The effects of bisphenol S exposure on the growth, physiological and biochemical indices, and ecdysteroid receptor gene expression in red swamp crayfish, Procambarus clarkii

The experiment was conducted to investigate the effects of Bisphenol S (BPS) on growth, physiological and biochemical indices, and the expression of ecdysteroid receptor (ECR) of the red swamp crayfish (Procambarus clarkii). The gene encoding ECR was isolated from red swamp crayfish by homologous cloning and rapid amplification of cDNA ends (RACE). The ECR transcripts were 1757 bp long and encoded proteins of 576 amino acids. The quantitative real-time PCR (qRT-PCR) analysis showed that the ECR gene was expressed in various tissues under normal conditions, and the highest level was observed in the ovary and the lowest level was observed in the muscle (P < 0.05). Then, the experiment was designed with four different BPS concentrations (0, 1, 10, and 100 μg/L), BPS exposure for 14 days, three parallel groups, and a total of 240 red swamp crayfish. At 100 μg/L BPS, the survival rate, weight gain rate, and relative length rate were decreased significantly (P < 0.05). Malonaldehyde (MDA) content reached the highest level at 100 μg/L BPS. When BPS concentration was higher than 10 μg/L, the activities of superoxide dismutase (SOD) and catalase (CAT) were significantly lower than those of the control group (P < 0.05). The expression levels of the ECR gene in ovary, intestinal, gill, and hepatopancreas tissues were significantly increased after BPS exposure (P < 0.05). The ECR gene expression in ovaries and Y-organs was significantly higher than other groups in 10 μg/L BPS (P < 0.05). The expressions of the tumor necrosis factor -α (TNF-α) and interleukin-6 (IL-6) genes in the hepatopancreas gradually increased, and the highest expression was observed exposed in 100 μg/L BPS (P < 0.05). This research will provide novel insights into the health risk assessment of BPS in aquatic organisms.

An ecdysteroid-regulated 16-kDa protein homolog participates in the immune response of the crayfish Procambarus clarkii

An ecdysteroid-regulated 16-kDa protein homolog (named Pc-E16), encoding 150 amino acid residues with a conserved MD-2-related lipid-recognition domain, was first identified in Procambarus clarkii. Phylogenetic analyses indicated similarity between Pc-E16 and 16-kDa proteins from Aplysia californica and insects. Recombinant Pc-E16 protein was successfully expressed in BL21 (DE3) Escherichia coli cells, and polyclonal antibodies against purified Pc-E16 proteins were prepared. In comparison with other tissues, Pc-E16 was highly expressed in the intestine; real-time PCR and Western blotting results indicated that Pc-E16 expression was significantly induced by lipopolysaccharides in hepatopancreas and hemocytes. Pc-E16-mediated signaling pathways were investigated by digital gene expression analysis following RNA interference targeting Pc-E16. A total of 6103 differentially expressed genes (DEGs) were identified, of which 3318 were up- and 2785 were downregulated. Many DEGs were involved in binding and catalytic activity. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that DEGs were clustered into 225 pathways, and 15 significantly enriched pathways were identified at the immune system level. In addition, the expression level of Pc-E16 in hemocytes and hepatopancreas was obviously downregulated at 48 h after dsRNA injection, and Pc-E16-RNAi treatment affected the expression levels of immune-related genes. Altogether, our results suggest that Pc-E16 is involved in the innate immune response of P. clarkii.

Ammonia Stress Disturbs Moult Signaling in Juvenile Swimming Crab Portunus trituberculatus

Ammonia is a significant concern during hatchery culture in brachyuran species, and its accumulation may lead to abortive moulting and large-scale deaths of the early juveniles. To date, the underlying mechanism for ammonia-induced alteration of the moulting process is still unknown. In this study, we aimed to investigate the effects of ammonia on the moulting as well as the potential mechanisms in early juveniles of the swimming crab Portunus trituberculatus, an important aquaculture species in China. We evaluated the survival rate and moulting rate of the juvenile crabs (C2) and analyzed the expression pattern of the genes in key components of molt signaling during a complete moulting cycle under different concentrations of ammonia nitrogen (the control group: <0.1 mg/L; the LA group: 5 mg/L; and the HA group: 20 mg/L). The results showed that: (1) the survival rate in the LA and HA groups was lower than that in the control group at the end of the experiment, and moulting death syndrome (MDS) was only observed in the HA group; (2) the moulting rate was higher in the LA group and lower in the HA group compared to the control group; (3) consistent with the results of the moulting experiment, MIH showed decreased expression, and genes related to ecdysteroid synthesis, ecdysteroid receptors, and responsive effectors exhibited increased expression in the LA group compared to the control group; and (4) although MIH expression was upregulated, increased expression of the genes associated with ecdysteroid synthesis, ecdysteroid receptors and downstream effectors still observed in the HA group. Our results indicated that low levels of ammonia can promote moulting in juvenile swimming crabs by inhibiting the expression of MIH and activating moult signaling, whereas high levels of ammonia inhibit moulting and lead to MDS through impairing moult signaling.

