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Cryptochrome mediates light-dependent magnetosensitivity
in Drosophila Presented by Natasha Pettifor and Michael Ocana
Nature
First published in 1869
Nature: Letters Vol 454: 21 August 2008
Impact Factor: 36.101
The Authors
Robert J. Gegear, PhD Assistant Professor
Worcester Polytechnic Institute Biology and Biotechnology
Postdoc at U. of Mass. Medical School in 2009 under Doctor Reppert
Brain plasticity, multimodal sensory integration
The Authors
Amy Casselman
Ph. D student at the University of Massachusetts Medical School
The Authors
Scott Waddell, PhD Associate Professor
U Mass School of Medicine Neurobiology
Grad School of Biomedical Sciences Interdisciplinary
Neuroscience
Behavioral control, memory and motivation
The Authors
Steven M. Reppert, M.D.
U Mass School of Medicine
Neurobiology: Dept Chair
Grad School of Biomedical Sciences
Interdisciplinary
Neuroscience
Molecular Neuroethology
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Overview
Briefly: magnetic fields and magnetosensitivity
What is Cry? Why is it special?
Current paper – proof of Cry as a magnetoreceptor?
Magnetic Fields & the Geomagnetic Field.
Geomagnetic fields: caused by Earth’s molten interior. Weak: ~0.5 Gauss
Moving electric fields: vectors with direction and magnitude
What is magnetoreception?
The ability of an animal to detect (geo)magnetic fields
Generally accepted to be used by a number of both vertebrate and invertebrate species
…?
Magnetoreception: 3 forms?
Electromagnetic induction by the Earth’s magnetic field
Magnetite-based process
Chemical-based reactions
What is Cryptochrome? (Cry)
Blue-light sensitive flavoprotein
Involved in circadian rhythms
Cryptochrome or Cry has two forms
Cry1 – Drosophila-like Cry
Cry2 – Vertebrate-like Cry
Both present in some insects (e.g. the monarch)
Only Cry1 present in Drosophila
Focus of the current paper
Only Cry2 present in vertebrates
Cryptochrome: photoreceptor… and magnetorecptor?
How can one protein do both things?
Possibility: free-radicals, spin states & rxn products
Thought Trp-mediated …but probably not
Proposed alternative: flavin transfers an electron to an unknown substrate. The radical pairs are then generated from this.
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Cryptochrome mediates light-dependent magnetosensitivity in Drosophila
Purpose: study the potential chemical basis of magnetoreception, especially the role of Cryptochrome
Drosophila only posses a single type of this protein, Cry14, which has a narrow activation range, peaking at 350-400 nm and plateuing at 430-450 nm
Cryptochrome mediates light-dependent magnetosensitivity in Drosophila
Experimental setup:
Upper – Training
Lower – Testing
“Preference index value” calculated
Based on proportion of flies on magnetic field side of T-port
Naïve flies: strain comparison
Canton-S strains had most profound response to field
Exhibited naïve
avoidance
Does Cry functionality depend on specific wavelengths of light?
Yes.
Black bars: trained flies
White bars: naïve flies
How do we know it’s wavelength and not irradiance?
What is irradiance?
Irradiance levels: lower in blue light Low-intensity light:
effect of training remains
(Black is trained, white is naïve)
Is Cry required for this response?
In cry0 flies, the cry sequence was replaced completely
Cry01, cry02 and cry03 were cry0 backcrossed onto w1118
In cryb flies, a point mutation results in missense
w1118 flies used as controls – all had same background
w1118 flies had a naïve preference for the magnetic field
Wavelength-dependent
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Mutated Cry: naïve responses
Flies homozygous for the Cry0 mutation failed to show naïve response
Heterozygotes favored the magnetic field
Homozygous
Heterozygous
Mutated Cry: trained responses
Controls trained to like the field even more
Cry01 mutants can’t be trained
Trained and naïve responses of hetero- and homozygotes
Homozygous
Heterozygous Heterozygous
Transheterozygous
Cry and the circadian rhythm
The day-night cycle is regulated by the regular activation and inactivation of certain proteins over the day
Light acts as a major trigger to this cycle
Besides from its photosensitive functions, Cry also serves as a transcriptional regulator for some of these proteins
Cry and the circadian rhythm Conclusions
Drosophila can respond to a local magnetic field
Naïve reaction varies by strain
This response requires at least one copy of Cry
Disruption of circadian rhythm does not disrupt magnetic sensing ability
Solid behavioral assay for chemical- based magnetosensitivity (?... Do you agree?)
Many questions remain…
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