological systems and has been suggested as receptor for magnetic
compass orientation in migratory birds. The present data 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 fly 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.
Citation: Yoshii T, Ahmad M, Helfrich-Fo ¨rster C (2009) Cryptochrome mediates light-dependent magnetosensitivity of Drosophila’s circadian clock. PLoS Biol 7(4): e1000086.
doi:10.1371/journal.pbio.1000086
Introduction
Endogenous clocks help organisms to adapt to the 24-h
cycle of the earth. One of the main characteristics of
endogenous clocks is that they continue to oscillate even in
the absence of external time cues. Under such conditions,
they ‘‘free-run’’ with their endogenous inherited periods that
are slightly different from 24 h. Therefore, they are also called
circadian clocks. Under natural conditions circadian clocks
are synchronized to the 24-h cycle on Earth by different
Zeitgebers. The most important Zeitgeber is the light–dark
cycle, but temperature, humidity, and the social environment
can also serve as Zeitgebers. Additionally, magnetic fields
have been discussed as agents that synchronize circadian
clocks since 1960, when Brown et al. [1] found that the
circadian rhythms of fiddler crabs and other organisms are
influenced by small changes in the intensity of Earth’s
magnetic field. In particular, the electromagnetic field with
a frequency of 10 Hz is known to show a prominent 24-h
oscillation [2]; thus, the field could serve as geophysical
synchronizer of the circadian clock. Although electromag-
netic fields are not consciously perceived by humans, Wever
[3] demonstrated that the circadian activity rhythm of
humans can be entrained by an artificial 10 Hz electro-
magnetic field, mimicking the natural oscillations on Earth.
The activity of mice, house flies, and fruit flies could also be
synchronized or phase-shifted by 10 Hz electric fields applied
for 12 h daily [4,5]. Cyclically changing intensities of a static
magnetic field can also work as weak synchronizers of the
circadian clock, as shown by Bliss and Heppner [6] for house
sparrows. The latter study was motivated by the idea that
birds perform magnetic compass orientation and that this
ability depends on a functional clock. Thus, the authors
speculated about a link between the magnetosense and the
circadian clock.
Despite the compelling effects of (electro)-magnetic fields
on the circadian clock, the mechanisms by which the
magnetic field is perceived and how it manipulates circadian
Academic Editor: Ueli Schibler, University of Geneva, Switzerland
Received September 9, 2008; Accepted March 3, 2009; Published April 7, 2009
Copyright: ? 2009 Yoshii et al. This is an open-access article distributed under the
terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author
and source are credited.
Abbreviations: CRY, cryptochrome; DD, constant darkness; FAD, flavin adenine
dinucleotide; LED, light-emitting diode; LL, constant light; SEM, standard error of
the mean; TIM, Timeless; UV, ultraviolet
* To whom correspondence should be addressed. E-mail: charlotte.foerster@
biologie.uni-regensburg.de
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P PL Lo oS S BIOLOGY

Page 2

clocks are unknown. Two main models of magnetic field
sensing are currently under discussion: (1) the magnetite
model proposing a primary process involving tiny crystals of
permanently magnetic material [7], and (2) the radical-pair
model suggesting a ‘‘chemical compass’’ based on singlet–
triplet transitions in photopigments [8–10].
The radical-pair mechanism, in which the magnetosensor is
a photopigment, was first suggested by Schulten and cow-
orkers [8–10]. The first step of the reaction is the absorption
of a photon of light energy by the pigment molecule, leading
to the transient formation of radical pairs (unpaired
electrons) with opposite electron spin states (singlet elec-
trons). The model predicts that these electrons are close
enough together that the unpaired electron spin states can
undergo transition, at some frequency, from antiparallel to
parallel spin states (singlet–triplet intersystem crossing). Such
singlet–triplet intersystem crossing is a natural feature of
many photochemical reactions that, in fact, may have nothing
to do with magnetosensitivity and is the result of the system
reaching the most energetically favorable state subsequent to
absorption of photon energy. The critical feature of a
magnetosensitive radical-pair reaction is that the radicals
have a sufficiently long lifetime and are oriented in such a
way that singlet–triplet transitions are modified by their
alignment in the presence of an applied magnetic field. In
such a case, product yield or rate of formation would be
different depending on the relative amount of singlet or
triplet formation, and these changes in output would provide
a means for the organisms to detect the effects of even very
weak applied fields. This presumed radical-pair mechanism
has indeed been observed experimentally in reactions
involving organic compounds [11] and in biological systems
such as photosynthetic reaction centers [12,13].
