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Researchers discover specific protein and location in bird retina responsible for magnetic compass

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February 7, 2018 University of Southern Denmark

Migratory birds use a magnetic compass in their eye for navigation. Its basic sensory mechanisms have long remained elusive, but now researchers reveal exactly where in the eye, the birds’ control center for navigation is situated.

…In 2000 researchers suggested that a protein in the birds’ eye helps them take information from light and process it to a travel course: an inner magnetic compass. Since then the basic sensory mechanisms underlying this magnetoreception has remained elusive….

The magnetic compass sense in migratory birds is light dependent, and we wanted to find out which protein is at play. Theories have been circling around the so-called cryptochromes — but these cryptic proteins come in very different variations — so which one?

…To date, four different cryptochromes have been found in the retina of several bird species. Three of them show no relevance for magnetoreception, the researchers conclude.

But the fourth, Cry4, seems to be significantly different from its family members,” Ilia Solov’yov said.

When light hits cryptochromes in the eye of a migrating bird, they undergo chemical reactions that are influenced by the direction of Earth’s magnetic field, providing a signal of the bird’s orientation.

…They discovered that the Cry4 expression level in European robin retinae is significantly higher during the migratory season compared to the non-migratory seasons. “This is a strong indicator that the responsible protein is indeed cryptochrome 4.”…

…Inner compasses are not only found in migratory birds, but also in other animals such as bees.

“Understanding these inner compasses in animals can give us a fundamental knowledge of nature and maybe we can use it to protect wildlife. Many birds are killed in windmills, because they get disturbed by the turbulence around the mills. If we knew what magnetic fields exist around the mills, we maybe could construct some kind of protection zone around the mills,” said Ilia Solov’yov….

Anja Günther, Angelika Einwich, Emil Sjulstok, Regina Feederle, Petra Bolte, Karl-Wilhelm Koch, Ilia A. Solov’yov, Henrik Mouritsen. Double-Cone Localization and Seasonal Expression Pattern Suggest a Role in Magnetoreception for European Robin Cryptochrome 4. Current Biology, 2018; 28 (2): 211 DOI: 10.1016/j.cub.2017.12.003

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