Localized expression of the olfactory receptor genes in the olfactory organ of common minke whales

Baleen whales (Mysticeti) possess the necessary anatomical structures and genetic elements for olfaction. Nevertheless, the olfactory receptor gene (OR) repertoire has undergone substantial degeneration in the cetacean lineage following the divergence of Artiodactyla and Cetacea. The functionality of the highly degenerated mysticete ORs within their olfactory epithelium remains unknown. In this study, we extracted total RNA from the nasal mucosa of common minke whales ( Balaenoptera acutorostrata ) to investigate the localized expression of ORs. All three sections of the mucosae examined in the nasal chamber displayed comparable histological structure, whereas the posterior portion of the frontoturbinal region exhibit notably high expression of ORs and another gene specific to the olfactory mucosa. Neither the olfactory bulb nor the external skin exhibited expression of these genes. Although this species possesses four intact class-1 ORs, all the ORs expressed in the nasal mucosa belong to class-2, implying the loss of aversion to specific odorants. These anatomical and genomic analyses suggest that ORs are still responsible for olfaction within the nasal region of baleen whales, enabling them to detect desirable scents such as prey and potential mating partners.