Interview Magnetic attraction

A number of different including , and many insects, birds and fish are able to instinctively detect magnetic fields. Humans are not thought to have this ability, although this has been questioned by some. Many species, most notably migratory birds and fish, make use of this capability to navigate long distances. The exact physiological mechanism that

organisms use to magnetic fields has been much debated among experts. To find out more about this fascinating area of Downloaded from http://portlandpress.com/biochemist/article-pdf/40/2/38/851749/bio040020038.pdf by guest on 26 September 2021 research, Helen Albert spoke to Professor Michael Winklhofer from the University of Oldenburg in Germany, a biophysicist with a special interest in magnetoreception and its molecular mechanisms.

to escape predators. Yet, it is not known how they navigate all the way to the Sargasso Sea where they spawn and eventually die. We think they have memorized the juvenile migration route from the hatching site in the form of a cognitive map, based on Michael Winklhofer trained in physics with special chemical (salinity, odorants) and physical parameters focus on of fine particles. He started (water temperature, currents, ). working in the field of biomagnetism as the focus Sensing these parameters on the return journey and for his PhD at Munich University, during which he comparing them with the setpoints from the internal examined theoretically how magnetic particles could map could keep the fish on track. The magnetic field is be used as a physical substrate for the magnetic sense particularly useful because it defines a stable reference in . He moved on to study magnetotactic frame as opposed to other parameters. bacteria, which biomineralize particles in their cell body to align it with magnetic fields. His From a molecular point of view, how do they research has included devising magnetic protocols to sense geomagnetic fields? detect biogenic magnetite in sediments and tissues. That is still the million dollar question – so far, we He became a Professor in the Faculty of Mathematics do not have an unequivocal structural candidate for a and Natural Sciences at the University of Oldenburg magnetoreceptor cell, which we could study and work in 2016. He now uses behavioural, neuroanatomical out the physical and molecular mechanism of magnetic and molecular approaches to pursue his favourite field transduction. There are two main contenders for research question, namely, how do migratory the molecular substrate of magnetic-field reception, animals sense the Earth’s magnetic field and use it magnetite particles and . The magnetite for orientation? pathway is conceptually simple, because the magnetic field exerts a mechanical torque or force on these, which Your 2012 PNAS paper focused on could be detected by mechanosensory ion channels in characterizing magnetite-based specialized sensory cells. The cryptochrome hypothesis, magnetoreceptor cells in trout. How do on the other hand, assumes that the magnetic field is fish know when to migrate and what route sensed by its effect on a (light-dependent) radical-pair to follow? reaction hosted in the cryptochrome, Fish migration is a broad field, with the details so that the magnetic field would be converted into a depending on the particular group of fish, their biochemical response. preferred habitats, and lifestyle. Regardless, migration Sharks, rays, and some other fish equipped to a spawning site requires good timing to make sure with fine electroreceptive organs may sense the the fish arrive there when mating partners are present. magnetic field by way of electromagnetic induction. The European and American eel, for example, appears But that mechanism is not feasible for birds, to rely on external factors such as water temperature , mammals, or fish such as salmon that lack and daylight hours to know the rough time window electroreceptors. Other substrates for magnetic for migration out into the ocean. The actual journey sensing have been suggested, but have failed to begins at high water level on a dark night, probably demonstrate physical feasibility.

38 April 2018 © Biochemical Society Interview Downloaded from http://portlandpress.com/biochemist/article-pdf/40/2/38/851749/bio040020038.pdf by guest on 26 September 2021

Do other creatures sense magnetic fields? If so, do they use the same molecular mechanisms? While the mentioned earlier are the best example of using magnetite for orientation, it would go too far to refer to this passive alignment as magnetic sensing. In insects, magnetite (in honeybees) and cryptochrome (in Drosophila) have been implicated in mediating some magnetic- field dependent behavioural responses, but the jury is still out on this.

Is ‘magnetoreception’ only used for the purposes of migration or does this ability have other uses? Further reading There are several examples in the kingdom of so-called magnetic alignment, for example, Australian • Hore P. J. and Mouritsen H. The Radical-Pair Mechanism mounds are found to be oriented along the of Magnetoreception. Annual Review of Biophysics magnetic North-South axis. Similarly, some mammals 2016 45: 1, 299-344 https://doi.org/10.1146/annurev- were reported to align their body axis with the magnetic biophys-032116-094545 axis when at rest. However, we still do not know the whys • Cadiou H., McNaughton P.A. Avian magnetite-based and wherefores of this alignment and whether it is truly magnetoreception: a physiologist’s perspective. J. R. Soc. magnetoreception-based behaviour. Interface 2010 7 S193-S205 https://doi.org/10.1098/ rsif.2009.0423.focus Research piblished in Scientific Reports last year • Eder SH, Cadiou H, Muhamad A, McNaughton PA, suggests that it may be possible to ‘train’ the Kirschvink JL, Winklhofer M. Magnetic characterization of human to sense the geomagnetic North. isolated candidate magnetoreceptor cells. Proc Can the ability to sense magnetic fields be Natl Acad Sci U S A. 2012; 109(30): 12022-7. https://doi. induced or switched off experimentally? org/10.1073/pnas.1205653109 That is an exciting study indeed, demonstrating • Schumann F, O’Regan JK. Sensory augmentation: that the human brain can also integrate an artificial integration of an auditory compass signal into human magnetic reference (here delivered acoustically) in its of space. Sci Rep. 2017; 7: 42197. https://doi. multimodal perception of head orientation in space. org/10.1038/srep42197 Head orientation is normally perceived relative to • Hand E. Maverick scientist thinks he has discovered a the optical flow, hence the magneto-acoustic tool magnetic sixth sense in humans. Science. Jun. 23, 2016. could serve as spatial orientation aid when vision is https://doi.org/10.1126/science.aaf5803 impaired. Of course, the most tantalizing question is • Myklatun A, Lauri A, Eder SHK et al. Zebrafish and medaka whether humans have the ability to sense the magnetic offer insights into the neurobehavioral correlates of field without a technical sensor. According to Joe vertebrate magnetoreception. Nat. Commun. 2018; 9: 802. Kirschvink, a pioneer in magnetoreception research, https://10.1038/s41467-018-03090-6 the answer is yes! ■

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