CasEcR and CasMIH Genes in the Blue Crab, Callinectes sapidus: A Temporal Evaluation and Melatonin Effects

Environmental cues synchronize endogenous rhythms of many physiological processes such as hormone synthesis and secretion. Little is known about the diurnal pattern of hormones and gene expression of the Callinectes sapidus molt cycle. We aimed to investigate in the eyestalk and hepatopancreas of premolt and intermolt C. sapidus the following parameters: 1) the diurnal expression of the ecdysteroid receptor CasEcR isoforms, and the molt inhibiting hormone CasMIH; 2) the diurnal hemolymph ecdysteroid and melatonin levels; and 3) melatonin effects on the transcripts of the above-mentioned genes in intermolt C. sapidus. Ecdysteroid levels were higher in the premolt than the intermolt animals at all time points evaluated (ZTs). Premolt crabs displayed a variation of ecdysteroid concentration between time points, with a reduction at ZT17. No difference in the melatonin level was seen in either molt stage or between stages. In the eyestalk of intermolt animals, CasEcR expression oscillated, with a peak at ZT9, and premolt crabs have a reduction at ZT9; CasMIH transcripts did not vary along 24 h in either molt stage. Moreover, the evaluated eyestalk genes were more expressed at ZT9 in the intermolt than the premolt crabs. In the hepatopancreas, CasEcR expression showed a peak at ZT9 in premolt crabs. Exogenous melatonin (10⁻⁷ mol/animal) reduced the expression of both genes in the eyestalk at ZT17. In the hepatopancreas, melatonin markedly increased the expression of the CasEcR gene at ZT9. Taken altogether, our results are pioneer in demonstrating the daily oscillation of gene expression associated to molt cycle stages, as well as the daily ecdysteroid and melatonin levels and the remarkable influence of melatonin on the molt cycle of C. sapidus.

From sporadic single genes to a broader transcriptomic approach: Insights into the formation of the biomineralized exoskeleton in decapod crustaceans

One fundamental character common to pancrustaceans (Crustacea and Hexapoda) is a mineralized rigid exoskeleton whose principal organic components are chitin and proteins. In contrast to traditional research in the field that has been devoted to the structural and physicochemical aspects of biomineralization, the present study explores transcriptomic aspects of biomineralization as a first step towards adding a complementary molecular layer to this field. The rigidity of the exoskeleton in pancrustaceans dictates essential molt cycles enabling morphological changes and growth. Thus, formation and mineralization of the exoskeleton are concomitant to the timeline of the molt cycle. Skeletal proteinaceous toolkit elements have been discovered in previous studies using innovative molt-related binary gene expression patterns derived from transcriptomic libraries representing the major stages comprising the molt cycle of the decapod crustacean Cherax quadricarinatus. Here, we revisited some prominent exoskeleton-related structural proteins encoding and, using the above molt-related binary pattern methodology, enlarged the transcriptomic database of C. quadricarinatus. The latter was done by establishing a new transcriptomic library of the cuticle forming epithelium and molar tooth at four different molt stages (i.e., inter-molt, early pre-molt, late pre-molt and post-molt) and incorporating it to a previous transcriptome derived from the gastroliths and mandible. The wider multigenic approach facilitated by the newly expanded transcriptomic database not only revisited single genes of the molecular toolkit, but also provided both scattered and specific information that broaden the overview of proteins and gene clusters which are involved in the construction and biomineralization of the exoskeleton in decapod crustaceans.

CPAP3 proteins in the mineralized cuticle of a decapod crustacean

The pancrustacean theory groups crustaceans and hexapods (once thought to comprise separate clades within the Arthropoda) into a single clade. A key feature common to all pancrustaceans is their chitinous exoskeleton, with a major contribution by cuticular proteins. Among these, are the CPAP3’s, a family of cuticular proteins, first identified in the hexapod Drosophila melanogaster and characterized by an N-terminal signaling peptide and three chitin-binding domains. In this study, CPAP3 proteins were mined from a transcriptomic library of a decapod crustacean, the crayfish Cherax quadricarinatus. Phylogenetic analysis of other CPAP3 proteins from hexapods and other crustaceans showed a high degree of conservation. Characterization of the crayfish proteins, designated CqCPAP3’s, suggested a major role for CPAP3’sin cuticle formation. Loss-of-function experiments using RNAi supported such a notion by demonstrating crucial roles for several CqCPAP3 proteins during molting. A putative mode of action for the CqCPAP3 proteins –theoretically binding three chitin strands– was suggested by the structural data obtained from a representative recombinant CqCPAP3. The similarities between the CqCPAP3 proteins and their hexapod homologues further demonstrated common genetic and proteinaceous features of cuticle formation in pancrustaceans, thereby reinforcing the linkage between these two highly important phylogenetic groups.

Transcriptomic variation of eyestalk reveals the genes and biological processes associated with molting in Portunus trituberculatus

Background

Molting is an essential biological process throughout the life history of crustaceans, which is regulated by many neuropeptide hormones expressed in the eyestalk. To better understand the molting mechanism in Portunus trituberculatus, we used digital gene expression (DGE) to analyze single eyestalk samples during the molting cycle by high-throughput sequencing.

Results

We obtained 14,387,942, 12,631,508 and 13,060,062 clean sequence reads from inter-molt (InM), pre-molt (PrM) and post-molt (PoM) cDNA libraries, respectively. A total of 1,394 molt-related differentially expressed genes (DEGs) were identified. GO and KEGG enrichment analysis identified some important processes and pathways with key roles in molting regulation, such as chitin metabolism, peptidase inhibitor activity, and the ribosome. We first observed a pattern associated with the neuromodulator-related pathways during the molting cycle, which were up-regulated in PrM and down-regulated in PoM. Four categories of important molting-related transcripts were clustered and most of them had similar expression patterns, which suggests that there is a connection between these genes throughout the molt cycle.

