Expression of arginine kinase enzymatic activity and mRNA in gills of the euryhaline crabs Carcinus maenas and Callinectes sapidus

Transcriptome-proteome compendium of the Antarctic krill (Euphausia superba): Metabolic potential and repertoire of hydrolytic enzymes

The Antarctic krill (Euphausia superba Dana) is a keystone species in the Southern Ocean that uses an arsenal of hydrolases for biomacromolecule decomposition to effectively digest its omnivorous diet. The present study builds on a hybrid-assembled transcriptome (13,671 ORFs) combined with comprehensive proteome profiling. The analysis of individual krill compartments allowed detection of significantly more different proteins compared to that of the entire animal (1,464 vs. 294 proteins). The nearby krill sampling stations in the Bransfield Strait (Antarctic Peninsula) yielded rather uniform proteome datasets. Proteins related to energy production and lipid degradation were particularly abundant in the abdomen, agreeing with the high energy demand of muscle tissue. A total of 378 different biomacromolecule hydrolysing enzymes were detected, including 250 proteases, 99 CAZymes, 14 nucleases and 15 lipases. The large repertoire in proteases is in accord with the protein-rich diet affiliated with E. superba's omnivorous lifestyle and complex biology. The richness in chitin-degrading enzymes allows not only digestion of zooplankton diet, but also the utilization of the discharged exoskeleton after moulting. This article is protected by copyright. All rights reserved.

Nutrition and Functions of Amino Acids in Aquatic Crustaceans

Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptides is essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, H₂S, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.

Structure and functional analysis reveal an important regulated role of arginine kinase in Patinopecten yessoensis under low pH stress

Arginine kinase (AK), an important member of the phosphokinase family, is involved in temporal and spatial adenosine triphosphate (ATP) buffering systems. AK plays an important role in physiological function and metabolic regulations, in particular tissues with high and fluctuating energy demands. In present study, four AK genes were firstly identified from Yesso scallop (Patinopecten yessoensis) genome, respectively named PyAK1-4. PyAKs have highly conserved structures with a six-exon/five-exon structure, except for PyAK3. PyAK3 contains an unusual two-domain structure and a "bridge intron" between the two domains, which may originate from gene duplication and subsequent fusion. Phylogenetic analysis showed that all PyAKs belonged to an AK supercluster together with other AK proteins from Mollusca, Platyhelminthes, Arthropoda, and Nematode. A transcriptome database demonstrated that PyAK3 and PyAK4 were the main functional executors with high expression level during larval development and in adult tissues, while PyAK1 and PyAK2 were expressed at a low level. Furthermore, both PyAK2 and PyAK3 showed notably high expression in the male gonad, and PyAK4 was broadly expressed in almost all tissues with the highest level in striated muscle, indicating a tissue-specific expression pattern of PyAKs. In addition, quantitative real-time PCR results demonstrated that the expression of PyAK2, PyAK3 and PyAK4 were significantly upregulated in response to pH stress, especially in an extremely acidifying condition (pH 6.5), revealing the possible involvement of PyAKs in energetic homeostasis during environmental changes. Collectively, a comprehensive analysis of PyAKs was conducted in P. yessoensis. The diversity of PyAKs and their specific expression patterns promote a better understanding of energy metabolism in the growth, development and environmental response of P. yessoensis.

Toll-like receptors (TLRs) respond to tributyltin chloride (TBT-Cl) exposure in the river pufferfish (Takifugu obscurus): Evidences for its toxic injury function

Tributyltin chloride (TBT-Cl) residual in water body had become a noticeable ecological problem for aquatic ecosystems. Toll-like receptors (TLRs) are an ancient family of pattern recognition receptors that play key roles in detecting nonself antigens and immune system activation. In this study, we explored the effect of TBT-Cl exposure on four TLRs expression in river pufferfish, Takifugu obscurus. The four T. obscurus Toll-like receptors (To-TLRs) contained different types of domains such as leucine-rich repeats (LRRs), leucine-rich repeats, typical subfamily (LRR_TYP) and other special domains. The To-TLRs mRNA transcripts expressed in all tissues, also To-TLR2 was investigated with higher level in kidney, as well as To-TLR3 in kidney, while To-TLR18 in liver and To-TLR22 in intestine. After the acute and chronic exposure of TBT-Cl, To-TLR2 and To-TLR3 mRNA transcripts were significantly down-regulated in gill. However, To-TLR18 and To-TLR22 were significantly up-regulated in gill and liver. Moreover, the histology and immunohistochemistry (IHC) results showed the different injury degrees of TBT-Cl in liver and gill and implied the cytoplasm reorganization after TBT-Cl stress and the function of immunoregulation for To-TLRs to TBT-Cl exposure. All the results indicated that To-TLRs might involve in sensing and mediating innate immune responses caused by TBT-Cl for keeping detoxification homeostasis.

Water bicarbonate modulates the response of the shore crab Carcinus maenas to ocean acidification

Ocean acidification causes an accumulation of CO₂ in marine organisms and leads to shifts in acid-base parameters. Acid-base regulation in gill breathers involves a net increase of internal bicarbonate levels through transmembrane ion exchange with the surrounding water. Successful maintenance of body fluid pH depends on the functional capacity of ion-exchange mechanisms and associated energy budget. For a detailed understanding of the dependence of acid-base regulation on water parameters, we investigated the physiological responses of the shore crab Carcinus maenas to 4 weeks of ocean acidification [OA, P(CO₂)_w = 1800 µatm], at variable water bicarbonate levels, paralleled by changes in water pH. Cardiovascular performance was determined together with extra-(pH_e) and intracellular pH (pH_i), oxygen consumption, haemolymph CO₂ parameters, and ion composition. High water P(CO₂) caused haemolymph P(CO₂) to rise, but pH_e and pH_i remained constant due to increased haemolymph and cellular [HCO₃^-]. This process was effective even under reduced seawater pH and bicarbonate concentrations. While extracellular cation concentrations increased throughout, anion levels remained constant or decreased. Despite similar levels of haemolymph pH and ion concentrations under OA, metabolic rates, and haemolymph flow were significantly depressed by 40 and 30%, respectively, when OA was combined with reduced seawater [HCO₃^-] and pH. Our findings suggest an influence of water bicarbonate levels on metabolic rates as well as on correlations between blood flow and pH_e. This previously unknown phenomenon should direct attention to pathways of acid-base regulation and their potential feedback on whole-animal energy demand, in relation with changing seawater carbonate parameters.

