Download Cryptochrome mediates light-dependent

11/9/2011
Nature
 First published in 1869
 Nature: Letters Vol 454: 21 August 2008
Cryptochrome mediates lightdependent magnetosensitivity
in Drosophila
 Impact Factor: 36.101
Presented by Natasha Pettifor and Michael Ocana
The Authors
 Robert J. Gegear, PhD
 Assistant Professor
 Worcester Polytechnic
Institute
The Authors
 Amy Casselman
 Ph. D student at the University of
Massachusetts Medical School
 Biology and Biotechnology
 Postdoc at U. of Mass.
Medical School in 2009 under
Doctor Reppert
 Brain plasticity, multimodal sensory integration
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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11/9/2011
Overview
Magnetic Fields & the
Geomagnetic Field.
 Briefly: magnetic fields and magnetosensitivity
 What is Cry? Why is it special?
 Current paper – proof of Cry as a magnetoreceptor?
 Moving electric fields:
vectors with direction and
magnitude
 Geomagnetic fields: caused by Earth’s
molten interior. Weak: ~0.5 Gauss
What is magnetoreception?
 The ability of an animal to detect (geo)magnetic
fields
Magnetoreception:
3 forms?
 Electromagnetic induction by the Earth’s magnetic
field
 Generally accepted to be used by a number of both
vertebrate and invertebrate species
 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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11/9/2011
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
Does Cry functionality depend on
specific wavelengths of light?
 Yes.
 Exhibited naïve
avoidance
 Black bars:
trained flies
 White bars:
naïve flies
How do we know it’s wavelength
and not irradiance?
 What is irradiance?
Is Cry required for this response?
 In cry0 flies, the cry sequence was replaced completely
 (Black is
trained,
white is
naïve)
 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
 Irradiance levels:
lower in blue light
 Low-intensity light:
effect of training remains
 w1118 flies had a naïve
preference for the
magnetic field
 Wavelength-dependent
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11/9/2011
Mutated Cry: naïve responses
Mutated Cry: trained responses
 Flies homozygous for
the Cry0 mutation failed
to show naïve response
 Controls trained to like
the field even more
 Cry01 mutants can’t be
trained
 Heterozygotes favored
the magnetic field
Heterozygous
Homozygous
Trained and naïve responses of
hetero- and homozygotes
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
Homozygous
Transheterozygous
Heterozygous
Heterozygous
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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