Conclusion

Our work is the first molt-related investigation of P. trituberculatus focusing on the eyestalk at the whole transcriptome level. Together, our results, including DEGs, identification of molting-related biological processes and pathways, and observed expression patterns of important genes, provide a novel insight into the function of the eyestalk in molting regulation.

Cloning and Expression of Ecdysone Receptor and Retinoid X Receptor from Procambarus clarkii: Induction by Eyestalk Ablation

Ecdysone receptor and retinoid X receptor are key regulators in molting. Here, full length ecdysone receptor (PcEcR) and retinoid X receptor (PcRXR) cDNAs from Procambarus clarkii were cloned. Full length cDNA of PcEcR has 2500 bp, encoding 576 amino acid proteins, and full length cDNA of PcRXR has 2593 bp, in which a 15 bp and a 204 bp insert/deletion splice variant regions in DNA binding domain and hinge domain were identified. The two splice variant regions in PcRXR result four isoforms: PcRXR1-4, encoding 525, 520, 457 and 452 amino acids respectively. PcEcR was highly expressed in the hepatopancreas and eyestalk and PcRXR was highly expressed in the eyestalk among eight examined tissues. Both PcEcR and PcRXR had induced expression after eyestalk ablation (ESA) in the three examined tissues. In muscle, PcEcR and PcRXR were upregulated after ESA, PcEcR reached the highest level on day 3 after ESA and increased 33.5-fold relative to day 0, and PcRXR reached highest the level on day 1 after ESA and increased 2.7-fold relative to day 0. In the hepatopancreas, PcEcR and PcRXR dEcReased continuously after ESA, and the expression levels of PcEcR and PcRXR were only 0.7% and 1.7% on day 7 after ESA relative to day 0, respectively. In the ovaries, PcEcR was upregulated after ESA, reached the highest level on day 3 after ESA, increased 3.0-fold relative to day 0, and the expression level of PcRXR changed insignificantly after ESA (p > 0.05). The different responses of PcEcR and PcRXR after ESA indicates that different tissues play different roles (and coordinates their functions) in molting.

Genome-wide identification and transcript profile of the whole cathepsin superfamily in the intertidal copepod Tigriopus japonicus

Modulation of expression of cathepsins in innate immune response has previously been reported in mollusks and large crustaceans including crabs, lobsters, and shrimps in response to immune challenges. However, similar responses in copepods and the related cathepsin members remain under-investigated. To understand molecular and innate immune responses in the intertidal copepod Tigriopus japonicus, we identified the full spectra of cathepsin members (2 aspartyl proteases, 18 cysteine proteases, and 4 serine proteases) and also analyzed transcriptional expression of cathepsin (Tj-cathepsin) genes in developmental stages, lipopolysaccharide (LPS)- and two Vibrio species-exposed T. japonicus. The transcriptional levels of most Tj-cathepsin genes were highly increased during the molting transition from the nauplius to the copepodid stages. LPS treatment induced innate immune response via significant transcriptional increase of serine cathepsin (e.g., cathepsin As) members with induction of several cysteine cathepsin genes. However, Tj-aspartyl cathepsin E-like and a novel cysteine cathepsin were slightly reduced in response to LPS exposure. Interestingly, Vibrio species showed very low transcriptional sensitivity in the expression of entire cathepsins, while LPS induced several cathepsin gene-involved primitive immune responses in T. japonicus. In this paper, we discuss how whole cathepsin expression profiling can be linked to host defense mechanism to better understand and uncover the underlying mechanism of copepods' innate immunity.

A crayfish molar tooth protein with putative mineralized exoskeletal chitinous matrix properties

Some crustaceans possess exoskeletons that are reinforced with calcium carbonate. In the crayfish Cherax quadricarinatus, the molar tooth, which is part of the mandibular exoskeleton, contains an unusual crystalline enamel-like apatite layer. As this layer resembles vertebrate enamel in composition and function, it offers an interesting example of convergent evolution. Unlike other parts of the crayfish exoskeleton, which is periodically shed and regenerated during the molt cycle, molar mineral deposition takes place during the pre-molt stage. The molar mineral composition transforms continuously from fluorapatite through amorphous calcium phosphate to amorphous calcium carbonate and is mounted on chitin. The process of crayfish molar formation is entirely extracellular and presumably controlled by proteins, lipids, polysaccharides, low-molecular weight molecules and calcium salts. We have identified a novel molar protein termed Cq-M15 from C. quadricarinatus and cloned its transcript from the molar-forming epithelium. Its transcript and differential expression were confirmed by a next-generation sequencing library. The predicted acidic pI of Cq-M15 suggests its possible involvement in mineral arrangement. Cq-M15 is expressed in several exoskeletal tissues at pre-molt and its silencing is lethal. Like other arthropod cuticular proteins, Cq-M15 possesses a chitin-binding Rebers-Riddiford domain, with a recombinant version of the protein found to bind chitin. Cq-M15 was also found to interact with calcium ions in a concentration-dependent manner. This latter property might make Cq-M15 useful for bone and dental regenerative efforts. We suggest that, in the molar tooth, this protein might be involved in calcium phosphate and/or carbonate precipitation.

