Differences in Small Molecule Neurotransmitter Profiles From the Crown-of-Thorns Seastar Radial Nerve Revealed Between Sexes and Following Food-Deprivation

The Development and Full Validation of a Novel Liquid Chromatography Electrochemical Detection Method for Simultaneous Determination of Nine Catecholamines in Rat Brain

Objectives

Chemical neurotransmission, managed by neurotransmitters, has a crucial role in brain processes such as fear, memory, learning, and pain, or neuropathology such as schizophrenia, epilepsy, anxiety/depression, and Parkinson's disease. The measurement of these compounds is used to elucidate the disease mechanisms and evaluate the outcomes of therapeutic interventions. However, this can be quite difficult because of various matrix effects and the problems of chromatographic separation of analysts. In the current study; for the first time, an optimized and fully validated high-performance liquid chromatography-electrochemical detection (HPLC-EC) method according to Food and Drug Administration and European Medicines Agency Bioanalytical Validation Guidance was developed for the simultaneous analysis of nine neurotransmitter compounds, namely dopamine, homovanilic acid, vanilmandelic acid, serotonin (SER), 5-hydroxyindole-3-acetic acid, 4-hydroxy-3-methoxyphenylglycol, norepinephrine, 3,4 dihydroxyphenylacetic acid, and 3-methoxytyramine and simultaneously determined in rat brain samples.

Materials and Methods

Separation was achieved with 150 mm x 4.6 mm, 2.6 μm Kinetex F5 (Phenomenex, USA) column isocratically, and analysis was carried out by HPLC equipped with a DECADE II EC detector.

Results

The method exhibited good selectivity, and the correlation coefficient values for each analyte's calibration curves were > 0.99. The detection and quantification limits ranged from 0.01 to 0.03 ng/mL and 3.04 to 9.13 ng/mL, respectively. The stability of the analyses and method robustness were also examined in detail in the study, and the obtained results are presented statistically.

Conclusion

The developed and fully validated method has been successfully applied to actual rat brain samples, and important results have been obtained. In the rat brain sample analysis, the lowest number of SER and the highest amount of noradrenaline were found.

Crown-of-thorns starfish spines secrete defence proteins

Background

The crown-of-thorns starfish (COTS; Acanthaster species) is a slow-moving corallivore protected by an extensive array of long, sharp toxic spines. Envenomation can result in nausea, numbness, vomiting, joint aches and sometimes paralysis. Small molecule saponins and the plancitoxin proteins have been implicated in COTS toxicity.

Methods

Brine shrimp lethality assays were used to confirm the secretion of spine toxin biomolecules. Histological analysis, followed by spine-derived proteomics helped to explain the source and identity of proteins, while quantitative RNA-sequencing and phylogeny confirmed target gene expression and relative conservation, respectively.

Results

We demonstrate the lethality of COTS spine secreted biomolecules on brine shrimp, including significant toxicity using aboral spine semi-purifications of >10 kDa (p > 0.05, 9.82 µg/ml), supporting the presence of secreted proteins as toxins. Ultrastructure observations of the COTS aboral spine showed the presence of pores that could facilitate the distribution of secreted proteins. Subsequent purification and mass spectrometry analysis of spine-derived proteins identified numerous secretory proteins, including plancitoxins, as well as those with relatively high gene expression in spines, including phospholipase A2, protease inhibitor 16-like protein, ependymin-related proteins and those uncharacterized. Some secretory proteins (e.g., vitellogenin and deleted in malignant brain tumor protein 1) were not highly expressed in spine tissue, yet the spine may serve as a storage or release site. This study contributes to our understanding of the COTS through functional, ultrastructural and proteomic analysis of aboral spines.

Biochemical metabolomic profiling of the Crown-of-Thorns Starfish (Acanthaster): New insight into its biology for improved pest management

The Crown-of-Thorns Starfish (COTS), Acanthaster species, is a voracious coral predator that destroys coral reefs when in outbreak status. The baseline metabolite and lipid biomolecules of 10 COTS tissues, including eggs from gravid females, were investigated in this study to provide insight into their biology and identify avenues for control. Targeted and untargeted metabolite- and lipidomics-based mass spectrometry approaches were used to obtain tissue-specific metabolite and lipid profiles. Across all COTS tissues, 410 metabolites and 367 lipids were identified. Most abundant were amino acids and peptides (18.7%) and wax esters (17%). There were 262 metabolites and 192 lipids identified in COTS eggs. Wax esters were more abundant in the eggs (30%) followed by triacylglycerols (TG), amino acids, and peptides. The diversity of asterosaponins in eggs (34) was higher than in tissues (2). Several asterosaponins known to modulate sperm acrosome reaction were putatively identified, including glycoside B, asterosaponin-4 (Co-Aris III), and regularoside B (asterosaponin A). The saponins saponin A, thornasteroside A, hillaside B, and non-saponins dictyol J and axinellamine B which have been shown to possess defensive properties, were found in abundance in gonads, skin, and radial nerve tissues. Inosine and 2-hexyldecanoic acid are the most abundant metabolites in tissues and eggs. As a secondary metabolite of purine degradation, inosine plays an important role in purine biosynthesis, while 2-hexyldecanoic acid is known to suppress side-chain crystallization during the synthesis of amphiphilic macromolecules (i.e., phospholipids). These significant spatial changes in metabolite, lipid, and asterosaponin profiles enabled unique insights into key biological tissue-specific processes that could be manipulated to better control COTS populations. Our findings highlight COTS as a novel source of molecules with therapeutic and cosmetic properties (ceramides, sphingolipids, carnosine, and inosine). These outcomes will be highly relevant for the development of strategies for COTS management including chemotaxis-based biocontrol and exploitation of COTS carcasses for the extraction of commercial molecules.

