Animal Magnetism

A photosensitive protein behind the retinas of cockroaches plays a role in light-dependent, directional magnetosensitivity.

By Catherine Offord | May 1, 2016

CRY IN THE EYE: The cryptochrome Cry2, involved in magnetosensing, is present in the eyes of two cockroach species, including Blattella germanica (above). © ISTOCK.COM/ERIKKARITS


The Paper
O. Bazalova et al., “Cryptochrome 2 mediates directional magnetoreception in cockroaches,” PNAS, doi:10.1073/pnas.1518622113, 2016.

Protein with a Purpose
Many animals make use of light-dependent sensitivity to magnetic fields (MFs) to navigate their environment. Researchers recently implicated cryptochrome 1 (Cry1)—a photosensitive protein involved in circadian clock function in Drosophila—in fruit fly magnetoreception. This led David Dolezel of the Institute of Entomology at the Czech Academy of Sciences and colleagues to ask whether Cry2, a vertebrate-type cryptochrome also present in many insects, mediates sensitivity to the presence and directionality of MFs in other animals.

Restless Roaches
Previously, the investigators found that two cockroach species with Cry2 become more restless when subjected to rotating (rather than steady) MFs. Using magnetically induced restlessness (MIR) as a measure of sensitivity to MF directionality, the team set out to test the importance of Cry2 in detecting rotation.

No Cry
Dolezel’s group found that either silencing Cry2 or covering cockroaches’ eyes with opaque paint abolished MIR when the insects were presented with rotating MFs, establishing both the protein and the eye as necessary for directional magnetoreception. “Vertebrate-type cryptochrome, which is not thought by most to have a lot of light sensitivity, actually may,” says Steven Reppert of the University of Massachusetts Medical School, who was not involved in the work. “This study in the cockroach adds a lot of credibility to that prospect.”

Challenges Ahead
Although the researchers located Cry2 behind the retina, “we don’t know if we’re hitting the magnetosensor or something downstream,” says Dolezel, adding that “cryptochrome is like chewing gum—it interacts with everything.”

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