A novel chitin binding crayfish molar tooth protein with elasticity properties

The molar tooth of the crayfish Cherax quadricarinatus is part of the mandible, and is covered by a layer of apatite (calcium phosphate). This tooth sheds and is regenerated during each molting cycle together with the rest of the exoskeleton. We discovered that molar calcification occurs at the pre-molt stage, unlike calcification of the rest of the new exoskeleton. We further identified a novel molar protein from C. quadricarinatus and cloned its transcript from the molar-forming epithelium. We termed this protein Cq-M13. The temporal level of transcription of Cq-M13 in an NGS library of molar-forming epithelium at different molt stages coincides with the assembly and mineralization pattern of the molar tooth. The predicted protein was found to be related to the pro-resilin family of cuticular proteins. Functionally, in vivo silencing of the transcript caused molt cycle delay and a recombinant version of the protein was found to bind chitin and exhibited elastic properties.

Binary gene expression patterning of the molt cycle: the case of chitin metabolism

In crustaceans, like all arthropods, growth is accompanied by a molting cycle. This cycle comprises major physiological events in which mineralized chitinous structures are built and degraded. These events are in turn governed by genes whose patterns of expression are presumably linked to the molting cycle. To study these genes we performed next generation sequencing and constructed a molt-related transcriptomic library from two exoskeletal-forming tissues of the crayfish Cherax quadricarinatus, namely the gastrolith and the mandible cuticle-forming epithelium. To simplify the study of such a complex process as molting, a novel approach, binary patterning of gene expression, was employed. This approach revealed that key genes involved in the synthesis and breakdown of chitin exhibit a molt-related pattern in the gastrolith-forming epithelium. On the other hand, the same genes in the mandible cuticle-forming epithelium showed a molt-independent pattern of expression. Genes related to the metabolism of glucosamine-6-phosphate, a chitin precursor synthesized from simple sugars, showed a molt-related pattern of expression in both tissues. The binary patterning approach unfolds typical patterns of gene expression during the molt cycle of a crustacean. The use of such a simplifying integrative tool for assessing gene patterning seems appropriate for the study of complex biological processes.

Characterization of a novel RXR receptor in the salmon louse (Lepeophtheirus salmonis, Copepoda) regulating growth and female reproduction

BACKGROUND

Nuclear receptors have crucial roles in all metazoan animals as regulators of gene transcription. A wide range of studies have elucidated molecular and biological significance of nuclear receptors but there are still a large number of animals where the knowledge is very limited. In the present study we have identified an RXR type of nuclear receptor in the salmon louse (Lepeophtheirus salmonis) (i.e. LsRXR). RXR is one of the two partners of the Ecdysteroid receptor in arthropods, the receptor for the main molting hormone 20-hydroxyecdysone (E20) with a wide array of effects in arthropods.

RESULTS

Five different LsRXR transcripts were identified by RACE showing large differences in domain structure. The largest isoforms contained complete DNA binding domain (DBD) and ligand binding domain (LBD), whereas some variants had incomplete or no DBD. LsRXR is transcribed in several tissues in the salmon louse including ovary, subcuticular tissue, intestine and glands. By using Q-PCR it is evident that the LsRXR mRNA levels vary throughout the L. salmonis life cycle. We also show that the truncated LsRXR transcript comprise about 50% in all examined samples. We used RNAi to knock-down the transcription in adult reproducing female lice. This resulted in close to zero viable offspring. We also assessed the LsRXR RNAi effects using a L. salmonis microarray and saw significant effects on transcription in the female lice. Transcription of the major yolk proteins was strongly reduced by knock-down of LsRXR. Genes involved in lipid metabolism and transport were also down regulated. Furthermore, different types of growth processes were up regulated and many cuticle proteins were present in this group.

CONCLUSIONS

The present study demonstrates the significance of LsRXR in adult female L. salmonis and discusses the functional aspects in relation to other arthropods. LsRXR has a unique structure that should be elucidated in the future.

Identification of potential markers and sensitive tissues for low or high salinity stress in an intertidal mud crab (Macrophthalmus japonicus)

Macrophthalmus japonicus is an intertidal mud crab is an ecologically important species in Korea, can tolerate a wide range of natural and anthropogenic stressors. Environmental changes especially salinity cause physiological stress to the marine habitats. Differential gene transcription of M. japonicus tissues provided information about tissue specific responses against salinity. Five potential genes were identified and their transcription levels were determined quantitatively comparison to seawater (SW: 31 ± 1 psu) in M. japonicus gills and hepatopancreas after exposed them to different salinities. Ecdysteroid receptor (Mj-EcR), trypsin (Mj-Tryp), arginine kinase (Mj-AK), lipopolysaccharide and β-1,3-glucan binding protein (Mj-LGBP) and peroxinectin (Mj-Prx) in hepatopancreas up-regulated against different salinities. In contrast, the gills, Mj-EcR, Mj-Tryp and Mj-AK showed late up-regulated responses to 40 psu compared to SW. All genes except Mj-LGBP showed up regulation in the gills as time dependent manner. These genes can be considered as potential markers to assess responses in salinity changes. This study suggests hepatopancreas is a suitable tissue for transcriptional, biochemical and physiological responses analysis on M. japonicus in low and high salinity stress.