Analyses of regulatory network and discovery of potential biomarkers for Korean rockfish (Sebastes schlegelii) in responses to starvation stress through transcriptome and metabolome

Whether in aquaculture or in nature, starvation stress limits the growth of fish. The purpose of the study was to clarify the detailed molecular mechanisms underlying starvation stress in Korean rockfish (Sebastes schlegelii) through liver transcriptome and metabolome analysis. Transcriptome results showed that liver genes associated with cell cycle and fatty acid synthesis were down-regulated, whereas those related to fatty acid decomposition were up-regulated in the experimental group (EG; starved for 72 days) compared to the control group (CG; feeding). Metabolomic results showed that there were significant differences in the levels of metabolites related to nucleotide metabolism and energy metabolism, such as purine metabolism, histidine metabolism and oxidative phosphorylation. Five fatty acids (C22:6n-3; C22:5n-3; C20:5n-3; C20:4n-3; C18:3n-6) were selected as possible biomarkers of starvation stress from the differential metabolites of metabolome. Subsequently, correlation between these differential genes of lipid metabolism and cell cycle and differential metabolites were analyzed, and observed that these five fatty acids were significantly correlated with the differential genes. These results provide new clues for understanding the role of fatty acid metabolism and cell cycle in fish under starvation stress. It also provides a reference for promoting the biomarker identification of starvation stress and stress tolerance breeding research.

A New Model Organism to Investigate Extraocular Photoreception: Opsin and Retinal Gene Expression in the Sea Urchin Paracentrotus lividus

Molecular research on the evolution of extraocular photoreception has drawn attention to photosensitive animals lacking proper eye organs. Outside of vertebrates, little is known about this type of sensory system in any other deuterostome. In this study, we investigate such an extraocular photoreceptor cell (PRC) system in developmental stages of the sea urchin Paracentrotus lividus. We provide a general overview of the cell type families present at the mature rudiment stage using single-cell transcriptomics, while emphasizing the PRCs complexity. We show that three neuronal and one muscle-like PRC type families express retinal genes prior to metamorphosis. Two of the three neuronal PRC type families express a rhabdomeric opsin as well as an echinoderm-specific opsin (echinopsin), and their genetic wiring includes sea urchin orthologs of key retinal genes such as hlf, pp2ab56e, barh, otx, ac/sc, brn3, six1/2, pax6, six3, neuroD, irxA, isl and ato. Using qPCR, in situ hybridization, and immunohistochemical analysis, we found that the expressed retinal gene composition becomes more complex from mature rudiment to juvenile stage. The majority of retinal genes are expressed dominantly in the animals’ podia, and in addition to the genes already expressed in the mature rudiment, the juvenile podia express a ciliary opsin, another echinopsin, and two Go-opsins. The expression of a core of vertebrate retinal gene orthologs indicates that sea urchins have an evolutionarily conserved gene regulatory toolkit that controls photoreceptor specification and function, and that their podia are photosensory organs.

A Crown-of-Thorns Seastar recombinant relaxin-like gonad-stimulating peptide triggers oocyte maturation and ovulation

The Acanthaster planci species-complex [Crown-of-Thorns Seastar (COTS)] are highly fecund echinoderms that exhibit population outbreaks on coral reef ecosystems worldwide, including the Australian Great Barrier Reef. A better understanding of the COTS molecular biology is critical towards efforts in controlling outbreaks and assisting reef recovery. In seastars, the heterodimeric relaxin-like gonad stimulating peptide (RGP) is responsible for triggering a neuroendocrine cascade that regulates resumption of oocyte meiosis prior to spawning. Our comparative RNA-seq analysis indicates a general increase in RGP gene expression in the female radial nerve cord during the reproductive season. Also, the sensory tentacles demonstrate a significantly higher expression level than radial nerve cord. A recombinant COTS RGP, generated in a yeast expression system, is highly effective in inducing oocyte germinal vesicle breakdown (GVBD), followed by ovulation from ovarian fragments. The findings of this study provide a foundation for more in-depth molecular analysis of the reproductive neuroendocrine physiology of the COTS and the RGP.