Putative chemosensory receptors are differentially expressed in the sensory organs of male and female crown-of-thorns starfish, Acanthaster planci

Abstract

BackgroundChemosensation is a critical signalling process for all organisms and is achieved through the interaction between chemosensory receptors and their ligands. The Crown-of-thorns starfish, Acanthaster planci species complex (COTS), is a predator of coral polyps and Acanthaster cf. solaris is currently considered to be one of the main drivers of coral loss on the Great Barrier Reef in Queensland, Australia.ResultsThis study reveals the presence of putative variant Ionotropic Receptors (IRs) which are differentially expressed in the olfactory organs of COTS. Several other types of G protein-coupled receptors such as adrenergic, metabotropic glutamate, cholecystokinin, trace-amine associated, GRL101 and GPCR52 receptors have also been identified. Several receptors display male-biased expression within the sensory tentacles, indicating possible reproductive significance.ConclusionsMany of the receptors identified in this study may have a role in reproduction and are therefore key targets for further investigation. Based on their differential expression within the olfactory organs and presence in multiple tissues, it is possible that several of these receptor types have expanded within the Echinoderm lineage. Many are likely to be species-specific with novel ligand-binding affinity and a diverse range of functions. This study is the first to describe the presence of variant Ionotropic Glutamate Receptors in any Echinoderm, and is only the second study to investigate chemosensory receptors in any starfish or marine pest. These results represent a significant step forward in understanding the chemosensory abilities of COTS.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-5246-0) contains supplementary material, which is available to authorized users.

Comparison of transcriptomes from two chemosensory organs in four decapod crustaceans reveals hundreds of candidate chemoreceptor proteins

“…We did not find any evidence for ORs in crustaceans in our work. Another class of chemoreceptor proteins are GPCRs, which have been shown or suggested to function as chemoreceptor proteins in some protostomes [27][28][29][30]. We found many rhodopsin-like GPCRs in our decapod transcriptomes, but most could be identified as homologues of known classes of GPCRs that are not mammalian ORs, and to date we have not found expanded families of orphaned GPCRs as might be expected if they function as chemoreceptor proteins (M. Rump, M. Kozma, and C. Derby unpublished results).…”

“…GPCRs have not been identified as candidates in arthropods, although pheromone transduction in the hawkmoth Manduca sexta may be mediated by a metabotropic signal transduction cascade [26]. On the other hand, a large family of chemosensory GPCRs are found in nematodes, and also appear to be in gastropod and cephalopod molluscs and asteroid echinoderms [4,10,11,[27][28][29][30].…”

A new subfamily of ionotropic glutamate receptors unique to the echinoderms with putative sensory role

“…IR25a and IR8a were the first type of IRs associated with chemosensation and they show conserved expression in several protostome olfactory organs (Croset et al, 2010; Liu et al, 2010; Olivier et al, 2011; Stepanyan et al, 2004). Although absent from echinoderms, IRs are evolutionarily related to other metazoan iGluRs, suggesting potentially conserved functional overlap (Croset et al, 2010; Roberts et al, 2018). In echinoderms, the tentacles are important enervated and sensory organ appendages that allow the animals to move or to handle food (Cameron & Fankboner, 1984; Díaz‐Balzac et al, 2010; Hamel & Mercier, 2011) and expression of two homologues of vertebrate GluR2 (our GluA) and gKAR2 (our GluD) in the tentacles and tube feet of A. planci was taken to suggest involvement in chemosensation (Roberts et al, 2018).…”

Holothurians have a reduced GPCR and odorant receptor-like repertoire compared to other echinoderms

“…It is also important to note that chemosensory receptors other than GPCRs may also exist in sea cucumbers. For example, putative variant ionotropic glutamate receptors were recently discovered in the starfish A. planci 64 .…”