Alternative splicing in the fiddler crab cognate ecdysteroid receptor: variation in receptor isoform expression and DNA binding properties in response to hormone

RXR cDNA cloning from three Uca species led to the identification of 4 conserved isoforms, indicative of alternative splicing in the hinge and ligand binding domains (LBD). Sequencing of overlapping clones from a Ucapugilator genomic library identified EcR isoforms matching previously identified cDNA variants; in addition, a cryptic exon in the LBD was detected and evidence for expression of this new isoform was obtained from next-generation sequencing. RNA-seq analysis also identified a new amino terminal EcR variant. EcR and RXR transcript abundance increases throughout ovarian maturation in U. pugilator, while cognate receptor transcript abundance remains constant in a related Indo-Pacific species with a different reproductive strategy. To examine if crab RXR LBD isoforms have different physical properties in vitro, electromobility shift assays were performed with different EcR isoforms. The cognate crab and fruit fly receptors differ in their responses to hormone. Ecdysteroids did not increase DNA binding for the crab heterodimers, while ecdysteroids stimulate binding for Drosophilamelanogaster EcR/USP heterodimers. In swapping experiments, UpEcR/USP heterodimers did not show ligand-responsive differences in DNA binding; both crab RXR LBD isoforms, however, conferred ligand-responsive increases in DNA binding with DmEcRs. These data indicate that both UpRXR LBD isoforms can heterodimerize with the heterologous DmEcR receptors and promote ligand and DNA binding. Unresponsiveness of the cognate receptors to ecdysteroid, however, suggest additional factors may be required to mediate endogenous, perhaps isoform-specific, differences in EcR conformation, consistent with previously reported effects of UpRXR isoforms on UpEcR ligand-binding affinities.

Expression of cytoskeletal and molt-related genes is temporally scheduled in the hypodermis of the crayfish Procambarus clarkii during premolt

The rigid crustacean exoskeleton, the cuticle, is composed of the polysaccharide chitin, structural proteins and mineral deposits. It is periodically replaced to enable growth and its construction is an energy-demanding process. Ecdysis, the shedding event of the old cuticle is preceded by a preparatory phase, termed premolt, in which the present cuticle is partially degraded and a new one is formed underneath it. Procambarus clarkii (Girard), an astacid crustacean, was used here to comprehensively examine the changing patterns of gene expression in the hypodermis underlying the cuticle of the carapace at seven time points along ~14 premolt days. Next generation sequencing was used to construct a multi-tissue P. clarkii transcript sequence assembly to be generally used in a variety of transcriptomic studies. An aimed reference transcriptome was created here for the performance of a digital transcript expression analysis, determining the gene expression profiles in each of the examined premolt stages. The analysis revealed a cascade of sequential expression events of molt-related genes involved in chitin degradation, synthesis and modification, as well as synthesis of collagen and four groups of cuticular structural genes. The novel description of major transcriptional events during premolt and determination of their timing provide temporal markers for future studies of molt progress and regulation. The peaks of expression of the molt-related genes were preceded by expression peaks of cytoskeletal genes hypothesized to be essential for premolt progress by regulating protein synthesis and/or transport probably by remodeling the cytoskeletal structure.

Crustacean oxi-reductases protein sequences derived from a functional genomic project potentially involved in ecdysteroid hormones metabolism - a starting point for function examination

A transcriptomic assembly originated from hypodermis and Y organ of the crustacean Pontastacus leptodactylus is used here for in silico characterization of oxi-reductase enzymes potentially involved in the metabolism of ecdysteroid molting hormones. RNA samples were extracted from male Y organ and its neighboring hypodermis in all stages of the molt cycle. An equimolar RNA mix from all stages was sequenced using next generation sequencing technologies and de novo assembled, resulting with 74,877 unique contigs. These transcript sequences were annotated by examining their resemblance to all GenBank translated transcripts, determining their Gene Ontology terms and their characterizing domains. Based on the present knowledge of arthropod ecdysteroid metabolism and more generally on steroid metabolism in other taxa, transcripts potentially related to ecdysteroid metabolism were identified and their longest possible conceptual protein sequences were constructed in two stages, correct reading frame was deduced from BLASTX resemblances, followed by elongation of the protein sequence by identifying the correct translation frame of the original transcript. The analyzed genes belonged to several oxi-reductase superfamilies including the Rieske non heme iron oxygenases, cytochrome P450s, short-chained hydroxysteroid oxi-reductases, aldo/keto oxireductases, lamin B receptor/sterol reductases and glucose-methanol-cholin oxi-reductatses. A total of 68 proteins were characterized and the most probable participants in the ecdysteroid metabolism where indicated. The study provides transcript and protein structural information, a starting point for further functional studies, using a variety of gene-specific methods to demonstrate or disprove the roles of these proteins in relation to ecdysteroid metabolism in P. leptodactylus.

Ecdysone receptor gene from the freshwater prawn Macrobrachium nipponense: identification of different splice variants and sexually dimorphic expression, fluctuation of expression in the molt cycle and effect of eyestalk ablation

The full-length cDNA of an ecdysone receptor gene (MnEcR) from Macrobrachium nipponense was cloned and the expression of the gene was investigated. MnEcR maintained a relatively low expression level in the early stages of embryos, but from nauplius stage, a steady increase in MnEcR expression was detected, it had the highest expression level in zoea stage. MnEcR was highly expressed in the hepatopancreas and gills among ten different tissues examined. MnEcR was rapidly upregulated in the premolt stage and rapidly downregulated in the postmolt stage. The expression of MnEcR was remarkably downregulated after eyestalk ablation in M. nipponense. An 18-amino-acid insertion/deletion and a 49-amino-acid substitution were found in the coding region of MnEcR, resulting in four splice variants: MnEcR-L1, -L2, -S1 and-S2. The expression of four splice variants of MnEcR in gonads was investigated using RT-PCR. Interestingly, the expression patterns of these splice variants differed between males and females. The dominant splice variants in testis were MnEcR-S1 and -S2, while in ovary they were MnEcR-L1 and -S2, indicating specific roles for these splice variants in male and female individuals.