Metabolic responses and arginine kinase expression of juvenile cuttlefish (Sepia pharaonis) under salinity stress

The pharaoh cuttlefish Sepia pharaonis is particularly sensitive to environmental changes in its breeding environment. The breeding of S. pharaonis larvae was carried out in different salinities for 48h, and the changes in survival rate, histological structure, energy metabolism, and anti-oxidative stress parameters were investigated and correlated with arginine kinase (AK) expression changes in muscle and liver tissues. The suitable salinity for larvae cultivation ranged from 24 to 30‰, and the survival rate showed a significant decline at 21‰ salinity. Histological observations of muscle and liver showed that changes in salinity and osmotic pressure had an adverse effect on tissue structure. Measurements of glycogen and lactic acid levels suggested that S. pharaonis could dynamically adjust energy metabolism to provide additional energy under unsuitable salinity. The protein levels and enzyme activities of AK in muscle significantly increased at 21‰ salinity. The results were consistent with prompt replenishment of phosphoarginine stores during salinity stress to maintain a dynamic ATP balance, suggesting that AK plays an important role in the regulation of energy metabolism. This study provides insight into metabolic changes during salinity stress and sheds light on the functional role of AK in S. pharaonis.

Arginine kinase from Haemonchus contortus decreased the proliferation and increased the apoptosis of goat PBMCs in vitro

BACKGROUND

Arginine kinase (AK), an important member of phosphagen kinase family has been extensively studied in various vertebrates and invertebrates. Immunologically, AKs are important constituents of different body parts, involved in various biological and cellular functions, and considered as immune-modulator and effector for pro-inflammatory cytokines. However, immunoregulatory changes of host cells triggered by AK protein of Haemonchus contortus, a parasitic nematode of ruminants, are still unknown. The current study was focused on cloning and characterisation of Hc-AK, and its regulatory effects on cytokines level, cell migration, cell proliferation, nitric oxide production and apoptosis of goat peripheral blood mononuclear cells (PBMCs) were observed.

METHODS

The full-length sequence of the Hc-AK gene was amplified by reverse transcription-polymerase chain reaction (RT-PCR) and sub-cloned into the prokaryotic expression vector pET-32a. The biochemical characteristics of recombinant protein Hc-AK, which was purified by affinity chromatography, were performed based on the enzymatic assay. Binding of rHc-AK with PBMCs was confirmed by immunofluorescence assay (IFA). Immunohistochemical analysis was used to detect localisation of Hc-AK within adult worms sections. The immunoregulatory effects of rHc-AK on cytokine secretions, cell proliferation, cell migration, nitric oxide production and apoptosis were determined by co-incubation of rHc-AK with goat PBMCs.

RESULTS

The full-length ORF (1080 bp) of the Hc-AK gene was successfully cloned, and His-tagged AK protein was expressed in the Escherichia coli strain BL21. The recombinant protein of Hc-AK (rHc-AK) was about 58.5 kDa together with the fused vector protein of 18 kDa. The biochemical assay showed that the protein encoded by the Hc-ak exhibited enzymatic activity. Western blot analysis confirmed that the rHc-AK was recognised by the sera from rat (rat-antiHc-AK). The IFA results showed that rHc-AK could bind on the surface of goat PBMCs. Immunohistochemically, Hc-AK was localised at the inner and outer membrane as well as in the gut region of adult worms. The binding of rHc-AK to host cells increased the levels of IL-4, IL-10, IL-17, IFN-γ, nitric oxide (NO) production and cell apoptosis of goat PBMCs, whereas, TGF-β1 levels, cell proliferation and PBMCs migration were significantly decreased in a dose dependent manner.

CONCLUSIONS

Our findings suggested that rHc-AK is an important excretory and secretory (ES) protein involved in host immune responses and exhibit distinct immunomodulatory properties during interaction with goat PBMCs.

A transcriptomic scan for potential candidate genes involved in osmoregulation in an obligate freshwater palaemonid prawn (Macrobrachium australiense)

Background

Understanding the genomic basis of osmoregulation (candidate genes and/or molecular mechanisms controlling the phenotype) addresses one of the fundamental questions in evolutionary ecology. Species distributions and adaptive radiations are thought to be controlled by environmental salinity levels, and efficient osmoregulatory (ionic balance) ability is the main mechanism to overcome the problems related to environmental salinity gradients.

Methods

To better understand how osmoregulatory performance in freshwater (FW) crustaceans allow individuals to acclimate and adapt to raised salinity conditions, here we (i), reviewed the literature on genes that have been identified to be associated with osmoregulation in FW crustaceans, and (ii), performed a transcriptomic analysis using cDNA libraries developed from mRNA isolated from three important osmoregulatory tissues (gill, antennal gland, hepatopancreas) and total mRNA from post larvae taken from the freshwater prawn, Macrobrachium australiense using Illumina deep sequencing technology. This species was targeted because it can complete its life cycle totally in freshwater but, like many Macrobrachium sp., can also tolerate brackish water conditions and hence should have genes associated with tolerance of both FW and saline conditions.

Results

We obtained between 55.4 and 65.2 million Illumina read pairs from four cDNA libraries. Overall, paired end sequences assembled into a total of 125,196 non-redundant contigs (≥200 bp) with an N50 length of 2,282 bp and an average contig length of 968 bp. Transcriptomic analysis of M. australiense identified 32 different gene families that were potentially involved with osmoregulatory capacity. A total of 32,597 transcripts were specified with gene ontology (GO) terms identified on the basis of GO categories. Abundance estimation of expressed genes based on TPM (transcript per million) ≥20 showed 1625 transcripts commonly expressed in all four libraries. Among the top 10 genes expressed in four tissue libraries associated with osmoregulation, arginine kinase and Na+/K+- ATPase showed the highest transcript copy number with 7098 and 660, respectively in gill which is considered to be the most important organ involved in osmoregulation.

