Nature First published in 1869 Nature: Letters Vol 454: 21 August - - PDF document

11/9/2011 1 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

• f 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…