Release of digestive enzymes from the crustacean hepatopancreas: effect of vertebrate gastrointestinal hormones

Histological, Physiological and Transcriptomic Analysis Reveal the Acute Alkalinity Stress of the Gill and Hepatopancreas of Litopenaeus vannamei

The pacific white shrimp (Litopenaeus vannamei) has gradually become a promising economic species in the development of saline-alkali water fishery. The study related to the stress reaction of pacific white shrimp under alkalinity stress is still limited, which is also a critical limiting factor for its saline-alkaline aquaculture. In this study, we aim to analyse the stress reaction of pacific white shrimp under acute alkalinity stress between control group (alkalinity:40 mg/L) and treatment group (alkalinity:350 mg/L) through histological observation, physiological determination and transcriptome. In the present study, during the process of acute alkalinity stress, the activities of Na+-K+-ATPase, carbonic anhydrase, sodium/hydrogen exchanger in gill related to homeostasis were significantly changed, the activities of superoxide dismutase and catalase related to antioxidant were decreased in both gill and hepatopancreas, and the activities of protease, lipase and amylase in hepatopancreas were decreased. At the same time, different degrees of histological damages were occured in the gill and hepatopancreas under acute alkalinity stress. There were 194 and 236 different expressed genes identified in gill and hepatopancreas respectively. Functional enrichment assessment indicated that the alkalinity stress-related genes in both gill and hepatopancreas were primarily involved in fatty acid metabolism, glycolysis/gluconeogenesis, glycerophospholipid metabolism. The results indicated that the functions of homeostasis regulation, antioxidation and digestion of pacific white shrimp were decreased under acute alkalinity stress, at the same time, the energy metabolism in gill and hepatopancreas were modified to cope with alkalinity stress. This work provides important clues for understanding the response mechanism of pacific white shrimp under acute alkalinity stress.

Invasive investigation: uptake and transport of l-leucine in the gill epithelium of crustaceans

Many aquatic species are well known as extremely successful invaders. The green crab (Carcinus maenas) is an arthropod native to European waters; however, it is now known to be a globally invasive species. Recently, it was discovered that the C. maenas could transport nutrients in the form of amino acids across their gill from the surrounding environment, a feat previously thought to be impossible in arthropods. We compared the ability for branchial amino acid transport of crustacean's native to Canadian Pacific waters to that of the invasive C. maenas, determining if this was a novel pathway in an extremely successful invasive species, or a shared trait among crustaceans. Active transport of l-leucine was exhibited in C. maenas, Metacarcinus gracilis, Metacarcinus magister, and Cancer productus across their gill epithelia. Carcinus maenas exhibited the highest maximum rate of branchial l-leucine transport at 53.7 ± 6.24 nmolg-1 h-1, over twice the rate of two native Canadian crustaceans. We also examined the influence of feeding, gill specificity, and organ accumulation of l-leucine. Feeding events displayed a heavy influence on the branchial transport rate of amino acids, increasing l-leucine transport rates by up to 10-fold in C. maenas. l-leucine displayed a significantly higher accumulation rate in the gills of C. maenas compared to the rest of the body at 4.15 ± 0.78 nmolg-1 h-1, with the stomach, hepatopancreas, eyestalks, muscle tissue, carapace and heart muscle exhibiting accumulation under 0.15 nmolg-1 h-1. For the first time, the novel transport of amino acids in Canadian native arthropods is described, suggesting that branchial amino acid transport is a shared trait among arthropods, contrary to existing literature. Further investigation is required to determine the influence of environmental temperature and salinity on transport in each species to outline any competitive advantages of the invasive C. maenas in a fluctuating estuarine environment.