Since the radical-pair mechanism of magnetosensitivity
depends on the activation of the relevant photopigment by
light, it is wavelength dependent. Magnetosensitivity is
maximal at the absorbance maximum of the photopigment,
and it depends on the strength of the magnetic field. Ritz et
al. [10] calculated the yield of the triplet products in relation
to the strength of the magnetic field and the angle of the field
with respect to the alignment of the radical pair in space.
They found that there is a small window of the magnetic field
strength at which the radical-pair mechanism furnishes
magnetosensory capacities. In agreement with these calcu-
lations, Wiltschko and Wiltschko found that the magnet
compass orientation of birds works only at a certain range of
magnetic intensities [14].
That magnetoperception is wavelength dependent has
been shown not only in birds but also in newts and fruit
flies. As photopigments, cryptochromes (CRYs) have been
proposed [9,15,16]. CRYs are UV- and blue-absorbing photo-
receptors, found in plants and animals, that contain flavin
adenine dinucleotide (FAD) as chromophore [17] and have
been shown to form radical pairs subsequent to light
activation [18]. CRYs are expressed in the eyes of mammals
[19] and migratory birds [20,21], where crucial magneto-
receptors have been localized [22,23]. However, CRYs are also
expressed in the circadian clock neurons of mice and flies
[24–27]. This raises the possibility that magnetic fields can
interact directly with the circadian clock.
The fruit fly Drosophila melanogaster is best suited to reveal a
putative role of CRYs in the magnetosensitivity of the
circadian clock, because there is only one CRY, and because
mutants are available that either knock out the binding
domain of the FAD (crybmutants, [28]) or the entire CRY
molecule (cry0mutants, [29]; cryOUTmutants, [25]; cryDmutants,
[30]). The molecular mechanisms of the circadian clock are
largely unraveled. The main players of the clock are the clock
genes period, timeless, Clock, and cycle, which participate in
complex molecular feedback loops to generate the circadian
oscillation [31,32]. CRY is known to play an important role in
the photoreception pathway to Drosophila’s endogenous clock
[27]. Light promotes the binding of CRY to TIMELESS (TIM),
leading to the degradation of TIM [33,34]. Under light–dark
cycles the action of CRY leads to a ‘‘reset’’ of the clock every
morning. However, under constant light (LL), TIM-mediated
degradation by CRY occurs continuously. Therefore, the
amount of TIM is reduced and the clock slows down (i.e., the
free-running period of the locomotor rhythm is lengthened).
When the constant illumination exceeds a critical intensity
(. 10 lx), TIM disappears completely and the clock stops
running (the flies become arrhythmic [35]).
On the basis of the background described above we
speculated that a magnetic field might influence the circadian
clock via CRY under blue light but not red light conditions.
To investigate this possibility, we measured the free-running
periods of the flies’ locomotor rhythms before and during
exposure to a magnetic field under constant weak blue light
or red light illumination. The blue and red lights were
adjusted to such low intensities that in the absence of the
magnetic field the flies showed only a slightly longer period
than when they were under constant dark (DD) conditions.
We found that 40% of the flies further lengthened the free-
running periods during the exposure to a magnetic field of
300 lT under blue light illumination. This effect was
completely absent under red light conditions. We also
demonstrate that the response of fruit flies to the magnetic
field is not only wavelength dependent, but also dependent
on the strength of the magnetic field, as is implied by the
radical-pair model. Furthermore, the magnetic field could
not induce any period lengthening in cryband cryOUTmutant
flies; but period lengthening was enhanced after overexpress-
PLoS Biology | www.plosbiology.org April 2009 | Volume 7 | Issue 4 | e10000860814
Magnetosensitivity of the Fly Clock
Author Summary
Magnetic fields influence endogenous clocks controlling the sleep–
wake cycle of animals, but the underyling mechanisms are unclear.
Birds that can do magnetic compass orientation also depend on
light, and the blue-light photopigment cryptochrome was proposed
to act as a navigational magnetosensor. Here we tested the role of
cryptochrome as a light-dependent magnetosensor of the clock in
the fruit fly Drosophila melanogaster. In wild-type flies we found that
constant magnetic fields slowed down the speed of the clock in a
dose-dependent manner—but only in the presence of blue light. In
mutants lacking functional cryptochrome, the magnetic fields had
no significant effects on the endogenous clock, whereas the effects
were enhanced after overexpression of cryptochrome. Our data
suggest that cryptochrome works as a magnetosensor in the
endogenous clock when it is excited by blue light. Our work
supports previous data showing that fruit flies need functional
cryptochrome to perceive a magnetic field, demonstrating that the
interaction of cryptochome and magnetic fields are not just for the
birds.