Discussion

The current study provides the first broad transcriptome from M. australiense using next generation sequencing and identifies potential candidate genes involved in salinity tolerance and osmoregulation that can provide a foundation for investigating osmoregulatory capacity in a wide variety of freshwater crustaceans.

Analysis, characterisation and expression of gill-expressed carbonic anhydrase genes in the freshwater crayfish Cherax quadricarinatus

Changes in water quality parameters such as pH and salinity can have a significant effect on productivity of aquaculture species. Similarly, relative osmotic pressure influences various physiological processes and regulates expression of a number of osmoregulatory genes. Among those, carbonic anhydrase (CA) plays a key role in systemic acid-base balance and ion regulation. Redclaw crayfish (Cherax quadricarinatus) are unique in their ability to thrive in environments with naturally varied pH levels, suggesting unique adaptation to pH stress. To date, however, no studies have focused on identification and characterisation of CA or other osmoregulatory genes in C. quadricarinatus. Here, we analysed the redclaw gill transcriptome and characterized CA genes along with a number of other key osmoregulatory genes that were identified in the transcriptome. We also examined patterns of gene expression of these CA genes when exposed to three pH treatments. In total, 72,382,710 paired end Illumina reads were assembled into 36,128 contigs with an average length of 800bp. Approximately 37% of contigs received significant BLAST hits and 22% were assigned gene ontology terms. Three full length CA isoforms; cytoplasmic CA (ChqCAc), glycosyl-phosphatidylinositol-linked CA (ChqCAg), and β-CA (ChqCA-beta) as well as two partial CA gene sequences were identified. Both partial CA genes showed high similarity to ChqCAg and appeared to be duplicated from the ChqCAg. Full length coding sequences of Na(+)/K(+)-ATPase, V-type H(+)-ATPase, sarcoplasmic Ca(+)-ATPase, arginine kinase, calreticulin and Cl(-) channel protein 2 were also identified. Only the ChqCAc gene showed significant differences in expression across the three pH treatments. These data provide valuable information on the gill expressed CA genes and their expression patterns in freshwater crayfish. Overall our data suggest an important role for the ChqCAc gene in response to changes in pH and in systemic acid-base balance in freshwater crayfish.

Digital gene expression analysis in hemocytes of the white shrimp Litopenaeus vannamei in response to low salinity stress

The white shrimp Litopenaeus vannamei has been greatly impacted by low salinity stress. To gain knowledge on the immune response in L. vannamei under such stress, we investigated digital gene expression (DEG) in L. vannamei hemocytes using the deep-sequencing platform Illumina HiSeq 2000. In total, 38,155 high quality unigenes with average length 770 bp were generated; 145 and 79 genes were identified up- or down-regulated, respectively. Functional categorization and pathways of the differentially expressed genes revealed that immune signaling pathways, cellular immunity, humoral immunity, apoptosis, cellular protein synthesis, lipid transport and energy metabolism were the differentially regulated processes occurring during low salinity stress. These results will provide a resource for subsequent gene expression studies regarding environmental stress and a valuable gene information for a better understanding of immune mechanisms of L. vannamei under low salinity stress.

The crab Carcinus maenas as a suitable experimental model in ecotoxicology

Aquatic ecotoxicology broadly focuses on how aquatic organisms interact with pollutants in their environment in order to determine environmental hazard and potential risks to humans. Research has produced increasing evidence on the pivotal role of aquatic invertebrates in the assessment of the impact of pollutants on the environment. Its potential use to replace fish bioassays, which offers ethical advantages, has already been widely studied. Nevertheless, the selection of adequate invertebrate experimental models, appropriate experimental designs and bioassays, as well as the control of potential confounding factors in toxicity testing are of major importance to obtain scientifically valid results. Therefore, the present study reviews more than four decades of published research papers in which the Green crab Carcinus maenas was used as an experimental test organism. In general, the surveyed literature indicates that C. maenas is sensitive to a wide range of aquatic pollutants and that its biological responses are linked to exposure concentrations or doses. Current scientific knowledge regarding the biology and ecology of C. maenas and the extensive studies on toxicology found for the present review recognise the Green crab as a reliable estuarine/marine model for routine testing in ecotoxicology research and environmental quality assessment, especially in what concerns the application of the biomarker approach. Data gathered provide valuable information for the selection of adequate and trustworthy bioassays to be used in C. maenas toxicity testing. Since the final expression of high quality testing is a reliable outcome, the present review recommends gender, size and morphotype separation in C. maenas experimental designs and data evaluation. Moreover, the organisms' nutritional status should be taken into account, especially in long-term studies. Studies should also consider the crabs' resilience when facing historical and concurrent contamination. Finally, experimental temperature and salinity should be harmonised so as to obtain reliable comparisons between different studies. Concerning future reaserch areas, data gathered in the present review reveals that in vitro assays derived from C. maenas are still lacking. Also, a complete C. maenas genome sequencing programme will be essencial for cutting-edge reseach.

The arginine kinase in Zhikong scallop Chlamys farreri is involved in immunomodulation