Six chitinases from oriental river prawn Macrobrachium nipponense: cDNA characterization, classification and mRNA expression during post-embryonic development and moulting cycle

Chitinase plays crucial physiological roles in crustaceans, including the digestion of chitin-containing food, moulting and the defense of shrimp against viruses. However, in contrast to insect species, no genome-wide analysis has been carried out in crustacean species and cDNAs encoding chitinase and chitinase-like proteins have been characterized in relatively few species. In this study, we identified six chitinase genes in the oriental river prawn, Macrobrachium nipponense, according to the established expressed sequence tag (EST) information using Rapid Amplification of the cDNA Ends (RACE) technique and homology cloning. We assigned these genes to three different chitinase groupings, which were designated MnCht1A, 1B, 3A, 3B, 3C and 4. The domain organization analysis of the six MnCht proteins revealed that only MnCht3C and MnCht4 possessed full structure, while MnCht1A, 1B, 3A and 3B lacked the serine/threonine (S/T)-rich linker and chitin-binding domains (CBDs). Their expression in different tissues and different developmental stages suggested that all of them have a function in the digestion of chitinous foods, modification of gut peritrophic membrane and degradation of the chitin exoskeleton. Analysis of the stage-specific moulting cycle and different temperature stimulation provided further evidence that MnCht1A, 1B and 3B have pivotal roles in the moulting cycle, while MnCht 4 only assists in the moulting process. This study provides important information for further investigations on the functions of chitinase in M. nipponense and other crustaceans.

Application of D-Crustacean Hyperglycemic Hormone Induces Peptidases Transcription and Suppresses Glycolysis-Related Transcripts in the Hepatopancreas of the Crayfish Pontastacus leptodactylus - Results of a Transcriptomic Study

The crustacean Hyperglycemic Hormone (cHH) is a neuropeptide present in many decapods. Two different chiral isomers are simultaneously present in Astacid crayfish and their specific biological functions are still poorly understood. The present study is aimed at better understanding the potentially different effect of each of the isomers on the hepatopancreatic gene expression profile in the crayfish Pontastacus leptodactylus, in the context of short term hyperglycemia. Hence, two different chemically synthesized cHH enantiomers, containing either L- or D-Phe(3), were injected to the circulation of intermolt females following removal of their X organ-Sinus gland complex. The effects triggered by the injection of the two alternate isomers were detected after one hour through measurement of circulating glucose levels. Triggered changes of the transcriptome expression profile in the hepatopancreas were analyzed by RNA-seq. A whole transcriptome shotgun sequence assembly provided the assumedly complete transcriptome of P. leptodactylus hepatopancreas, followed by RNA-seq analysis of changes in the expression level of many genes caused by the application of each of the hormone isomers. Circulating glucose levels were much higher in response to the D-isoform than to the L-isoform injection, one hour from injection. Similarly, the RNA-seq analysis confirmed a stronger effect on gene expression following the administration of D-cHH, while just limited alterations were caused by the L-isomer. These findings demonstrated a more prominent short term effect of the D-cHH on the transcription profile and shed light on the effect of the D-isomer on specific functional gene groups. Another contribution of the study is the construction of a de novo assembly of the hepatopancreas transcriptome, consisting of 39,935 contigs, that dramatically increases the molecular information available for this species and for crustaceans in general, providing an efficient tool for studying gene expression patterns in this organ.

Hemocyanin with phenoloxidase activity in the chitin matrix of the crayfish gastrolith

Gastroliths are transient extracellular calcium deposits formed by the crayfish Cherax quadricarinatus von Martens on both sides of the stomach wall during pre-molt. Gastroliths are made of a rigid chitinous organic matrix, constructed as sclerotized chitin-protein microfibrils within which calcium carbonate is deposited. Although gastroliths share many characteristics with the exoskeleton, they are simpler in structure and relatively homogeneous in composition, making them an excellent cuticle-like model for the study of cuticular proteins. In searching for molt-related proteins involved in gastrolith formation, two integrated approaches were employed, namely the isolation and mass spectrometric analysis of proteins from the gastrolith matrix, and 454-sequencing of mRNAs from both the gastrolith-forming and sub-cuticular epithelia. SDS-PAGE separation of gastrolith proteins revealed a set of bands at apparent molecular masses of 75-85 kDa; mass spectrometry data matched peptide sequences from the deduced amino acid sequences of seven hemocyanin transcripts. This assignment was then examined by immunoblot analysis using anti-hemocyanin antibodies, also used to determine the spatial distribution of the proteins in situ. Apart from contributing to oxygen transport, crustacean hemocyanins were previously suggested to be involved in several aspects of the molt cycle, including hardening of the new post-molt exoskeleton via phenoloxidation. The phenoloxidase activity of gastrolith hemocyanins was demonstrated. It was also noted that hemocyanin transcript expression during pre-molt was specific to the hepatopancreas. Our results thus reflect a set of functionally versatile proteins, expressed in a remote metabolic tissue and dispersed via the hemolymph to perform different roles in various organs and structures.

