Methionine-enkephalin induces hyperglycemia through eyestalk hormones in the estuarine crab Scylla serrata

Point-of-care testing for measuring haemolymph glucose in invertebrates is not a valid method

Blood glucose is widely used as a physiological parameter for vertebrates and invertebrates. However, its measurement in the field is often difficult due to the need for expensive and non-portable equipment. Point-of-care (POC) devices, originally intended for human use, are increasingly being used for measuring blood parameters of animals in the field. In this regard, POC glucose meters are becoming valuable tools for conservation physiologists, as glucose can be a useful indicator of stress response. In invertebrates, the use of POC glucose meters is still scarce, and no study yet has evaluated their usability in crustaceans and molluscs. We tested if a POC device can be used to measure haemolymph glucose in two widely used models, Leptuca thayeri and Perna perna, compared with a standard laboratory method. The device was unable to measure glucose in P. perna haemolymph due to equipment inaccuracy and low glucose concentration in this species (10.13 ± 6.25 mg/dL). Additionally, despite the device being capable of measuring glucose in L. thayeri haemolymph, Bland-Altman plots showed a strong bias and wide limits of agreement, and Lin's concordance correlation coefficient showed a weak concordance between methods. When simulating experimental conditions, POC results differed from those found using the standard method. We conclude that POC glucose meters are unsuitable for assessing glucose in mussels and should not be used in crabs as results are inaccurate.

Transcriptome analysis of hemocytes from the white shrimp Litopenaeus vannamei with the injection of dopamine

As a crucial neuroendocrine-immune factor, dopamine (DA) could regulate the immune system of Litopenaeus vannamei. To understand the immune mechanisms and regulatory pathways of DA in L. vannamei, the transcriptome analysis of hemocytes of L. vannamei with injection of DA (10^-6 mol/shrimp) at 3 and 12 h were performed in this study. Moreover, quantitative real-time PCR (qPCR) method was applied to validate the accuracy of transcriptome sequencing and analyze the expression pattern of candidate differentially expressed genes (DEGs) at different time points (0, 3, 6, 12, and 24 h) after DA injection. The results showed that a total of 51382 unigenes with a N50 length of 2341 bp were generated. And 1397 and 457 DEGs were obtained by comparative transcriptome at 3 and 12h respectively. Moreover, the results of functional annotation and enriched pathway showed that the DEGs were involved in phagosome (ko04145), lysosome (ko04142), Endocytosis (ko04144), and NOD-like receptor signaling pathway (ko04621). Besides, the Pearson's correlation coefficient (R) between transcriptome sequencing and qPCR was 0.845, which confirmed the reliability of the transcriptome sequencing results and the accuracy of assembly. Furthermore, the expression pattern of 15 candidate DEGs, containing 9 up-regulated and 6 down-regulated DEGs at 3 h, indicated the regulation of DA in physiological functions especially in the immune system. Therefore, these results revealed that DA induced the expressions of membrane receptors or proteins, activated intracellular signaling pathways, regulated cellular and humoral immune systems, controlled antioxidation and apoptosis, and was involved in the regulation of neuroendocrine system. These findings are helpful to promote the understanding on the effects of biogenic amines on physiological functions and regulatory networks of crustacean, and offer a substantial material and foundation for researching the immune response of crustacean.

CHH binding protein (CHHBP): a newly identified receptor of crustacean hyperglycemic hormone (CHH)

Crustacean hyperglycemic hormone (CHH) is a neurohormone found only in arthropods that plays a pivotal role in the regulation of hemolymph glucose levels, molting, and stress responses. Although it was determined that a membrane guanylyl cyclase (GC) acts as the CHH receptor in the Y-organ during ecdysteroidogenesis, the identity of the CHH receptor in the hepatopancreas has not been established. In this study, we identified a new molecular, CHH binding protein (CHHBP), as a potential receptor by screening the annotated unigenes from the transcriptome of Eriocheir sinensis, after removal of eyestalk. Analysis of the binding affinity between CHH and CHHBP provided direct evidence that CHH interacts with CHHBP in a specific binding mode. Subsequent analysis showed that CHHBP was expressed primarily in the hepatopancreas and localized on cell membrane. In addition, real-time PCR analysis showed that CHHBP transcript levels gradually increased in the hepatopancreas following eyestalk ablation. RNAi-mediated suppression of CHHBP expression resulted in decreased glucose levels. Furthermore, the reduction of blood glucose induced by CHHBP RNAi reached the same degree as that observed in the eyestalk ablation group, suggesting that CHHBP contributes to glucose metabolism regulated by CHH. Besides, compared to the control group, injection of CHH was unable to rescue the decreased glucose levels in CHHBP RNAi crabs. CHH induced transport of 2-NBDG to the outside of cells, with indispensable assist from CHHBP. Taken together, these findings imply that CHHBP probably acts as one type of the primary signal processor of CHH-mediated regulation of cellular glucose metabolism.