Page 3

ing CRY in the clock neurons. Our results indicate that the
magnetic field influences the circadian clock via CRY.
Results
Finding the Right Settings
The illumination of the flies was a critical parameter
during our experiments, because we intended to activate
CRY, but not to such an extent that arrhythmic behavior
would occur. We recorded the flies under different intensities
of blue light (465–470 nm) and found that 0.18 lW/cm2was a
suitable light intensity for the experiments, at which the flies
did not become arrhythmic, but showed a significant period
lengthening. The mean period at 0.18 lW/cm2blue light was
25.8 6 0.14 h (mean 6 standard error of the mean [SEM], n¼
25). This period was 1.7 h longer than under DD conditions
[36], indicating that CRY was activated by the constant weak
blue light and that it provoked a constant weak TIM
degradation. Our rationale was that we should see further
changes in the free-running period of the flies as soon as they
were exposed to the magnetic field affecting the singlet–
triplet intersystem crossing of FAD in light-activated CRY.
Effects of Magnetic Fields on the Free-Running Period
In a first experiment we tested the influence of magnetic
fields of different intensities (Figure 1). The radical-pair
mechanism predicts that there should be an optimal
magnetic strength and that the effects would be smaller
under too low or too high magnetic fields [9]. To enable
comparison with previous experiments [37] we chose static
magnetic fields of 0 lT, 150 lT, 300 lT, and 500 lT; excepting
the control of 0 lT these are, respectively, 3, 6, and 10 times
stronger than natural magnetic fields. The free-running
periods of the flies were determined before and during the
application of the constant magnetic fields and the changes in
period were calculated (independent of their direction). We
found that even flies without exposure to a magnetic field
exhibited period changes over the recording time, but that
these changes were significantly smaller than those occurring
under the influence of a magnetic field of 300 lT (Figures 2A,
2B and 3A). ANOVA revealed that the period changes
depended significantly on the strength of the magnetic field
(Figure 3A). Most flies lengthened their periods in response to
the magnetic field (Figure 2A); but there are also some flies
with shortened periods (Figure 2B). To quantify the number
of flies with shortened and lengthened periods we defined the
following categories (Table 1): Flies exhibiting period changes
smaller than 0.5 h (as most wild-type flies did) were defined as
flies showing no effects. Flies with shortened or lengthened
periods by 0.5 h or more were defined as flies showing period
shortening or lengthening, respectively. The third category
consisted of flies in which periodogram analysis could not
detect any significant period. These were defined as arrhyth-
mic. v2analysis revealed that the number of flies with
lengthened periods was significantly higher when a magnetic
field of 300 lT was applied (Table 1).
Next we tested whether the effect of the magnetic field
depends on the wavelength of the constant light. For that
purpose the experiments were performed under a constant
red light (625–630 nm) of 0.18 lW/cm2, with or without
applying a field of 300 lT. We found no difference in period
changes between the two groups (Figure 3B; Table 1). This
result clearly indicates that the lengthening of the periods by
the magnetic field is dependent on the wavelength.
Cryptochrome Is Involved in Magnetoreception
So far our results are consistent with the idea that
magnetoreception involves a radical-pair mechanism occur-
ring in a photopigment. In the next step we wanted to know
whether CRY might be the relevant photopigment, so we
tested crybmutants in which FAD binding is impaired [38]
and cryOUTmutants that lack CRY completely [25]. As
expected, both mutants show short periods under blue light
of 0.18 lW/cm2(Figure 2C), because TIM is not degraded due
to the mutation in the CRY protein (e.g., [34]). The
free-running periods of cryband cryOUTmutants were 23.4
6 0.05 h (n ¼ 25) and 23.7 6 0.04 h (n ¼ 26), respectively.
After exposure to the 300 lT magnetic field, 88.0% of cryb
flies and 76.9% of cryOUTflies did not show any period
changes (Figure 2C; Table 1), and when changes occurred
these were significantly smaller than those in wild-type flies
(Figure 4). This indicates that CRY is involved in the
magnetically sensitive response of the fly.