Toward a More Comprehensive View of α-Amylase across Decapods Crustaceans

Decapod crustaceans are a very diverse group and have evolved to suit a wide variety of diets. Alpha-amylases enzymes, responsible for starch and glycogen digestion, have been more thoroughly studied in herbivore and omnivore than in carnivorous species. We used information on the α-amylase of a carnivorous lobster as a connecting thread to provide a more comprehensive view of α-amylases across decapods crustaceans. Omnivorous crustaceans such as shrimps, crabs, and crayfish present relatively high amylase activity with respect to carnivorous crustaceans. Yet, contradictory results have been obtained and relatively high activity in some carnivores has been suggested to be a remnant trait from ancestor species. Here, we provided information sustaining that high enzyme sequence and overall architecture conservation do not allow high changes in activity, and that differences among species may be more related to number of genes and isoforms, as well as transcriptional and secretion regulation. However, recent evolutionary analyses revealed that positive selection might have also occurred among distant lineages with feeding habits as a selection force. Some biochemical features of decapod α-amylases can be related with habitat or gut conditions, while less clear patterns are observed for other enzyme properties. Likewise, while molt cycle variations in α-amylase activity are rather similar among species, clear relationships between activity and diet shifts through development cannot be always observed. Regarding the adaptation of α-amylase to diet, juveniles seem to exhibit more flexibility than larvae, and it has been described variation in α-amylase activity or number of isoforms due to the source of carbohydrate and its level in diets, especially in omnivore species. In the carnivorous lobster, however, no influence of the type of carbohydrate could be observed. Moreover, lobsters were not able to fine-regulate α-amylase gene expression in spite of large changes in carbohydrate content of diet, while retaining some capacity to adapt α-amylase activity to very low carbohydrate content in the diets. In this review, we raised arguments for the need of more studies on the α-amylases of less studied decapods groups, including carnivorous species which rely more on dietary protein and lipids, to broaden our view of α-amylase in decapods crustaceans.

Integrative analysis identifies the quality advantage and corresponding regulatory mechanism of paddy field-cultured crayfish (Procambarus clarkii)

Procambarus clarkii is the dominant economic variety of crayfish in China, and paddy field shrimp cultivation is an organic mode of traditional rice-fish cultivation, with paddy field shrimp being the country's prevailing aquatic product. However, little has been reported on the differences in meat quality and digestive ability between paddy field and pond fish. In this study, the muscle composition and digestive function regulation of P. clarkii in ponds and paddies were studied to explore the influence of paddy field culture on P. clarkii quality. The results showed that the muscle composition of paddy field shrimp was significantly changed, with increased protein and decreased lipid levels. Through the study of the hepatopancreas and intestinal microbial diversity of P. clarkii, we hypothesized that rice farming may cause changes in its bacterial spectrum, stimulate the digestive functions of its intestines and hepatopancreas, cause differential expression of multi-substance metabolic pathways, and ultimately result in the substances' deposition in its muscles. This study revealed the impact of rice cultivation on P. clarkii from the perspective of meta-metabolism, and it demonstrated the advantages of paddy field shrimp cultivation.Key points• We explored the influence of paddy field culture on P. clarkii quality.• Muscle composition of paddy field shrimp was significantly changed, with increased protein and decreased lipid levels in paddy field.• Rice farming caused changes in its bacterial spectrum and stimulated the digestive functions of hepatopancreas.

Synthesis of digestive enzymes, food processing, and nutrient absorption in decapod crustaceans: a comparison to the mammalian model of digestion