Arginine kinase (AK) catalyzes the reversible phosphorylation of l-arginine to form phosphoarginine, and plays a critical role in energy metabolism in invertebrates. In the present study, a scallop AK gene was identified from Chlamys farreri with an open reading frame (ORF) of 1101bp encoding for a protein of 366 amino acids (designed as CfAK). An ATP-gua PtransN domain which was described as a guanidine substrate specificity domain (GS domain) and an ATP-gua Ptrans domian which was responsible for binding ATP, were both identified in CfAK. The mRNA transcripts of CfAK were detectable in haemocytes, hepatopancreas, adductor muscle, mantle, gill, kidney and gonad, with the highest expression level in the muscle and the lowest level in the hemocytes. The expression level of CfAK mRNA increased from fertilized eggs to eyebot, and reached the highest in the trochophore stage. The relative expression level of CfAK mRNA in muscle was up-regulated significantly after LPS (0.5mg/mL) stimulation, and reached the peak at 6h (5.2-fold, P<0.05). The activity of inducible nitric oxide synthase (iNOS) in the supernatant of muscle homogenate increased significantly from 3.2U/mg at 0 h to 9.7 U/mg at 12h after LPS stimulation, while the concentration of nitric oxide (NO) in the supernatant of muscle homogenate began to increase at 3h (21.55 μmol/L), and reached the top concentration at 24h (42.27 μmol/L), then recovered to the normal level after 48 h. The recombinant protein of CfAK (rCfAK) expressed in Escherichia coli displayed Arginine kinase activity, and its apparent K(m) was 0.82 ± 0.11 and 1.24 ± 0.13 mM for L-arginine and ATP-Na, respectively. The results indicated that the CfAK was involved in energy production and utilization during the whole life process, and might refer to the immunomodulation process via altering the NO concentration and iNOS activity in scallop Chlamys farreri.

Simultaneous determination of two major snow crab aeroallergens in processing plants by use of isotopic dilution tandem mass spectrometry

Snow crab is a major fishery in the North Atlantic region. During crab processing the proteins are aerosolized and some are responsible for development of occupational asthma. Tropomyosin and arginine kinase have recently been reported as major snow crab allergens. A liquid chromatographic tandem mass spectrometric method has been developed for simultaneous analysis of these two proteins in air samples collected from processing plants. These proteins were initially isolated then characterized by use of mass spectrometry to determine their primary structure and signature peptides. The signature peptides were chemically synthesized in light and heavy forms and used as standards for developing the multiple-reaction monitoring transitions to monitor allergen levels. A validation study was performed; precision and accuracy were 1.8-8% and 91-104%, respectively. Replicate air samples were collected on air filters from two crab-processing plants in Newfoundland and Labrador (NL) and four located in Quebec. In NL, measured levels of both tropomyosin and arginine kinase were between 1 and 20 ng m(-3). In Quebec plants, however, levels were found to be much higher at 2-2400 ng m(-3). Significant differences were also observed among the plants and individual processing workstations. For the first time arginine kinase has been detected in its aerosolized form in processing plants. In general, levels of the allergens were highest in the butchering and cooking areas; plant design can, however, have a significant effect on levels of the allergens.

Cloning and expression of arginine kinase from a swimming crab, Portunus trituberculatus

Arginine kinase (AK) is an important phosphotransferase that plays a critical role in energy metabolism in invertebrates. In this paper, the cDNA of AK (designated as PtAK) was identified from the eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA was 1,479 bp, containing an open reading frame of 1,074 bp that coded for 357 amino acids. The estimated molecular mass of mature PtAK was 40.30 kDa and theoretical isoelectric point was 6.18. Amino acid sequence alignment showed that PtAK had very high similarity with other shrimp and crab AKs ranging from 0.876 to 0.983. The genomic DNA fragments of about 1,434 bp consisted of two exons interrupted by an intron. Totally 24 SNPs, including 17 in the coding region and seven in the non-coding region, were detected by direct sequencing of 19 genomic samples. In exon 1, the coding SNPs (cSNPs) were only found in the disease-resistant specimens. The fluorescent real-time PCR analysis revealed that the expression of PtAK was detected in all the examined tissues with the highest expression in the muscle and the lowest in the eyestalk. The expression of PtAK after Vibrio alginolyticus injection was tested in haemocytes, showing that two peak values were 5.01-fold (at 3 h) and 3.60-fold (at 24 h) compared with the control values, respectively. The results suggested that AK might play an important role in the immune response in crabs.

Effects of elevated seawater pCO(2) on gene expression patterns in the gills of the green crab, Carcinus maenas

Background

The green crab Carcinus maenas is known for its high acclimation potential to varying environmental abiotic conditions. A high ability for ion and acid-base regulation is mainly based on an efficient regulation apparatus located in gill epithelia. However, at present it is neither known which ion transport proteins play a key role in the acid-base compensation response nor how gill epithelia respond to elevated seawater pCO₂ as predicted for the future. In order to promote our understanding of the responses of green crab acid-base regulatory epithelia to high pCO₂, Baltic Sea green crabs were exposed to a pCO₂ of 400 Pa. Gills were screened for differentially expressed gene transcripts using a 4,462-feature microarray and quantitative real-time PCR.

Results

Crabs responded mainly through fine scale adjustment of gene expression to elevated pCO₂. However, 2% of all investigated transcripts were significantly regulated 1.3 to 2.2-fold upon one-week exposure to CO₂ stress. Most of the genes known to code for proteins involved in osmo- and acid-base regulation, as well as cellular stress response, were were not impacted by elevated pCO₂. However, after one week of exposure, significant changes were detected in a calcium-activated chloride channel, a hyperpolarization activated nucleotide-gated potassium channel, a tetraspanin, and an integrin. Furthermore, a putative syntaxin-binding protein, a protein of the transmembrane 9 superfamily, and a Cl^-/HCO₃^- exchanger of the SLC 4 family were differentially regulated. These genes were also affected in a previously published hypoosmotic acclimation response study.

Conclusions

The moderate, but specific response of C. maenas gill gene expression indicates that (1) seawater acidification does not act as a strong stressor on the cellular level in gill epithelia; (2) the response to hypercapnia is to some degree comparable to a hypoosmotic acclimation response; (3) the specialization of each of the posterior gill arches might go beyond what has been demonstrated up to date; and (4) a re-configuration of gill epithelia might occur in response to hypercapnia.

Moult cycle specific differential gene expression profiling of the crab Portunus pelagicus

Background

Crustacean moulting is a complex process involving many regulatory pathways. A holistic approach to examine differential gene expression profiles of transcripts relevant to the moulting process, across all moult cycle stages, was used in this study. Custom cDNA microarrays were constructed for Portunus pelagicus. The printed arrays contained 5000 transcripts derived from both the whole organism, and from individual organs such as the brain, eyestalk, mandibular organ and Y-organ from all moult cycle stages.