Next we wanted to test whether we could not only diminish
the responses to the magnetic field by knocking out CRY, but
also increase the responses by overexpressing CRY in the
clock neurons. This test could be done by expressing CRY
under the control of the strong clock-gene promoter of the
timeless gene (in timgal4/uas-cry flies). The circadian clock of
such flies shows increased light sensitivity [38], and accord-
ingly we found that CRY-overexpressing flies showed signifi-
cantly longer free-running periods than wild-type flies under
Figure 1. Schematic Representation of the Experimental Apparatus
The locomotor recording device was described in detail previously
[59,60]. Here eight of 32 spectrophotometer cuvettes are shown as
representative ‘‘houses’’ for flies. Two monochromatic LEDs were placed
in front of each cuvette, and the flies were illuminated homogenously in
the cuvettes. Helmholtz coils were placed above and below the
recording device, generating a static magnetic field (dotted light with
arrows) perpendicular to the plane of the recording device. The infrared
sensors for monitoring the activity of the flies were on the ends of the
cuvettes opposite the LED illumination.
doi:10.1371/journal.pbio.1000086.g001
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Magnetosensitivity of the Fly Clock

Page 4

blue light. This result indicates that the higher amount of
light-activated CRY degrades TIM to a greater extent. The
average period of the 24 tested CRY-overexpressing flies was
26.9 6 0.33 h, and one fly showed arrhythmicity. After
exposure to the magnetic field, most CRY-overexpressing flies
became arrhythmic (Figure 2D; Table 1) and the remaining
ones showed large period changes (Figure 4). All flies except
one lengthened their free-running periods (Table 1). These
results show that the degree of responsiveness to the
magnetic field is directly linked to the levels of CRY present
in the fly, and that the site of action of the magnetic field
effect can be directly localized to the clock neurons, in which
CRY is active in setting the circadian clock.
Discussion
We show here that Drosophila’s clock is magnetosensitive,
and that this sensitivity depends on CRY. When the first
studies were performed that showed magnetosensitivity of
the circadian clock, CRY had not been detected yet and the
mechanism of how the clock is influenced by magnetic fields
was completely elusive. Now, we know that CRY is expressed
in the clock neurons of Drosophila [25,30], that CRY absorbs
UV and blue-green light [39], and that CRY consecutively
binds to TIM and induces its degradation [34]. Under
constant conditions this process leads to period lengthening
or arrhythmicity [35]. The magnetic field effect that we
observed in our study led to further lengthening of the
period, in the same way as an increased intensity of blue light
would lead to enhanced CRY function. The effect of a
magnetic field was particularly pronounced in CRY-over-
expressing flies, in which small differences in CRY function
should be significantly amplified. Additionally, we could show
that this reaction depends on the strength of the magnetic
field and on the wavelength of the light. Red light that is
outside of the absorption and action spectra of CRY [39–42]
did not provoke significant responses. Consistent with the
involvement of cryptochrome, cryband cryOUTmutants
respond neither to blue-green light nor to the magnetic field.
Our results strongly support the radical-pair model
suggesting light-activated flavin-based photoreceptors as
sensors for magnetic fields. In several animals magneto-
reception has been shown to depend preferentially on blue
light [43–47]. Ritz et al. [10] stated first that CRYs are suitable
molecules for such photoreceptor-based magnetoreception.
CRYs are blue-green photoreceptors in plants and flies
[17,28,48,49] and have been shown to form radical pairs
upon photoexcitation [18] as is true for the closely related
Figure 2. Representative Free-Running Locomotor Rhythms before and during the Exposure to a Magnetic Field
Actograms of two wild-type flies (A and B), one crybmutant (C) and one CRY-overexpressing fly (tim-gal4;uas-cry) (D) are depicted. All flies were exposed
to blue light of 0.18 lW/cm2throughout the experiment and to a magnetic field of 300 lT during the second half of the experiment (indicated by gray
areas). The free-running periods of 40% of wild-type flies lengthened (A) and 12% shortened (B) during exposure to the magnetic field. These effects were
not observed in the majority of crybmutant flies (C). More than 60% of CRY-overexpressing flies exhibited arrhythmicity after the magnetic field (D).
doi:10.1371/journal.pbio.1000086.g002
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DNA photolyases [50]. Other classes of photoreceptors, such
as phototropins [51] and chlorophylls [52] found in plants,
also undergo radical-pair reactions. However, rhodopsins,
which are the major photosensory pigments in flies and other
animals, are not able to form radical pairs because photo-
excitation leads to cis–trans isomerization of retinal rather
than an electron transfer [53]. Thus, CRYs are the only
currently known class of molecules found in animals that are
likely to fulfill the physical and chemical characteristics that
are required for functioning as the primary magnetic sensor.
