Multimodal imaging reveals no evidence for magnetite-based magnetoreceptors in the mole-rat eye.

Magnetoreception is widespread across animals, but its sensory mechanism remains unresolved. One leading hypothesis proposes that single-domain magnetite is coupled to mechanosensitive ion channels. In subterranean Ansell's mole-rats, such receptors have been proposed to reside in the cornea or retina. We screened for magnetite in the mole-rat eye by combining iron imaging via enhanced Prussian blue staining and synchrotron X-ray fluorescence microscopy (XFM) with magnetic imaging via MRI-quantitative susceptibility mapping (MRI-QSM) and quantum-diamond microscopy. The retina and cornea contained little iron, most of which co-localized with titanium or chromium, indicating a non-biogenic origin. Iron-enriched lines in the cornea did not show ferrimagnetic signals. MRI-QSM revealed the highest susceptibility in the ciliary body, where iron-rich pigmented cells were identified. A targeted TEM-screen, however, failed to detect single-domain magnetite particles. In conclusion, we found no evidence of magnetite-based magnetoreceptors in the cornea or retina, suggesting other tissues or mechanisms underlie mole-rat magnetoreception.