Results

A total of 556 clones were sequenced from the cDNA libraries used to construct the arrays. These cDNAs represented 175 singletons and 62 contigs, resulting in 237 unique putative genes. The gene sequences were classified into the following biological functions: cuticular proteins associated with arthropod exoskeletons, farnesoic acid O-methyltransferase (FaMeT), proteins belonging to the hemocyanin gene family, lectins, proteins relevant to lipid metabolism, mitochondrial proteins, muscle related proteins, phenoloxidase activators and ribosomal proteins. Moult cycle-related differential expression patterns were observed for many transcripts. Of particular interest were those relating to the formation and hardening of the exoskeleton, and genes associated with cell respiration and energy metabolism.

Conclusions

The expression data presented here provide a chronological depiction of the molecular events associated with the biological changes that occur during the crustacean moult cycle. Tracing the temporal expression patterns of a large variety of transcripts involved in the moult cycle of P. pelagicus can provide a greater understanding of gene function, interaction, and regulation of both known and new genes with respect to the moulting process.

The encysted dormant embryo proteome of Artemia sinica

The possibility of the brine shrimp Artemia to produce dormant embryo (cysts) in diapause is a key feature in its life history. In the present study, we obtained a proteomic reference map for the diapause embryo of Artemia sinica using two-dimensional gel electrophoresis with a pH range of 4-7 and a molecular weight range of 10-100 kDa. Approximately 233 proteins were detected, and 60 of them were analyzed by capillary liquid chromatography tandem mass spectrometry (LC-MS/MS). Of these, 39 spots representing 33 unique proteins were identified, which are categorized into functional groups, including cell defense, cell structure, metabolism, protein synthesis, proteolysis, and other processes. This reference map will contribute toward understanding the state of the diapause embryo and lay the basis and serve as a useful tool for further profound studies in the proteomics of Artemia at different developmental stages and physiological conditions.

Differential expression and induction of two carbonic anhydrase isoforms in the gills of the euryhaline green crab, Carcinus maenas, in response to low salinity

Two isoforms of the enzyme carbonic anhydrase (CA) from the gills of the euryhaline green crab were sequenced and identified; these were found to match the cytoplasmic (CAc) and membrane-associated (CAg) isoforms known from other species. The mRNA of the membrane-associated isoform is present in significantly higher levels of abundance in gills of crabs acclimated to 32 ppt, at which the crab is an osmotic and ionic conformer. Upon transfer to low salinity (15 ppt), in which the crab is an osmoregulator, however, the cytoplasmic isoform undergoes a rapid 100-fold increase in abundance in the posterior gills, becoming the dominant isoform. CAg increases 3-fold initially and then remains elevated through 14 days of low salinity acclimation. The induction of CAc mRNA is believed to be the molecular basis for the 20 fold increase in CA protein-specific activity during low salinity acclimation. The initial increase in CAc mRNA takes place at 6 h, and maximal levels of expression are achieved by 24 h; this precedes the induction of CA activity and is within the time in which hemolymph osmotic and ionic concentrations stabilize at new acclimated levels. The increase in expression of the CAg isoform is believed to be more closely related to changes in the population of branchial chloride cells. Changes in the relative abundance of mRNA for the alpha-subunit of the Na(+)/K(+)-ATPase were smaller in magnitude than those for CAc, but the timing was similar. There were no changes in expression of a control gene, arginine kinase (AK) in posterior gills, and there were no significant changes in expression in anterior gills for any of the genes measured here. These results support the use of a control tissue (anterior gills) in addition to a control gene for expression studies.

Gill-specific transcriptional regulation of Na+/K+ -ATPase alpha-subunit in the euryhaline shore crab Pachygrapsus marmoratus: sequence variants and promoter structure

The sodium pump (Na+/K+ -ATPase) has been implicated in osmoregulatory ion transport in many aquatic animals. In the euryhaline hyper-hypoosmoregulating shore crab Pachygrapsus marmoratus, induction of Na+/K+ -ATPase alpha-subunit mRNA varies between gills in response to osmotic stress. Following transfer of crabs from normal seawater (36 per thousand salinity) to diluted seawater (10 per thousand), a condition in which gills exhibit net ion uptake, alpha-subunit mRNA expression is upregulated in all tested gills, albeit with differing time courses. By contrast, following transfer from seawater to hypertonic (45 per thousand) seawater, a condition in which the animal is excreting ions, alpha-subunit mRNA is induced primarily in gill no. 7 (nine in total), suggesting that this gill may be associated specifically with ion excretion in P. marmoratus. Full-length sequencing of alpha-subunit cDNA revealed the existence of two isoforms differing only in the inclusion of an 81-nucleotide segment within the N-terminal open reading frame of the long (D) form in comparison to the short (C) form. The 81-nucleotide segment encodes a 14-3-3 protein binding site that may facilitate movement of the alpha-subunit protein between intracellular compartments and the plasma membrane. mRNA expression of the two forms followed similar patterns upon salinity transfer. Genomic DNA sequencing of the putative promoter region of the alpha-subunit gene demonstrated a spectrum of predicted transcription factor binding sites that are likely associated with the complex expression pattern observed among gills following osmotic stress.

Cloning, expression, purification, and characterization of arginine kinase from Locusta migratoria manilensis

Arginine kinase (AK) is a phosphotransferase that plays a critical role in energy metabolism in invertebrates. The gene encoding Locusta migratoria manilensis AK was cloned and expressed in Escherichia coli by two prokaryotic expression plasmids, pET-30a and pET-28a. The recombinant protein was expressed as inclusion bodies using pET-30a. After denaturation, the recombinant AK was successfully renatured and confirmed to be enzymatically active. Addition of Tween-20 and SDS to the dilution system led to higher renaturation efficiency. Using another expression plasmid, pET-28a, and changing the expression conditions resulted in a soluble and functional form of AK, which was purified by an improved method using Sephadex G-75 chromotography to a final yield of 358 mg L(-1) of LB medium. Some parameters for the renatured and soluble forms of AK, including Km, Kd, specific activity, electrophoretic mobility and isoelectric focusing, were identical with those of AK obtained directly from L. migratoria manilensis leg muscle. Comparison of kinetic constants with those of AKs from other sources indicated that L. migratoria manilensis AKs have the highest kcat and stronger synergistic substrate binding. The first report of a concise purification method enables the enzyme to be prepared in large quantities. This research should enable further detailed investigations of the enzymatic mechanism by site directed mutagenesis techniques.

