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

Yoshii T, Ahmad M, Helfrich-Förster C - PLoS Biol. (2009)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: University of Regensburg, Institute of Zoology, Regensburg, Germany.

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.

Show MeSH

Related in: MedlinePlus

Period Changes (+ SEM) 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 μT) and Blue LightIn cryb mutants CRY cannot bind its chromophore flavin, cryOUT mutants 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 (F3,76 = 29.88; p < 0.001). A consecutive post-hoc test revealed that cryb and cryOUT mutants 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.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2667543&req=5

pbio-1000086-g004: Period Changes (+ SEM) 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 μT) and Blue LightIn cryb mutants CRY cannot bind its chromophore flavin, cryOUT mutants 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 (F3,76 = 29.88; p < 0.001). A consecutive post-hoc test revealed that cryb and cryOUT mutants 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.

Mentions: So far our results are consistent with the idea that magnetoreception involves a radical-pair mechanism occurring in a photopigment. In the next step we wanted to know whether CRY might be the relevant photopigment, so we tested cryb mutants in which FAD binding is impaired [38] and cryOUT mutants that lack CRY completely [25]. As expected, both mutants show short periods under blue light of 0.18 μW/cm2 (Figure 2C), because TIM is not degraded due to the mutation in the CRY protein (e.g., [34]). The free-running periods of cryb and cryOUT mutants were 23.4 ± 0.05 h (n = 25) and 23.7 ± 0.04 h (n = 26), respectively. After exposure to the 300 μT magnetic field, 88.0% of cryb flies and 76.9% of cryOUT flies 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.


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

Yoshii T, Ahmad M, Helfrich-Förster C - PLoS Biol. (2009)

Period Changes (+ SEM) 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 μT) and Blue LightIn cryb mutants CRY cannot bind its chromophore flavin, cryOUT mutants 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 (F3,76 = 29.88; p < 0.001). A consecutive post-hoc test revealed that cryb and cryOUT mutants 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.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2667543&req=5

pbio-1000086-g004: Period Changes (+ SEM) 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 μT) and Blue LightIn cryb mutants CRY cannot bind its chromophore flavin, cryOUT mutants 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 (F3,76 = 29.88; p < 0.001). A consecutive post-hoc test revealed that cryb and cryOUT mutants 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.
Mentions: So far our results are consistent with the idea that magnetoreception involves a radical-pair mechanism occurring in a photopigment. In the next step we wanted to know whether CRY might be the relevant photopigment, so we tested cryb mutants in which FAD binding is impaired [38] and cryOUT mutants that lack CRY completely [25]. As expected, both mutants show short periods under blue light of 0.18 μW/cm2 (Figure 2C), because TIM is not degraded due to the mutation in the CRY protein (e.g., [34]). The free-running periods of cryb and cryOUT mutants were 23.4 ± 0.05 h (n = 25) and 23.7 ± 0.04 h (n = 26), respectively. After exposure to the 300 μT magnetic field, 88.0% of cryb flies and 76.9% of cryOUT flies 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.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: University of Regensburg, Institute of Zoology, Regensburg, Germany.

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.

Show MeSH
Related in: MedlinePlus