Stimulation of molt by RNA interference of the molt-inhibiting hormone in the crayfish Cherax quadricarinatus

In crustaceans, molting is known to be under the control of neuropeptide hormones synthesized and secreted from the eyestalk ganglia. While the role of molt-inhibiting hormone (MIH) in regulating molting has been described in several species using classical methods, an in vivo specific MIH targeted manipulation has not been described yet. In the present study, an MIH cDNA was isolated and sequenced from the eyestalk ganglia of the Australian freshwater red claw crayfish Cherax quadricarinatus (Cq) by 5' and 3' RACE. We analyzed the putative Cq-MIH based on sequence homology, a three dimensional structure model and transcript's tissue specificity. We further examined the involvement of Cq-MIH in the control of molt in the crayfish through RNAi by in vivo injections of Cq-MIH double-stranded RNA, which resulted in, similarly to eyestalk ablation, acceleration of molt cycles. This acceleration was reflected by a significant reduction (up to 32%) in molt interval and an increased rate in molt mineralization index (MMI), which correlated with the induction of ecdysteroid hormones compared to control. Altogether, this study provides a proof of function for the involvement of the Cq-MIH gene in molt regulation in the crayfish.

Five hepatopancreatic and one epidermal chitinases from a pandalid shrimp (Pandalopsis japonica): cloning and effects of eyestalk ablation on gene expression

Six cDNAs encoding chitinase proteins in Pandalopsis japonica were isolated by using polymerase chain reaction (PCR) cloning methods and bioinformatic analysis of expressed sequence tags (ESTs). The cDNAs, designated Pj-Cht1, 2, 3A, 3B, 3C, and 4, encoded proteins ranging from 388 to 607 amino acid residues in length (43.61-67.62kDa) and displayed a common structural organization: an N-terminal catalytic domain, a Thr/Pro-rich linker region, and either 0 (Pj-Cht2, 3A), 1 (Pj-Cht1, 3B, and 3C), or 2 (Pj-Cht4) C-terminal chitin-binding domain(s) (CBD). Pj-Cht1 and 2 lacked the 5' end of the open reading frame (ORF); the other Pj-Chts contained the complete ORF. All known decapod crustacean chitinases were segregated into at least four groups based on phylogenetic analysis and domain organization. Group 1 chitinases, represented by Pj-Cht1, were most closely related to insect group I chitinases and may function in the digestion of the peritrophic membrane. Group 2 chitinases including Pj-Cht2 show different domain organizations and pI value from other chitinases and appear to function in degradation of the old exoskeleton during the premolt period. Group 3 chitinases, represented by Pj-Cht3A, 3B, and 3C, may function in digestion of chitin-containing food and defense against pathogens. Group 4 chitinases, represented by Pj-Cht4, have two CBDs and their functions are unknown. Five Pj-Chts (Pj-Cht1, 3A, 3B, 3C, and 4) are expressed in the hepatopancreas and intestine, whereas Pj-Cht2 is expressed in epidermis and SG/XO complex suggesting crustacean chitinases can be classified into two groups (hepatopancreatic and epidermal) based on the expression profile. Eyestalk ablation (ESA) down-regulated the hepatopancreatic chitinase expression (Pj-Cht1, 3A, and 3C); Pj-Cht3B expression was not significantly affected by ESA. By contrast, mRNA levels of Pj-Cht2 were significantly upregulated in 7days post-ESA. Pj-Cht4 mRNA levels were too low for measurement with quantitative polymerase chain reaction. ESA had no significant effect on chitinase expression in the intestine. These data indicate that Pj-Cht1, 3A, 3B, 3C, and 4 are hepatopancreatic chitinases that may function in the digestion of ingested chitin and the modification of peritrophic membrane in the intestine. By contrast, epidermal chitinase, Pj-Cht2 may play a role in chitin metabolism during molt cycle as shown in other crustacean group 2 chitinases.

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃ biomineral in crayfish gastroliths

Bioavailable calcium is maintained by some crustaceans, in particular freshwater crayfish, by stabilizing amorphous calcium carbonate (ACC) within reservoir organs--gastroliths, readily providing the Ca(2+) needed to build a new exoskeleton. Despite the key scientific and biomedical importance of the in situ molecular-level picture of biogenic ACC and its stabilization in a bioavailable form, its description has eluded efforts to date. Herein, using multinuclear NMR, we accomplish in situ molecular-level characterization of ACC within intact gastroliths of the crayfish Cherax quadricarinatus. In addition to the known CaCO(3), chitin scaffold and inorganic phosphate (Pi), we identify within the gastrolith two primary metabolites, citrate and phosphoenolpyruvate (PEP) and quantify their abundance by applying solution NMR techniques to the gastrolith "soluble matrix." The long-standing question on the physico-chemical state of ACC stabilizing, P-bearing moieties within the gastrolith is answered directly by the application of solid state rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) NMR to the intact gastroliths: Pi and PEP are found molecularly dispersed throughout the ACC as a solid solution. Citrate carboxylates are found < 5 Å from a phosphate (intermolecular CP distance), an interaction that must be mediated by Ca(2+). The high abundance and extensive interactions of these molecules with the ACC matrix identify them as the central constituents stabilizing the bioavailable form of calcium. This study further emphasizes that it is imperative to characterize the intact biogenic CaCO(3). Solid state NMR spectroscopy is shown to be a robust and accessible means of determining composition, internal structure, and molecular functionality in situ.

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.

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.

Differential gene expression during the moult cycle of Antarctic krill (Euphausia superba)

Background

All crustaceans periodically moult to renew their exoskeleton. In krill this involves partial digestion and resorption of the old exoskeleton and synthesis of new cuticle. Molecular events that underlie the moult cycle are poorly understood in calcifying crustaceans and even less so in non-calcifying organisms such as krill. To address this we constructed an Antarctic krill cDNA microarray in order to generate gene expression profiles across the moult cycle and identify possible activation pathways.

