Abstract
Crustaceans express genes for at least three classes of putative chemosensory proteins. These are: Ionotropic Receptors (IRs), derived from the heterotetrameric ionotropic glutamate receptors (iGluRs); Transient Receptor Potential (TRP) channels, a diverse set of sensor-channels that include several families of chemoreceptor channels; and Gustatory Receptor Like receptors (GRLs), ionotropic receptors that are homologues of Gustatory Receptors (GRs) of insects and are expressed sparingly in most crustaceans so far studied. IRs are typically numerically the most dominant of these receptor proteins in crustaceans and include two classes: co-receptor IRs, which are necessary for making a functional receptor-channel; and tuning IRs, whose specific combination in the IR subunits in the heterotetramer confers chemical specificity. Previous work showed that the transcriptomes from two major chemosensory organs–the lateral flagellum of the antennule (LF) and the tips of the legs (dactyls)–of the Caribbean spiny lobster Panulirus argus express four co-receptor IRs and over 100 tuning IRs. In this paper, we examined and compared the transcriptomes from the LF and dactyls of P. argus and three other decapod crustaceans–the clawed lobster Homarus americanus, red swamp crayfish Procambarus clarkii, and the blue crab Callinectes sapidus. Each species has at least ca. 100 to 250 IRs, 1 to 4 GRLs, and ca. 15 TRP channels including those shown to be involved in chemoreception in other species. The IRs show different degrees of phylogenetic conservation: some are arthropod-conserved, others are pancrustacean-conserved, others appear to be crustacean-conserved, and some appear to be species-specific. Many IRs appear to be more highly expressed in the LF than dactyl. Our results show that decapod crustaceans express an abundance of genes for chemoreceptor proteins of different types, phylogenetic conservation, and expression patterns. An understanding of their functional roles awaits determining their expression patterns in individual chemosensory neurons and the central projections of those neurons.
Highlights
Sensing environmental chemicals is critical for animals because it informs them of the presence and location of important resources
The goal of the current study is to extend our analysis of chemoreceptor proteins of decapod crustaceans by studying three additional decapod species commonly used in studies of chemoreception: American lobster Homarus americanus, crayfish Procambarus clarkii, and blue crab Callinectes sapidus
We previously identified Ionotropic Receptors (IRs), Gustatory Receptor Like receptors (GRLs), and transient receptor potential (TRP) channels expressed in two chemosensory organs–lateral flagella (LF) and dactyl–of the Caribbean spiny lobster, P. argus, based on sequence homology to receptors in other species [11]
Summary
Sensing environmental chemicals is critical for animals because it informs them of the presence and location of important resources. The detection is performed by chemosensory cells, whose receptor proteins bind stimulus molecules which in turn lead to a cascade of transduction events that results in activation of those cells. Our understanding of these receptor proteins has significantly evolved since the discovery by Buck and Axel in 1991 [1] that a major class of chemoreceptor proteins in the rodent olfactory system are modified rhodopsin-like type A G-protein coupled receptors (GPCR), called Odorant Receptors (OR). Vertebrates have a different class of important though numerically less abundant chemoreceptor proteins–ionotropic receptors–which include transient receptor potential (TRP) channels, epithelial sodium channels (ENaC), and MS4A receptors [2]
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