Changes in the organics metabolism in the hepatopancreas induced by eyestalk ablation of the Chinese mitten crab Eriocheir sinensis determined via transcriptome and DGE analysis

Background

To understand the regulation mechanism of eyestalk ablation on the activities of hepatopancreas, Illumina RNA-Seq and digital gene expression (DGE) analyses were performed to investigate the transcriptome of the eyestalk, Y-organ, and hepatopancreas of E. sinensis and to identify the genes associated with the hepatopancreas metabolism that are differentially expressed under eyestalk ablation conditions.

Results

A total of 58,582 unigenes were constructed from 157,168 contigs with SOAPdenovo. A BlastX search against the NCBI Nr database identified 21,678 unigenes with an E-value higher than 10⁻⁵. Using the BLAST2Go and BlastAll software programs, 6,883 unigenes (11.75% of the total) were annotated to the Gene Ontology (GO) database, 7,386 (12.6%) unigenes were classified into 25 Clusters of Orthologous Groups of Proteins (COGs), 16,200 (27.7%) unigenes were assigned to 242 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and1,846 unigenes were matched to “metabolism pathways”. The DGE analysis revealed that 1,416 unigenes were significantly differentially expressed in the hepatopancreas, of which 890 unigenes were up-regulated and 526 unigenes were down-regulated. Of the differentially expressed genes, 382 unigenes were annotated and 63 were classified into metabolism pathways. The results of the real-time polymerase chain reaction (PCR) analysis of four unigenes related to carbohydrate metabolism were consistent with those obtained from the DGE analysis, which demonstrates that the sequencing data were satisfactory for further gene expression analyses.

Conclusion

This paper reported the transcriptom of the eyestalk, Y-organ, and hepatopancreas from E. sinensis. DGE analysis provided the different expressed genes of the metabolism processes in hepatopancreas that are affected by eyestalk ablation. These findings will facilitate further investigations on the mechanisms of the metabolism of organic substances during development and reproduction in crustaceans.

Effects of crustacean hyperglycemic hormone (CHH) on the transcript expression of carbohydrate metabolism-related enzyme genes in the kuruma prawn, Marsupenaeus japonicus

Crustacean hyperglycemic hormone (CHH), a member of a neuropeptide family present only in arthropods, plays a pivotal role in the modulation of hemolymph glucose levels, molting, reproduction, and the stress response. Although it has been determined that hepatopancreas and muscle are the major tissues in which CHH regulates hyperglycemic activity, the molecular mechanism by which CHH regulates carbohydrate metabolism remains unclear. In this study, we analyzed the mRNA expression levels of enzymes involved in glycogen metabolism and gluconeogenesis in order to determine how CHH regulates hemolymph glucose levels. We first cloned cDNAs encoding four carbohydrate metabolism-related enzymes from the kuruma prawn, Marsupenaeus japonicus, glycogen phosphorylase (MjGP), glycogen synthase (MjGS), fructose 1,6-bisphosphatase (MjFBPase), and phosphoenolpyruvate carboxykinase (MjPEPCK). RT-PCR analysis showed that eyestalk ablation remarkably decreased MjGP and increased MjGS transcript levels in the hepatopancreas, but not in muscle. Considering the fact that various eyestalk factors, including MIH, are removed by eyestalk ablation, these results indicate that after eyestalk ablation the metabolic state proceeds towards glycogen accumulation in the specific tissues related to molting. In contrast, MjFBPase and MjPEPCK transcript levels were not significantly changed by eyestalk ablation, indicating that CHH and other eyestalk-derived factors might not induce gluconeogenesis. Quantitative real-time PCR analysis showed that exposure of hepatopancreas to recombinant CHH significantly changed the expression levels of MjGP and MjGS, but not MjFBPase and MjPEPCK. Collectively, these results indicate that CHH is involved in glycogen metabolism in hepatopancreas.

