Molecular basis of magnetoreception in fish

• Applicant: Professorin Dr. Gabriele Gerlach
• Subject Area: Sensory and Behavioural Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530759521

In the ocean, millions of fish are migrating to find habitats for breeding, feeding, and settlement in often distant areas. Migrating in the ocean is dangerous because complex currents, and the associated risk of drift, make orientation difficult. Nevertheless, even after a long migration, fish often reach their destination, for example, their birthplace. In addition to olfactory, acoustic and visual signals, fish also use magnetic field perception, which we humans do not have. While magnetic reception itself is undisputed, and great progress has been made in recent years in studying it in birds, for example, the mechanisms by which fish can perceive changes in the magnetic field are not yet understood. In birds, the protein cryptochrome 4 in retinal visual receptors is thought to be critical for magnetic field perception. In bony fish, two main mechanisms are discussed: perception of the magnetic field via iron crystals (magnetites) and cryptochrome-based magnetoreception. Here, we would like to investigate whether and what role cryptochrome proteins play in fish magnetoreception. For magnetic field perception corresponding to birds, the cryptochrome protein would need to have a flavin adenine dinucleotide (FAD) binding motif and 3 - 4 tryptophans. Our preliminary studies show that some migratory fish species, such as the marine three-spined stickleback (Gasterosteus aculeatus) or salmon (Oncorhynchus spec.), in which magnetic field perception has been demonstrated, do not possess Cry4 but a structure-like Cry5. The non-migratory zebrafish possesses both. To determine whether one or even both cryptochromes are involved in magnetic field perception, we plan to perform gene knockouts of cry4 and cry5 in zebrafish based on the CRISPR/Cas9 method. To test their effects, we designed a conditioning experiment in which wild-type zebrafish significantly alter their behavior and position in response to a single change in magnetic field. By testing the knockout fish, we could determine if the response to magnetic field changes is lost in the mutants. Migrating sticklebacks can also be conditioned with the developed behavioral test. This provides the critical prerequisite to analyze possible differences in magnetic field perception between non-migratory zebrafish and migratory sticklebacks. We aim to analyze the functionality of the Cry4 and Cry5 proteins as potential magnetic field sensors by heterologously expressing the binding affinity of FAD. In their fit, these experiments provide a great opportunity to further elucidate the mechanism of magnetic field perception in fish and thus understand the phenomenon of how fish find their way.

• DFG Programme: Research Grants