Roberts RE et al. (2018), Putative chemosensory receptors are differentia...

ECB-ART-46792

BMC Genomics 2018 Nov 29;191:853. doi: 10.1186/s12864-018-5246-0.

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

Roberts RE , Powell D , Wang T , Hall MH , Motti CA , Cummins SF .

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BACKGROUND: Chemosensation 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. RESULTS: This 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. CONCLUSIONS: Many 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.

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Species referenced: Echinodermata
Genes referenced: dclre1b LOC100890677 LOC100891068 LOC100893907 LOC105442694 LOC105444438 LOC115922105 LOC115926386 LOC579746 LOC583082 LOC594566 LOC762804 opn5

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	Fig. 1. Heatmaps showing differential gene expression in comparisons 1 to 3. a Female ST versus male ST (STF vs. STM). b Female TF versus male TF (TFF vs. TFM). c Combined male/female ST versus combined male/female TF (TFALL vs. STALL)
	Fig. 2. ApOR log2FC values within comparison 3 displaying under- and over-expression in COTS olfactory organs
	Fig. 3. Differential expression of the three receptor genes, a G protein-coupled receptor 52 (GPCR 52), an Alpha-1A adrenergic receptor-like (ADRA1A) and a metabotropic glutamate receptor 3 (mGluR3), within set 1 (a) Log2FC gene overexpression in male COTS sensory tentacle (ST). b Gene expression (TPM) in multiple COTS tissues: female sensory tentacle (STF), female tube foot (TFF), male tube foot (TFM) male radial nerve (RNM), female radial nerve (RNF), male spine (SPM), male mouth (MOM), testis (TE), early gastrula (EG), mid gastrula (MG), oocyte (OC). c Agarose gel electrophoresis of RT-PCR amplicons for 3 differentially expressed genes in multiple tissues from two pooled male and two pooled female COTS. Tissues: tube foot (TF), sensory tentacle (ST), radial nerve (RN), cardiac stomach (CS), body wall (BW), negative control (Neg). bp, base pairs
	Fig. 4. Differential gene expression of eight receptor genes within set 3, Glutamate receptor kainite 2-like (gKAR2), Glutamate receptor 2-like (GluR2), Trace amine-associated receptor 13c-like (TAAR13c), G protein-coupled receptor GRL101-like (GRL101), Cholecystokinin receptor type A-like (CCKRa), Metabotropic glutamate receptor 7 (mGluR7), and two isoforms of Alpha-1D adrenergic receptor-like (ADRA1D-like isoform X1 and ADRA1D-like isoform X2). a Log2FC gene overexpression in male COTS sensory tentacle (ST). b Gene expression in multiple COTS tissues: female sensory tentacle (STF), female tube foot (TFF), male tube foot (TFM) male radial nerve (RNM), female radial nerve (RNF), male spine (SPM), male mouth (MOM), testis (TE), early gastrula (EG), mid gastrula (MG), oocyte (OC). c Agarose gel electrophoresis of RT-PCR amplicons for eight differentially expressed genes in multiple tissues from two pooled male and two pooled female COTS. Tissues: tube foot (TF), sensory tentacle (ST), radial nerve (RN), cardiac stomach (CS), body wall (BW), negative control (Neg). bp, base pairs
	Fig. 5. Maximum likelihood phylogenetic analysis of iGluRs and IRs. COTS transcripts annotated as gKAR2 and GluR2 are indicated with blue circles. Conserved IRs are indicated by red lines, gKAR2 (kainite receptors) are indicated by green, GluR2 (AMPA receptors) are indicated by light blue, GluN (NMDA receptors) are indicated by yellow
	Fig. 6. Neighbour-joining phylogenetic analysis of adrenergic receptor protein sequences (ADRs). Alpha 1 ADRs, including subfamilies 1A, 1B and 1C are represented by red lines, alpha 2 ADRs, including subfamilies 2A, 2B and 2C are represented by yellow lines, and beta ADRs, including subfamilies 1, 2 and 3 are represented by purple lines. COTS sequences are represented by dark blue circles, COTS sequences that have previously been discovered to be ApORs are represented by light blue diamonds. Strongylocentrotus purpuratus sequences are represented by green circles. Differentially expressed sequences in COTS are indicated by black arrows

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