Gene Expression of Candidate Chemoreceptor Protein Families in Transcriptomes of Two Major Chemosensory Organs and Brain in Decapod Crustaceans

Chemoreceptor proteins are necessary for animals to detect chemical signals and cues in their environment in a process known as chemical sensing. The diversity and number of chemoreceptor proteins have been characterized in many groups of animals, but few have studied the repertoire of chemoreceptor proteins expressed by decapod crustaceans. Crustaceans express at least three classes of putative chemoreceptor proteins. These are: Variant Ionotropic Receptors (IRs), derived from the ionotropic glutamate receptors (iGluRs); Transient Receptor Potential (TRP) channels, a diverse set of sensor-channels; and Gustatory Receptor Like receptors (GRLs), a family of ionotropic receptor proteins that are ancestral to Gustatory Receptors (GRs) of insects. IRs are typically the most numerically dominant of these receptor proteins in crustaceans. In order to identify families of candidate chemoreceptor proteins that are expressed by decapod crustaceans, I examined and compared transcriptomes from four decapod crustaceans that are established models of chemoreception: the Caribbean spiny lobster Panulirus argus, the clawed lobster Homarus americanus, the red swamp crayfish Procambarus clarkii, and the blue crab Callinectes sapidus. Transcriptomes were generated from: a) two major chemosensory organs, the lateral flagella of the antennules (LF) and dactyls of the walking legs (dactyl), of all four decapod crustaceans; and b) the supraesophageal ganglion (brain) of only three decapod crustaceans, P. argus, H. americanus, and P. clarkii. Each species expressed genes for at least ca. 100 to 250 IRs, ca. 15 TRP channels including those shown to be chemoreceptors in other species, and 1 to 4 GRLs. The IRs show different degrees of phylogenetic conservation: protostome-conserved, arthropod-conserved, pancrustacean-conserved, crustacean-conserved, and species-specific. Many IRs appear to be more highly expressed in the LF than dactyl. In the brain transcriptomes, few IRs, almost all TRP channels, and GRLs (in the case of H. americanus) were also detected. Immunocytochemistry in LF and dactyl of P. argus and H. americanus, revealed protein expression of co-receptor IR, IR25a, in olfactory sensory neurons and chemosensory neurons. This research lays the foundation for future functional studies by showing that decapod crustaceans have an abundance of gene expression for chemoreceptor proteins of different types, phylogenetic conservation, and expression patterns