Salinity-stimulated changes in expression and activity of two carbonic anhydrase isoforms in the blue crabCallinectes sapidus

Two isoforms of the enzyme carbonic anhydrase (CA) in the blue crab gill,CasCAg and CasCAc, were identified, sequenced, and found to match the membrane-associated and cytoplasmic isoforms, respectively. The membrane-associated isoform is present in much higher levels of mRNA expression in both anterior and posterior gills in crabs acclimated to high salinity (35 p.p.t.), but expression of the cytoplasmic isoform in the posterior gill undergoes a significantly greater degree of up-regulation after exposure to low salinity (15 p.p.t.). CasCAc has the largest scope of induction (100-fold) reported for any transport-related protein in the gill,and this may be necessary to overcome diffusion limitations between gill cytoplasm and the apical boundary layer. Furthermore, the timing of the changes in expression of CasCAc corresponds to the timing of the induction of protein-specific CA activity and CA protein concentration. No changes in CA mRNA expression or activity occur in the anterior gills. The pattern of up-regulation of expression of mRNA of the α-subunit of the Na+/K+-ATPase is similar to that for CasCAc, and both precede the establishment of the new acclimated physiological state of the crab in low salinity. A putative `housekeeping' gene, arginine kinase, also showed about a threefold increase in expression in response to low salinity,but only in the posterior gills. These results suggest that for studies of expression in crustacean gill tissue, a control tissue, such as the anterior gill, be used until an adequate control gene is identified.

Quantitative changes in branchial carbonic anhydrase activity and expression in the euryhaline green crab,Carcinus maenas, in response to low salinity exposure

Hemolymph osmolality, and changes in gill carbonic anhydrase (CA) activity, relative mRNA expression, and CA protein concentration were measured in the green crab Carcinus maenas acclimated to 32 ppt salinity and transferred to 10 ppt. Hemolymph osomolality stabilized at new, acclimated values, by 24 hr after transfer. There was a large increase in CA mRNA concentrations, as measured by quantitative PCR, in the posterior gills by 24 hr post-transfer that remained elevated through 4 days. By 7 days, however, CA mRNA levels began to decline. CA activity, on the other hand, did not begin to increase until 48 hr after transfer to 10 ppt, but it continued to increase through 7 days. CA protein concentration increased by 5-fold in posterior gills in crabs acclimated to 10 ppt. CA activity, mRNA expression, and CA protein concentrations did not change in anterior gills. These results indicate that low salinity-stimulated CA induction is under transcriptional regulation, and that the increase in CA activity is a result of the increase in gene expression and synthesis of new enzyme. Changes in mRNA appear to be transient, but once synthesized, the CA protein appears to persist in the gill for an extended time. In a separate set of experiments, green crabs acclimated to 32 ppt were transferred directly to salinities of 25, 20, 15, and 10 ppt. CA activity and mRNA concentrations increased with decreasing salinity, peaking at 15 ppt but decreasing between 15 and 10 ppt. The decrease may represent a breakdown in the mechanism of transport-related protein induction near the lower salinity limit of this species.

Expression profiles of Na+,K+-ATPase during acute and chronic hypo-osmotic stress in the blue crab Callinectes sapidus

During acclimation to dilute seawater, the specific activity of Na+,K+-ATPase increases substantially in the posterior gills of the blue crab Callinectes sapidus. To determine whether this increase occurs through regulation of pre-existing enzyme or synthesis of new enzyme, mRNA and protein levels were measured over short (<24 h) and long (18 days) time courses. Na+,K+-ATPase expression, both mRNA and protein, did not change during the initial 24-h exposure to dilute seawater (10 ppt salinity). Thus, osmoregulation in C. sapidus during acute exposure to low salinity likely involves either modulation of existing enzyme or mechanisms other than an increase in the amount of Na+,K+-ATPase enzyme. However, crabs exposed to dilute seawater over 18 days showed a 300% increase in Na+,K+-ATPase specific activity as well as a 200% increase in Na+,K+-ATPase protein levels. Thus, it appears that the increase in Na+,K+-ATPase activity during chronic exposure results from the synthesis of new enzyme. The relative amounts of mRNA for the alpha-subunit increased substantially (by 150%) during the acclimation process, but once the crabs had fully acclimated to low salinity, the mRNA levels had decreased and were not different from levels in crabs fully acclimated to high salinity. Thus, there is transient induction of the Na+,K+-ATPase mRNA levels during acclimation to dilute seawater.

Functional evidence for the presence of a carbonic anhydrase repressor in the eyestalk of the euryhaline green crabCarcinus maenas

Carbonic anhydrase (CA) activity and relative expression of CA mRNA were measured in the gills of the euryhaline green crab Carcinus maenas in response to eyestalk ablation (ESA), injection of eyestalk extract and exposure to low salinity. For crabs acclimated to 32 p.p.t. salinity, ESA alone resulted in an increase in both CA activity and relative mRNA expression in the posterior, ion-transporting gills, but not in the anterior, respiratory gills. The ESA-stimulated increase in CA activity was abolished by injections of extracts of eyestalks taken from crabs acclimated to 32 p.p.t. salinity. Transfer of intact crabs from 32 to 10 p.p.t. salinity for 7 days resulted in an eightfold increase in CA activity and a sixfold increase in mRNA expression in posterior gills. ESA potentiated the normal low salinity-mediated CA induction by 23%. Daily injections of eyestalk extract reduced low salinity-stimulated CA induction by nearly 50% in intact crabs and by almost 75% in eyestalk ablated crabs. A 4-day transfer to 10 p.p.t. salinity also caused significant increases in both CA activity and mRNA expression in posterior gills, and ESA resulted in a 32% increase in the normal degree of CA induction. Daily injections of eyestalk extracts reduced CA induction in a dose-dependent manner over the 4-day time course. When CA induction was reduced by 66%, hemolymph osmotic regulation was also disrupted. These results are functional evidence for the presence of a CA repressor in the major endocrine complex of the crab, the eyestalk. This compound appears to function in keeping CA expression at low, baseline levels in crabs at high salinity. Exposure to low salinity removes the effects of the putative repressor,allowing CA expression, and thus CA activity, to increase.

