These crystals are predicted to be similar in shape and size ( 4– 7) to iron mineral crystals biosynthesized by magnetotactic bacteria (MTB) for use in magnetotaxis, passive alignment to geomagnetic fields ( 8). A leading hypothesis posits that specialized sensory organelles containing crystals of magnetite physically interact with Earth‐strength magnetic fields to transduce geomagnetic information into neural signals ( 1, 4– 7). Consistent with deep homology, we present an evolutionary genetics hypothesis for magnetite formation among eukaryotes to motivate convergent approaches for examining magnetite-based magnetoreception, molecular origins of matrix-associated biomineralization processes, and eukaryogenesis.ĭiverse animals utilize the Earth’s magnetic field for orientation and navigation cues however, the receptor mechanism that underlies this sensory ability remains a fundamental question in sensory biology ( 1– 3). We also show that 11 prokaryote biomineralization genes are universally present among a diverse set of eukaryote taxa and that nine of those genes are present within the Asgard clade of archaea Lokiarchaeota that affiliates with eukaryotes in phylogenomic analysis. Here, we discover that salmonid olfactory epithelium contains magnetite crystals arranged in compact clusters and determine that genes differentially expressed in magnetic olfactory cells, contrasted to nonmagnetic olfactory cells, share ancestry with an ancient prokaryote magnetite biomineralization system, consistent with exaptation for use in eukaryotic magnetoreception. Certain bacteria produce magnetite crystals inside intracellular compartments, representing the most ancient form of biomineralization known and having evolved prior to emergence of the crown group of eukaryotes, raising the question of whether magnetite biomineralization in eukaryotes and prokaryotes might share a common evolutionary history. One idea is that geomagnetic fields are physically transduced by magnetite crystals contained inside specialized receptor cells, but evidence for intracellular, biogenic magnetite in eukaryotes is scant. Animals use geomagnetic fields for navigational cues, yet the sensory mechanism underlying magnetic perception remains poorly understood.
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