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

11/9/2011 Nature  First published in 1869  Nature: Letters Vol 454: 21 August 2008 Cryptochrome mediates light-  Impact Factor: 36.101 dependent magnetosensitivity in Drosophila Presented by Natasha Pettifor and Michael Ocana The Authors The Authors  Robert J. Gegear, PhD  Amy Casselman  Assistant Professor  Ph. D student at the University of  Worcester Polytechnic Massachusetts Medical School Institute  Biology and Biotechnology  Postdoc at U. of Mass. Medical School in 2009 under Doctor Reppert  Brain plasticity, multimodal sensory integration The Authors The Authors  Scott Waddell, PhD  Steven M. Reppert, M.D.  Associate Professor  U Mass School of Medicine  U Mass School of Medicine  Neurobiology: Dept Chair  Neurobiology  Grad School of Biomedical  Grad School of Biomedical Sciences Sciences  Interdisciplinary  Interdisciplinary  Neuroscience  Neuroscience  Behavioral control, memory and motivation  Molecular Neuroethology 1

11/9/2011 Magnetic Fields & the Overview 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 Magnetoreception: What is magnetoreception? 3 forms?  Electromagnetic induction by the Earth ’ s magnetic  The ability of an animal to detect (geo)magnetic fields field  Generally accepted to be used by a number of both vertebrate and invertebrate species  Magnetite-based process  Chemical-based reactions …? Cryptochrome: photoreceptor… What is Cryptochrome? (Cry) and magnetorecptor?  Blue-light sensitive flavoprotein  How can one protein do both things?  Involved in circadian rhythms  Possibility : free-radicals, spin states & rxn products  Thought Trp-mediated  Cryptochrome or Cry has two forms …but probably not  Cry1 – Drosophila -like Cry  Cry2 – Vertebrate-like Cry  Proposed alternative:  Both present in some insects (e.g. the monarch) flavin transfers an electron to an unknown substrate. Only Cry1 present in Drosophila  The radical pairs are then Focus of the current paper  generated from this. Only Cry2 present in vertebrates  2

11/9/2011 Cryptochrome mediates light-dependent Cryptochrome mediates light-dependent magnetosensitivity in Drosophila magnetosensitivity in Drosophila  Purpose: study the potential chemical basis of  Experimental setup: magnetoreception, especially the role of Cryptochrome  Upper – Training  Lower – Testing  Drosophila only posses a single type of this protein, Cry 14 , which has a narrow activation range, peaking at  “ Preference index 350-400 nm and plateuing at 430-450 nm value ” calculated  Based on proportion of flies on magnetic field side of T-port Does Cry functionality depend on Naïve flies: strain comparison specific wavelengths of light?  Yes.  Canton-S strains had most profound response to field  Exhibited naïve avoidance  Black bars: trained flies  White bars: naïve flies How do we know it ’ s wavelength Is Cry required for this response? and not irradiance?  What is irradiance?  In cry 0 flies, the cry sequence was replaced completely  (Black is  Cry 01, cry 02 and cry 03 were cry 0 backcrossed onto w 1118 trained, white is  In cry b flies, a point mutation results in missense naïve)  w 1118 flies used as controls – all had same background  Irradiance levels:  w 1118 flies had a naïve lower in blue light preference for the  Low-intensity light: magnetic field effect of training remains  Wavelength-dependent 3

11/9/2011 Mutated Cry: naïve responses Mutated Cry: trained responses  Flies homozygous for  Controls trained to like the Cry 0 mutation failed the field even more to show naïve response  Cry 01 mutants can ’ t be  Heterozygotes favored trained the magnetic field Heterozygous Homozygous Trained and naïve responses of Cry and the circadian rhythm hetero- and homozygotes  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 Conclusions Cry and the circadian rhythm  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… 4