Induction of branchial ion transporter mRNA expression during acclimation to salinity change in the euryhaline crab Chasmagnathus granulatus

Using quantitative real-time PCR, the expression of mRNAs encoding three transport-related proteins and one putative housekeeping protein was analyzed in anterior and posterior gills of the euryhaline crab Chasmagnathus granulatus following transfer from isosmotic conditions (30 per thousand salinity) to either dilute (2 per thousand) or concentrated (45 per thousand) seawater. Modest changes were observed in the abundance of mRNAs encoding the housekeeping protein arginine kinase and the vacuolar-type H(+)-ATPase B-subunit, both of which were highly expressed under all conditions. By contrast, the expression of Na(+)/K(+)-ATPase alpha-subunit mRNA and Na(+)/K(+)/2Cl(-) cotransporter mRNA was strongly responsive to external salinity. During acclimation to dilute seawater, cotransporter mRNA increased 10-20-fold in posterior gills within the first 24 h while Na(+)/K(+)-ATPase alpha-subunit mRNA increased 35-55-fold. During acclimation to concentrated seawater, cotransporter mRNA increased 60-fold by 96 h and Na(+)/K(+)-ATPase alpha-subunit increased approximately 25-fold in posterior gills. Our results indicate a complex pattern of transcriptional regulation dependent upon the direction of salinity change and the developmental background of the gills.

Gill area, permeability and Na+,K+-ATPase activity as a function of size and salinity in the blue crab,Callinectes sapidus

Juvenile blue crabs, Callinectes sapidus, extensively utilize oligohaline and freshwater regions of the estuary. With a presumptively larger surface-area-to-body weight ratio, juvenile crabs could experience osmo- and ionoregulatory costs well in excess of that of adults. To test this hypothesis, crabs ranging over three orders of magnitude in body weight were acclimated to either sea water (1,000 mOsm) or dilute sea water (150 mOsm), and gill surface area, water and sodium permeabilities (calculated from the passive efflux of 3H2O and 22Na+), gill Na+, K+ -ATPase activity and expression were measured. Juveniles had a relatively larger gill surface area; weight-specific gill surface area decreased with body weight. Weight-specific water and sodium fluxes also decreased with weight, but not to the same extent as gill surface area; thus juveniles were able to decrease gill permeability slightly more than adults upon acclimation to dilute media. Crabs < 5 g in body weight had markedly higher activities of gill Na+ ,K+ -ATPase than crabs > 5 g in both posterior and anterior gills. Acclimation to dilute medium induced increased expression of Na+, K+ -ATPase and enzyme activity, but the increase was not as great in juveniles as in larger crabs. The increased weight-specific surface area for water gain and salt loss for small crabs in dilute media presents a challenge that is incompletely compensated by reduced permeability and increased affinity of gill Na+, K+ -ATPase for Na+. Juveniles maintain osmotic and ionic homeostasis by the expression and utilization of extremely high levels of gill Na+, K+ -ATPase, in posterior, as well as in anterior, gills.

Proteome analysis of abundantly expressed proteins from unfed larvae of the cattle tick, Boophilus microplus

Protein expression in unfed larvae of the cattle tick, Boophilus microplus, was characterized using gel electrophoresis and mass spectrometry in an effort to assemble a database of proteins produced at this stage of development. Soluble and insoluble proteins were extracted and resolved by two-dimensional (2D) gel electrophoresis. Twenty abundantly expressed larval proteins were selected for peptide mass mapping and for peptide sequencing by matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) and quadrupole time-of-flight (Q-ToF) tandem mass spectrometry (MS), respectively. Only one protein, tropomyosin, was unequivocally identified from its peptide mass map. Ten proteins were assigned putative identities based on BLAST searching of heterologous databases with peptide sequences. These included a cytoskeletal protein (troponin I), multiple cuticular proteins, a glycine-rich salivary gland-associated protein and proteins with a presumed housekeeping role (arginine kinase, a high-mobility group protein and a small heat shock protein). Eight additional proteins were identified by searching translated open reading frames of a B. microplus EST database (unpublished): putative fatty-acid binding protein, thioredoxin, glycine-rich salivary gland protein and additional cuticular proteins. One remaining protein was not identifiable, suggesting it may be a novel molecule. The ongoing assembly of this database contributes to our understanding of proteins expressed by the tick and provides a resource that can be mined for molecules that play a role in tick-host interactions.

Salinity-mediated carbonic anhydrase induction in the gills of the euryhaline green crab, Carcinus maenas

The euryhaline green crab, Carcinus maenas, is a relatively strong osmotic and ionic regulator, being able to maintain its hemolymph osmolality as much as 300 mOsm higher than that in the medium when the crab is acclimated to low salinity. It makes the transition from osmoconformity to osmoregulation at a critical salinity of 26 ppt, and new acclimated concentrations of hemolymph osmotic and ionic constituents are reached within 12 h after transfer to low salinity. One of the central features of this transition is an 8-fold induction of the enzyme carbonic anhydrase (CA) in the gills. This induction occurs primarily in the cytoplasmic pool of CA in the posterior, ion-transporting gills, although the membrane-associated fraction of CA also shows some induction in response to low salinity. Inhibition of branchial CA activity with acetazolamide (Az) has no effect in crabs acclimated to 32 ppt but causes a depression in hemolymph osmotic and ionic concentrations in crabs acclimated to 10 ppt. The salinity-sensitive nature of the cytoplasmic CA pool and the sensitivity of hemolymph osmotic/ionic regulation to Az confirm the enzyme's role in ion transport and regulation in this species. CA induction is a result of gene activation, as evidenced by an increase in CA mRNA at 24 h after transfer to low salinity and an increase in protein-specific CA activity immediately following at 48 h post-transfer. CA gene expression appears to be under inhibitory control by an as-yet unidentified repressor substance found in the major endocrine complex of the crab, the eyestalk.

