Expression of ionotropic receptors in terrestrial hermit crabs olfactory sensory neurons

Coenobitidae are one out of at least five crustacean lineages which independently succeeded in the transition from water to land. This change in lifestyle required various adaptations of their olfactory organs in order to sense chemical cues in the new conveying medium. The crustacean sense of smell is situated in their first pair of antennae, also called antennules, and more precisely in the olfactory aesthetascs that are arranged in a field on the distal segment of the antennular flagellum. Aesthetascs house approximately 300 dendrites each, with their neurons cell bodies arranged in spindle-like complexes of ca. 150 each. Aesthetascs of aquatic crustaceans are the place of odor uptake and IR co-receptors IR25a and IR93a have been shown to be expressed in olfactory sensory neurons (OSNs) of the antennules. Our goal was to reveal the expression of non-co-receptor IRs in the OSNs of Coenobita clypeatus, a terrestrial hermit crab, with RNA in situ hybridization and their distribution pattern in the antennules. We investigated an RNAseq dataset revealing 22 novel divergent IRs in the Coenobita antennules and designed RNA probes for three exemplary IRs displaying their expression in cells of the OSN cell body complexes.