Photosensitivity and Magnetosensitivity of The Drosophila Circadian Clock

Abstract

The experiments in this thesis addressed whether magnetic fields can enhance entrainment (phase determination) of the circadian clock by light. The experiments were conducted using a species of small fruit flies, Drosophila melanogaster. A solenoid was built in order to create the magnetic field.A magnetic field was produced inside a wire coil by passing an electric current through the coil, with the strength of the field proportional to the current. Light pulses were produced by a monochromator in the incubator, while the programmable timer within the constant temperature incubator was used to produce12 hr.: 12 hr. light:dark (LD) cycles or constant illumination with blue light (LL).The effects of these treatments on Drosophila locomotor activity rhythms were measured in activity monitors. For the first part of the study, magnetic field pulses of 4.5mT (160-fold increase of the earth’s magnetic field) delivered together with blue light pulses at ZT15 produced an enhanced phase delay in subsequent circadian locomotor behavior in constant darkness, compared with the effect of light alone or magnetic fields alone. The effect was saturable and was observed within blue wavelength range (450nm±0.003nm) but not at red wavelengths (700nm±0.013nm). The second part of the study showed that 12hr:12hr cycles of magnetic field strength (oscillating between earth’s magnetic field and 160 times earth’s magnetic field) could drive 24hr cycles of locomotor activity in LL but had no effect on circadian phase of locomotor activity in constant darkness. The effect in constant light did not require the normal CRY photoreceptor protein because it was still observed in cryᵇ mutant flies, which remained rhythmic in LL and magnetism with the phase of the magnetic field rather than that of the previous LD cycle. The results demonstrate that a strong magnetic field can entrain the circadian clock in a light-dependent but CRY-independent manner.