Crustacean neuropeptides

Crustaceans have long been used for peptide research. For example, the process of neurosecretion was first formally demonstrated in the crustacean X-organ-sinus gland system, and the first fully characterized invertebrate neuropeptide was from a shrimp. Moreover, the crustacean stomatogastric and cardiac nervous systems have long served as models for understanding the general principles governing neural circuit functioning, including modulation by peptides. Here, we review the basic biology of crustacean neuropeptides, discuss methodologies currently driving their discovery, provide an overview of the known families, and summarize recent data on their control of physiology and behavior.

Role of methionine-enkephalin on the regulation of carbohydrate metabolism in the rice field crab Oziotelphusa senex senex

In the present study, the role of eyestalks and involvement of methionine-enkephalin in the regulation of haemolymph sugar level was studied. Bilateral eyestalk ablation significantly decreased the haemolymph sugar levels, whereas injection of eyestalk extract into ablated crabs significantly increased the haemolymph sugar levels. Total carbohydrate (TCHO) and glycogen levels were significantly increased in hepatopancreas and muscle of eyestalk-ablated crabs, with a decrease in phosphorylase activity. Injection of eyestalk extract into ablated crabs resulted in partial/complete reversal of these changes. Injection of methionine-enkephalin into intact crabs significantly increased the haemolymph sugar level in a dose-dependent manner. Total tissue carbohydrate and glycogen levels were significantly decreased, with an increase in phosphorylase activity in hepatopancreas and muscle tissues of intact crabs after methionine-enkephalin injection. Methionine-enkephalin injection did not cause any changes in haemolymph sugar, tissue total carbohydrate and glycogen levels and activity levels of phosphorylase in eyestalk-ablated crabs. These results suggest that the eyestalks are the main source of hyperglycaemic hormone and methionine-enkephalin induces hyperglycaemia through eyestalks.

Hyperglycaemic effects of 5-hydroxytryptamine and dopamine in the freshwater prawn, Macrobrachium malcolmsonii

The effects of 5-hydroxytryptamine (5-HT; serotonin) and dopamine (DA) on tissue carbohydrate metabolism and haemolymph glucose levels in the freshwater prawn, Macrobrachium malcolmsonii, were investigated. Injection of 5-HT and DA produced hyperglycaemia in a dose-dependent and time-dependent manner, with DA being more effective than 5-HT. Interestingly, 5-HT and DA induced hyperglycaemia only in intact prawns but not in bilaterally eyestalk-ablated individuals. Total carbohydrate (TCHO) and glycogen levels decreased and phosphorylase activity increased in the hepatopancreas and muscle of intact prawns after being injected with 5-HT or DA. However, bilateral eyestalk ablation decreased haemolymph glucose and tissue phosphorylase activity and increased TCHO and glycogen levels of the hepatopancreas and muscle. Injection of 5-HT or DA did not cause significant changes in these variables in eyestalk-ablated prawns. It is hypothesized that 5-HT and DA induce hyperglycaemia in prawns by stimulating the release of crustacean hyperglycaemic hormone (CHH) from the X-organ sinus gland (XO-SG) complex located in the eyestalk.

Species-specific effects on hemolymph glucose control by serotonin, dopamine, and L-enkephalin and their inhibitors inSquilla mantis andAstacus leptodactylus (crustacea)

Hemolymph glucose level is controlled by crustacean Hyperglycemic Hormone (cHH) released from the eyestalk neuroendocrine centers under conditions of both physiological and environmental stress. Biogenic amines and enkephalin have been found to mediate the release of several neurohormones from crustacean neuroendocrine tissue. We investigated the effect of serotonin, dopamine, and Leucine-enkephalin in vivo--injected into the stomatopod Squilla mantis and the decapod Astacus leptodactylus--whether increasing or depressing glycemia. Serotonin had a marked effect in elevating glucose level compared with initial values in both species. 5-HT1-like receptors are more involved in mediating serotonin action as co-injected cyproheptadine was a more effective antagonist than ketanserin (5-HT2-like receptor inhibitor). Dopamine injection in intact animals produced a decrease below initial levels of hemolymph glucose. This effect was significantly antagonized by domperidone. No significant effect of both amines occurred in eyestalkless animals. L-enkephalin shows a differential effect: in S. mantis it induced hypoglycemia while in A. leptodactylus it caused an increase of glucose level. Co-injected antagonist naloxone affected the direction of the response. Serotonin appears to provide a major control on glucose mobilization, whereas dopamine and L-enkephalin act as modulators whose plasticity in use or action varies among species.