Animals, especially those that migrate, need to locate and orient themselves in order to travel long distances in a reproducible manner. While their bodies experience many variable factors, such as wind, temperature, or other changing weather patterns, the Earth’s magnetic field is comparatively stable, providing animals with a reliable and global sensory field for geolocation and navigation. A variety of animals, from birds and bees to sea turtles and sharks, have been shown to utilize this magnetic field for navigational purposes, and many more animals, plants, and even single-cellular organisms are known to sense and respond to magnetic fields. Yet, the exact identities of the biological components that enable magnetoreception, or the ability to perceive magnetic fields, in living beings remain an open question.

A family of light-sensitive proteins called cryptochromes has garnered considerable attention from the scientific community as a candidate for such magnetic sensitivity. Cryptochrome proteins are located in the retinas of animals that display magnetosensitive behaviors, such as fish, amphibians, and birds. Furthermore, the prevalence of cryptochrome CRY4 was found to stay at a low level in chickens, which do not migrate, but it was observed to increase around the migratory season for robins. This indicates its potential role in migratory behavior. In a new study published in Nature, Xu and colleagues purified CRY4 found in the European robin’s eye and utilized spectroscopic techniques as well as computer simulations to characterize its magnetic properties. The researchers found that the protein possessed light-sensitive magnetic properties, allowing it to act as a magneto-sensor that can detect the Earth’s magnetic field. Importantly, such magnetic sensitivity was lower for the version of CRY4 found in chickens and pigeons.

While the results are certainly promising, in order to definitively prove that CRY4 is, indeed, the magnetosensitive substance that acts as the internal compass of migratory birds, the protein’s properties and function needs to be shown inside the bird’s eye. There, the scientists believe, the protein could possess even higher magnetosensitivity, and may work in concert with other substances that amplify its signal.

The lead author of the paper, Jingjing Xu is a doctoral student in the University of Oldenburg, Germany, working with Prof. Henrik Mouritsen, one of the corresponding authors of the paper. The collaboration consisted of 36 researchers from Germany, China, the United Kingdom, and the United States.

Corresponding author: Melis Tekant

Original article

 Image: Wikimedia Commons 

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