The ∼15.000 decapod crustaceans that are mostly omnivorous have evolved a structurally and functionally complex digestive system. They have highly effective cuticular chewing and filtering structures in the stomach, which are regularly renewed by moulting. Decapods produce a broad range of digestive enzymes including chitinases, cellulases, and collagenases with unique properties. These enzymes are synthesized in the F-cells of the hepatopancreas and are encoded in the genome as pre-pro-proteins. In contrast to mammals, they are stored in a mature form in the lumen of the stomach to await the next meal, and therefore, the enzymes are particularly stable. The fat emulsifiers are fatty acyl-dipeptides rather than bile salts. After mechanical and chemical processing of the food in the cardiac stomach, the chyme is filtered by two unique filter systems of different mesh-size. The filtrate is then transferred to the hepatopancreas where the nutrients are absorbed by the R-cells, mostly via carriers, resembling nutrient absorption in the small intestine of mammals. The absorbed nutrients are used to fuel the metabolism of the hepatopancreas, are supplied to other organs, and are stored in the R-cells as glycogen and lipid reserves. Export lipids are secreted from the R-cells into the haemolymph as high density lipoproteins that mainly consist of phospholipids. In contrast to mammals, the midgut tube and hindgut contribute only little to food processing and nutrient absorption. The oesophagus, stomach and hindgut are well innervated but the hepatopancreas lacks nerves. Hormone cells are abundant in the midgut and hepatopancreas epithelia. Microorganisms are often present in the intestine of decapods, but they are apparently not essential for digestion and nutrition.

Differential modulation after feeding in different salinities and response to abscisic acid (ABA) and extracellular Ca2+ of aminopeptidase N (APN) activity in the hepatopancreas of the intertidal euryhaline crab Neohelice granulata

Modulation of aminopeptidase N (APN) activity in the digestive tract by various factors would be important to adjust digestive and absorptive processes under different physiological and (or) environmental conditions. We studied the postprandial responses at different salinities and the effect of abscisic acid (ABA) and extracellular Ca2+ on APN activity in the hepatopancreas (the main site for nutrient digestion and absorption) of the model species Neohelice granulata (Dana, 1851). Enzyme activity was determined at different times (0, 24, 48, and 72 h) after feeding in crabs acclimated either to 35 psu (osmoconformation) or 10 psu (hyper-regulation). APN activity increased around 50% at 24 h after feeding at 35 psu, whereas no changes occurred at 10 psu. Enzyme activity was also assayed in the presence of ABA (1 × 10–4 mol·L–1) or extracellular Ca2+ (1 × 10–4 mol·L–1), showing increments of 60% and 56%, respectively. The results suggest a role of APN in postprandial adjustments and its modulation by different chemical messengers by direct effect on the hepatopancreas. Moreover, to our knowledge, this work is the first to show the effect of ABA on a digestive enzyme in the digestive tract of an animal.

Trypsin isozymes in the lobster Panulirus argus (Latreille, 1804): from molecules to physiology

Trypsin enzymes have been studied in a wide variety of animal taxa due to their central role in protein digestion as well as in other important physiological and biotechnological processes. Crustacean trypsins exhibit a high number of isoforms. However, while differences in properties of isoenzymes are known to play important roles in regulating different physiological processes, there is little information on this aspect for decapod trypsins. The aim of this review is to integrate recent findings at the molecular level on trypsin enzymes of the spiny lobster Panulirus argus, into higher levels of organization (biochemical, organism) and to interpret those findings in relation to the feeding ecology of these crustaceans. Trypsin in lobster is a polymorphic enzyme, showing isoforms that differ in their biochemical features and catalytic efficiencies. Molecular studies suggest that polymorphism in lobster trypsins may be non-neutral. Trypsin isoenzymes are differentially regulated by dietary proteins, and it seems that some isoenzymes have undergone adaptive evolution coupled with a divergence in expression rate to increase fitness. This review highlights important but poorly studied issues in crustaceans in general, such as the relation among trypsin polymorphism, phenotypic (digestive) flexibility, digestion efficiency, and feeding ecology.