The first evidence that CRYs may work as magnetosensors
comes from the plant Arabidopsis thaliana, where it was shown
that CRYs mediate magnetic field-dependent hypocotyl
growth inhibition under blue light [37]. In these experiments,
the effect of the magnetic field was to increase the plant’s
response to perceived blue light by enhancing cryptochrome
activity, similarly to the presently observed magnetic field
effect in flies. The second evidence comes from the fly D.
melanogaster (that paper was published during the preparation
of the present manuscript [54]). Gegear et al. [54] showed
clearly that fruit flies need functional CRY to perceive a
magnetic field that was paired with a sugar reward during a
classical learning experiment. Although this study did not
analyze the effect of magnetic field strength on CRY activity,
these data are highly consistent with our present observations
that the magnetic field intensifies the effects of blue light on
the clock. The radical-pair mechanism predicts that the rate
or yield of product formation from such a reaction will be
altered by an applied magnetic field. Therefore, the pairing of
Figure 3. Period Changes (þSEM) Observed in the Free-Running Rhythm
of Wild-Type Flies after Application of Magnetic Fields under Blue Light
and Red Light Illumination
Under blue light (A), magnetic fields of different strength were applied,
and ANOVA revealed that the observed period alterations significantly
depended on the strength of the magnetic field (F3,101¼3.0; p¼0.03). A
post-hoc test revealed that the period change at 300 lT was significantly
different from that at 0 lT. Under red light (B), the period alterations
produced by a magnetic field of 300 lT were not significantly different
from those occurring spontaneously (without a magnetic field). Numbers
in the columns indicate the number of included flies. Flies that became
arrhythmic are excluded from this analysis (compare Table 1).
doi:10.1371/journal.pbio.1000086.g003
Table 1. Percentages of flies That Show Alterations in Rhythmic Behaviour after Application of a Magnetic Field
Strain/Light
Conditions
Magnetic
Field Conditionsn
Arrhythmic
Flies
Flies with
Period
Lengthening
Flies with
Period
Shortening
Flies
without
Effects
Red light, wild-typea
0 lT 24
23
29
26
25
27
26
25
26
24
0%
0%
8.3%
8.7%
3.4%
38.5%
40.0%
22.2%
50%
4.0%
11.5%
25.0%
16.7%
26.1%
17.2%
7.7%
12.0%
3.7%
3.8%
4.0%
3.8%
4.2%
75.0%
65.2%
72.4%
53.8%
40.0%
66.7%
46.2%
84.0%
77.0%
4.2%
300 lT
0 lT
150 lT
300 lT
500 lT
tim-gal4;þ
cryb
cryOUT
tim-gal4;uas-cry
Blue light, wild-typeb
6.0%
0%
8.0%
7.4%
0.0%
8.0%
7.7%
66.7%
Blue light, mutants, 300 lTc
aUnder red light, v2-analysis revealed no significant differences in the amount of flies showing period changes in presence and absence of the magnetic field (v2¼ 0.65; p ¼ 0.72).
bUnder blue light, v2-analysis revealed significant differences in the amount of flies showing period lengthening under the different magnetic fields (v2¼ 15.07; p ¼ 0.02).
cFlies with manipulated CRY behaved differently with high significance (v2¼ 41.48; p , 0.001).
doi:10.1371/journal.pbio.1000086.t001
Figure 4. Period Changes (þSEM) Observed in the Free-Running Rhythm
of Wild-Type and Control Flies and Fly Strains with Manipulated CRY after
Application of a Magnetic Field (300 lT) and Blue Light
In crybmutants CRY cannot bind its chromophore flavin, cryOUTmutants
are devoid of CRY, and tim-gal4;uas-cry flies have CRY overexpressed in
all clock neurons. ANOVA revealed a significant influence of the strain on
the period change (F3,76¼29.88; p , 0.001). A consecutive post-hoc test
revealed that cryband cryOUTmutants exhibited significantly less period
change than CRY-overexpressing flies, which showed significant larger
period changes than all other strains. Numbers in or above the columns
indicate the number of included flies. Since most tim-gal4;uas-cry flies
became arrhythmic in the magnetic field (Table 1) only eight flies could
be included in the analysis.
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Magnetosensitivity of the Fly Clock