Bio-GPS: A Way to Get Around
(November 21st, 2017) Magnetoreception is a fascinating sense but scientists still don't understand how it functions. Currently, three ideas are being tested, amongst others by researchers in Vienna.
For some birds, the prospect of travelling thousands for kilometres just to look for the tastiest food or the perfect breeding grounds is perfectly normal. Take the Artic Tern, for example. This small bird weighing no more than 150 g manages to enjoy a permanent summer as it migrates from pole to pole in a yearly 70,900 km round trip.
For a long time, this ability was a complete mystery. In the mid-1800s, Russian zoologist Alexander von Middendorf suggested that birds were able to travel by sensing the Earth’s magnetic field but it took more than 100 years for the idea to stick. In the 1960s, it was finally shown that birds do have an in-built magnetic GPS, and since then, the list has expanded to include bacteria, turtles and lobsters, to name just a few.
Nowadays, the idea of a magnetic sense may be generally accepted but the exact mechanism remains just as baffling as it was for von Middendorf. One of the groups trying to unveil this mystery is based at the Research Institute of Molecular Pathology in Vienna, where David Keays and his team use the latest techniques to tackle this issue.
As Keays explains in a recent review published in PLOS Biology, there are currently three big ideas being tested. The first one relies on a magnetite-based receptor. In theory, this protein – probably linked to a ferromagnetic structure such as magnetite – undergoes conformational changes in response to the magnetic field. For example, this is exactly what happens in magnetotactic bacteria, where this internal compass guides these organisms to waters with more favourable redox conditions.
However, the search for a similar mechanism in higher organisms has been frustrating. “For a long time, my group and other groups have been looking for cells that contain magnetite, but it’s fair to say that it’s not been a very successful endeavour. Primarily, people have looked at cells that contain iron, but this has been problematic because there are so many cells in the body that contain iron”, says Keays.
The second theory is based on a light-sensitive chemical-based compass. “This involves a radical pair mechanism and is really embedded in quantum physics”, continues Keays. The magnetic field may be able to influence biochemical reactions by altering the spin state of a pair of radical electrons. (If you’re curious about this subject, last year Lab Times dedicated an entire feature article looking at quantum biology).
Finally, the third idea was initially proposed in the late-1800s but has largely been overlooked. This idea requires some yet to be found structure, able to convert the magnetic field into an electrical stimulus. Reflecting Faraday’s Law of Electromagnetic Induction, the idea is that changes in the magnetic field could induce oscillations in the cells’ electric potential, which in turn could activate a metabolic response. “People think it works in the case of animals that move in conductive medium, like sharks, for example”, says Keays.
After years working in this field, Keays admits it’s harder to solve the mystery than he had imagined. “I don’t think I’m magnetically-sensitive, which makes designing experiments more challenging, because I don’t have any intuitive sense of what it feels like to detect a magnetic field”, says the researcher. This also makes detecting any interferences virtually impossible and researchers have to go to great lengths to control every imaginable variable. To add to the difficulty, the primary sensory cells could literally be anywhere in the animal, from head to toe. “It’s not like trying to find a needle in a haystack”, jokes Keays, “it’s like trying find a needle in a haystack of needles. That’s why it is so difficult”.
Despite the setbacks, the IMP team are still keen to decipher the enigma of magnetic function with the help of modern tools available in neuroscience, including imaging techniques and genetic studies. “We’re applying all these emerging technologies to the problem to solve the mystery”, concludes Keays.
Photo: Public Domain/Zureks