Moult cycle-related changes in biological activity of moult-inhibiting hormone (MIH) and crustacean hyperglycaemic hormone (CHH) in the crab, Carcinus maenas. From target to transcript

The currently accepted model of moult control in crustaceans relies entirely on the hypothesis that moult-inhibiting hormone (MIH) and crustacean hyperglycaemic hormone (CHH) repress ecdysteroid synthesis of the target tissue (Y-organ) only during intermoult, and that changes in synthesis and/or release of these neurohormones are central to moult control. To further refine this model, we investigated the biological activities of these neuropeptides in the crab Carcinus maenas, at the target tissue, receptor and cellular level by bioassay (inhibition of ecdysteroid synthesis), radioligand (receptor) binding assays, and second messenger (cGMP) assays, at defined stages of the moult cycle. To investigate possible moult cycle-related changes in neuropeptide biosynthesis, steady-state transcript levels of both neuropeptide mRNAs were measured by quantitative RT-PCR, and stored neuropeptide levels in the sinus gland were quantified during intermoult and premoult. The results show that the most important level of moult control lies within the signalling machinery of the target tissue, that expression and biosynthesis of both neuropeptides is constant during the moult cycle, and are not central to the currently accepted model of moult control.

Scaling of gill metabolic potential as a function of salinity in the euryhaline crab, Callinectes sapidus rathbun

The body-size scaling pattern of enzymes that are important in energy metabolism was examined in gills of the blue crab as a function of acclimation salinity. We hypothesized that the higher surface-area-to-volume ratio of small crabs would impose a greater metabolic cost for hyperosmoregulation, leading to an increase in the capacity for ATP production in gills. Postmetamorphic crabs spanning a 2,500-fold range in body mass were examined following a 7-d exposure to a salinity of 35, 17, or 5 ppt. The posterior gills, which are the principal site of osmoregulatory ion pumping, generally had higher activities than the anterior gills, which are primarily used for gas exchange, and this discrepancy was greatest in small crabs. A significant effect of salinity was found only for the enzyme citrate synthase, where the activity was highest at the lowest salinity. Although most enzymes scaled negatively with body mass, the activity was independent of size over a 250-fold size range that encompassed the body masses of juvenile crabs but decreased abruptly in the adult crabs. These data suggest that ion pumping associated with osmoregulation may represent a greater energetic challenge in smaller crabs, and this is reflected in the relatively higher metabolic potential of the posterior gills. However, acclimation to different salinity regimes does not lead to dramatic global changes in the capacity for energy metabolism.

Na++K+-ATPase in gills of the blue crabCallinectes sapidus: cDNA sequencing and salinity-related expression of α-subunit mRNA and protein

Many studies have shown that hyperosmoregulation in euryhaline crabs is accompanied by enhanced Na++K+-ATPase activity in the posterior gills, but it remains unclear whether the response is due to regulation of pre-existing enzyme or to increased gene transcription and mRNA translation. To address this question, the complete open reading frame and 3′ and 5′ untranslated regions of the mRNA coding for the α-subunit of Na++K+-ATPase from the blue crab Callinectes sapidus were amplified by reverse transcriptase/polymerase chain reaction (RT-PCR) and sequenced. The resulting 3828-nucleotide cDNA encodes a putative 1039-amino-acid protein with a predicted molecular mass of 115.6 kDa. Hydrophobicity analysis of the amino acid sequence indicated eight membrane-spanning regions, in agreement with previously suggested topologies. The α-subunit amino acid sequence is highly conserved among species, with the blue crab sequence showing 81–83 % identity to those of other arthropods and 74–77 % identity to those of vertebrate species. Quantitative RT-PCR analysis showed high levels of α-subunit mRNA in posterior gills 6–8 compared with anterior gills 3–5. Western blots of gill plasma membranes revealed a single Na++K+-ATPase α-subunit protein band of the expected size. The posterior gills contained a much higher level of α-subunit protein than the anterior gills, in agreement with previous measurements of enzyme activity. Immunocytochemical analysis showed that the Na++K+-ATPase α-subunit protein detected by α5 antibody is localized to the basolateral membrane region of gill epithelial cells. Transfer of blue crabs from 35 to 5 ‰ salinity was not accompanied by notable differences in the relative proportions of α-subunit mRNA and protein in the posterior gills, suggesting that the enhanced Na++K+-ATPase enzyme activity that accompanies the hyperosmoregulatory response may result from post-translational regulatory processes.

Molecular characterization of V-type H(+)-ATPase (B-subunit) in gills of euryhaline crabs and its physiological role in osmoregulatory ion uptake

The vacuolar-type H(+)-ATPase (V-ATPase) has been implicated in osmoregulatory ion uptake across external epithelia of a growing variety of species adapted to life in fresh water. In the present study, we investigated whether the V-ATPase may also function in a euryhaline species that tolerates brackish water (8 salinity) but not fresh water, the shore crab Carcinus maenas. cDNA coding for the regulatory B-subunit of the V-ATPase was amplified and sequenced from C. maenas gills and partially sequenced from four other crab species. Two isoforms differing in the 3′-untranslated region were found in C. maenas. In this species, the abundance of B-subunit mRNA was greater in the respiratory anterior gills than the ion-transporting posterior gills and was not increased by acclimation to dilute salinity. Immunocytochemical analysis showed that the B-subunit protein is not targeted to the apical membrane but is distributed throughout the cytoplasmic compartment. Physiological studies of isolated perfused gills indicated that the V-ATPase inhibitor bafilomycin had no effect on transepithelial potential difference. Thus, in contrast to the freshwater-tolerant Chinese crab Eriocheir sinensis, in which the V-ATPase appears to play an important osmoregulatory role, the V-ATPase in C. maenas probably functions in acidification of intracellular organelles but not in transbranchial NaCl uptake.