Dietary protein quality differentially regulates trypsin enzymes at the secretion and transcription level in Panulirus argus by distinct signaling pathways

The effects of pelleted diets with different protein composition (fish, squid or soybean meals as main protein sources) on trypsin secretion and expression were studied in the lobster Panulirus argus. Trypsin secretion was shown to be maximal 4 h after ingestion. At this time, fish- and squid-based diets induced trypsin secretion, as well as up-regulation of the major trypsin isoform at the transcription level. While fish- and squid-based diets elicited a prandial response, soybean-based diet failed to stimulate the digestive gland to secrete trypsin into the gastric fluid or induce trypsin expression above the levels observed in fasting lobsters. In vitro assays showed that intact proteins rather than protein hydrolysates stimulate trypsin secretion in the lobster. However, the signal for trypsin transcription appears to be different to that for secretion and is probably mediated by the appearance of free amino acids in the digestive gland, suggesting a stepwise regulation of trypsin enzymes during digestion. We conclude that trypsin enzymes in P. argus are regulated at the transcription and secretion level by the quality of dietary proteins through two distinct signaling pathways. Our results indicate that protein digestion efficiency in spiny lobsters can be improved by selecting appropriated protein sources. However, other factors like the poor solubility of dietary proteins in dry diets could hamper further enhancement of digestion efficiency.

Cysteine and serine protease-mediated proteolysis in body homogenate of a zooplankter, Moina macrocopa, is inhibited by the toxic cyanobacterium, Microcystis aeruginosa PCC7806

The paper describes the characterization of proteases in the whole body homogenate of Moina macrocopa, which can possibly be inhibited by the extracts of Microcystis aeruginosa PCC7806. With the use of oligopeptide substrates and specific inhibitors, we detected the activities of trypsin, chymotrypsin, elastase and cysteine protease. Cysteine protease, the predominant enzyme behind proteolysis of a natural substrate, casein, was partially purified by gel filtration. The substrate SDS-polyacrylamide gel electrophoresis of body homogenate revealed the presence of nine bands of proteases (17-72 kDa). The apparent molecular mass of an exclusive cysteine protease was 60 kDa, whereas of trypsin, it was 17-24 kDa. An extract of M. aeruginosa PCC7806 significantly inhibited the activities of trypsin, chymotrypsin and cysteine protease in M. macrocopa body homogenate at estimated IC(50) of 6- to 79-microg dry mass mL(-1). Upon fractionation by C-18 solid-phase extraction, 60% methanolic elute contained all the protease inhibitors, and these metabolites could be further separated by reverse-phase liquid chromatography. The metabolites inhibitory to M. macrocopa proteases also inhibited the corresponding class of proteases of mammalian/plant origin. The study suggests that protease inhibition may contribute to chemical interaction of cyanobacteria and crustacean zooplankton.

Protease activity in gut of Daphnia magna: evidence for trypsin and chymotrypsin enzymes

Two major protease activities were present in gut homogenates of the cladoceran crustacean Daphnia magna: (i) a trypsin activity that hydrolysed the synthetic substrate N-benzoyl-dl-arginine p-nitroanilide and was strongly inhibited by N-p-tosyl-lysine chloroketone (TLCK) and 4-(amidinophenyl)methanesulfonyl fluoride (APMSF) and not inhibited by chymostatin; and (ii) a chymotrypsin activity that hydrolysed synthetic chymotrypsin substrates containing more than one amino acid, did not hydrolyse N-benzoyl-l-tyrosine p-nitroanilide, and was strongly inhibited by chymostatin and not by TLCK and APMSF. Both activities had alkaline pH optima (pH 7-10), but were shown to be due to distinct types of proteases. These two enzyme activities accounted for 75-83% of the proteolytic activity of gut contents. Substrate SDS-polyacrylamide gel electrophoresis revealed nine different proteases ranging from 15 to 73 kDa.

Toxic effects of microcystins in the hepatopancreas of the estuarine crab Chasmagnathus granulatus (Decapoda, Grapsidae)

