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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…