Microcystins are toxins produced by cyanobacteria, being toxic to aquatic fauna. It was evaluated alternative mechanisms of microcystins toxicity, including oxidative stress and histopathology in the hepatopancreas of the estuarine crab Chasmagnathus granulatus (Decapoda, Grapsidae). Microcystins was administered to crabs (MIC group) over 1 week, whereas the control (CTR group) received the saline from cyanobacteria culture medium. At day 7, catalase activity was higher in the MIC than in the CTR group, although a decrease of activity was verified in both groups with respect to time 0. Glutathione-S-transferase activity augmented in MIC with respect to CTR, suggesting a higher conjugation rate of the toxins with glutathione. No differences were detected in the superoxide dismutase activity. Lipid peroxidation remained stable in both groups. Histopathological analyses showed that the number of B cells decreased significantly in the CTR as a possible effect of starvation, while no significant change was observed in the MIC group. The hepatopancreas from the MIC group exhibited some necrotic tubules and melanin-like deposits. Overall, results showed that some enzymes of the antioxidant defense system were activated after microcystins exposure, this response being able to maintain lipid peroxidation levels, but insufficient to completely prevent histological damage.

Isolation, identification, and synthesis of a disulfated sulfakinin from the central nervous system of an arthropods the white shrimp Litopenaeus vannamei

Two myotropic peptides displaying tyrosyl sulfation have been isolated from an extract of central nervous systems (brain, suboesophageal ganglion, thoracic ganglia, and ventral nerve cord) of the white shrimp Litopenaeus vannamei. Both peptides were identified by mass spectrometry and belong to the sulfakinin family of neuropeptides, which are characterized by the C-terminal hexapeptide Y(SO(3)H)GHMRF-NH(2) preceded by two acidic amino acid residues. Pev-SK 1 (AGGSGGVGGEY(SO(3)H)DDY(SO(3)H)GH(L/I) RF-NH(2)) has two sulfated tyrosyl residues and a unique (L/I) for M substitution in the C-terminal sequence. Pev-SK 2 (pQFDEY(SO(3)H)GHMRF-NH(2)) fully complies with the typical sulfakinin core sequence and is blocked by a pyroglutamyl residue. Synthetic analogs (sulfated and unsulfated) were synthesized and the tyrosyl sulfations were confirmed by myotropic activity studies and co-elution with the native fractions. Pev-SK 1 is the first disulfated neuropeptide elucidated in the phylum of the arthropoda, with the only other reported disulfated neuropeptide, called cionin, found in a protochordate. The similarities in amino acid sequence and posttranslational modifications of the crustacean sulfakinins and protochordate cionin provide further evidence for the hypothesis stating that gastrin/CCK, cionin, and sulfakinins originate from a common ancestral gastrin/CCK-like peptide.

Cloning and expression of a cDNA for a putative G protein-coupled receptor from the hepatopancreas of the crayfish, Procambarus clarkii

The authors cloned a novel cDNA encoding a putative G protein-coupled receptor (GPCR) from the hepatopancreas of the crayfish, Procambarus clarkii, using a screening approach with synthetic oligonucleotides. The oligonucleotides were designed homologous to the transmembrane spanning domain III of previously cloned receptors from various living organisms. Sequence analysis revealed that one of the positive clones contained a cDNA insertion of 3489 bp representing the mRNA coding for a part of a putative GPCR (termed HP1R). The clone was truncated at the 5' end. The long 3'-untranslated regions (UTR) of 2446 bp contained three typical AATAAA censensus sequences for mRNA polyadenylation followed by the poly(A) tail at the 3' end. To obtain a full-length cDNA clone, rapid amplification of the 5' cDNA ends (5' RACE) technique was then applied. Sequence analysis revealed that the full-length cDNA clone had an open-reading frame of 1116 bp with a 103-bp 5'-UTR. The predicted amino acid sequence of HP1R was 372 residues long. Hydropathicity analysis of HP1R suggested the presence of seven transmembrane domains. The database search revealed that the predicted sequence is most closely related to probable GPCR AH9.1 from Caenorhabditis elegans (27% identity, 48% homology). In addition, HP1R has lower homologies with receptors for somatostatin, opioid, dopamine, adrenalin, and so on. The similarity implied that HP1R is a new member of putative GPCRs whose endogenous ligands were unknown. In addition, RT-PCR analysis suggested that the transcript was expressed predominantly in the hepatopancreas but poorly in the muscle or brain.