Results

A total of 26 different cuticle genes were identified that showed differential gene expression across the moult cycle. Almost all cuticle genes were up regulated during premoult and down regulated during late intermoult. There were a number of transcripts with significant sequence homology to genes potentially involved in the synthesis, breakdown and resorption of chitin. During early premoult glutamine synthetase, a gene involved in generating an amino acid used in the synthesis of glucosamine, a constituent of chitin, was up regulated more than twofold. Mannosyltransferase 1, a member of the glycosyltransferase family of enzymes that includes chitin synthase was also up regulated during early premoult. Transcripts homologous to a β-N-acetylglucosaminidase (β-NAGase) precursor were expressed at a higher level during late intermoult (prior to apolysis) than during premoult. This observation coincided with the up regulation during late intermoult, of a coatomer subunit epsilon involved in the production of vesicles that maybe used to transport the β-NAGase precursors into the exuvial cleft. Trypsin, known to activate the β-NAGase precursor, was up regulated more than fourfold during premoult. The up regulation of a predicted oligopeptide transporter during premoult may allow the transport of chitin breakdown products across the newly synthesised epi- and exocuticle layers.

Conclusion

We have identified many genes differentially expressed across the moult cycle of krill that correspond with known phenotypic structural changes. This study has provided a better understanding of the processes involved in krill moulting and how they may be controlled at the gene expression level.

Suitability of the clonal marbled crayfish for biogerontological research: a review and perspective, with remarks on some further crustaceans

This article examines the suitability of the parthenogenetic marbled crayfish for research on ageing and longevity. The marbled crayfish is an emerging laboratory model for development, epigenetics and toxicology that produces up to 400 genetically identical siblings per batch. It is easily cultured, has an adult size of 4-9 cm, a generation time of 6-7 months and a life span of 2-3 years. Experimental data and biological peculiarities like isogenicity, direct development, indeterminate growth, high regeneration capacity and negligible senescence suggest that the marbled crayfish is particularly suitable to investigate the dependency of ageing and longevity from non-genetic factors such as stochastic developmental variation, allocation of metabolic resources, damage and repair, caloric restriction and social stress. It is also well applicable to examine alterations of the epigenetic code with increasing age and to identify mechanisms that keep stem cells active until old age. As a representative of the sparsely investigated crustaceans and of animals with indeterminate growth and extended brood care the marbled crayfish may even contribute to evolutionary theories of ageing and longevity. Some relatives are recommended as substitutes for investigation of topics, for which the marbled crayfish is less suitable like genetics of ageing and achievement of life spans of decades under conditions of low food and low temperature. Research on ageing in the marbled crayfish and its relatives is of practical relevance for crustacean fisheries and aquaculture and may offer starting points for the development of novel anti-ageing interventions in humans.

The effects of farnesoic acid and 20-hydroxyecdysone on vitellogenin gene expression in the lobster, Homarus americanus, and possible roles in the reproductive process

Reproduction in female lobster (Homarus americanus) is characterized by the maturation of the ovary, with a gradual increase in its size as a result of uptake of yolk protein precursor, vitellogenin (Vg) to the final product vitellin (Vn). Vn is formed by aggregation of several Vg subunits. In most decapods, the hepatopancreas is the major site of vitellogenin biosynthesis. The production of vitellogenin is controlled by endocrine factors. In this study, the effect of farnesoic acid (FA) and 20-hydroxyecdysone (20E) on production of vitellogenin by hepatopancreas (HaVg1) was investigated by in vitro organ explant HaVg1 gene expression was stimulated by FA or 20E in a dose-dependent manner. A 2-fold and 2.2-fold increase in HaVg1 gene expression was observed with 4.2 microM FA and 0.7 microM 20E, respectively. The stimulatory effect by either FA or 20E was observed principally during the first 90 min. Stimulation of HaVg1 gene expression by FA and 20E together is greater (3.3-fold increase) than that of either hormone alone. This stimulation was also observed within the first 90 min. To study the synergistic effect of these two hormones, FA and 20E were tested separately and together at low concentration (42.3 nM and 6.7 nM, respectively). Combined use of FA and 20E increased HaVg1 gene expression synergistically, but not additively. These findings should contribute to our understanding of lobster reproduction and provide insights into manipulation of lobster reproduction in aquaculture or under captive conditions.

A protein involved in the assembly of an extracellular calcium storage matrix

Gastroliths, the calcium storage organs of crustaceans, consist of chitin-protein-mineral complexes in which the mineral component is stabilized amorphous calcium carbonate. To date, only three proteins, GAP 65, gastrolith matrix protein (GAMP), and orchestin, have been identified in gastroliths. Here, we report a novel protein, GAP 10, isolated from the gastrolith of the crayfish Cherax quadricarinatus and specifically expressed in its gastrolith disc. The encoding gene was cloned by partial sequencing of the protein extracted from the gastrolith matrix. Based on an assembled microarray cDNA chip, GAP 10 transcripts were found to be highly (12-fold) up-regulated in premolt gastrolith disc and significantly down-regulated in the hypodermis at the same molt stage. The deduced protein sequence of GAP 10 lacks chitin-binding domains and does not show homology to known proteins in the GenBank data base. It does, however, have an amino acid composition that has similarity to proteins extracted from invertebrate and ascidian-calcified extracellular matrices. The GAP 10 sequence contains a predicted signal peptide and predicted phosphorylation sites. In addition, the protein is phosphorylated and exhibits calcium-binding ability. Repeated daily injections of GAP 10 double strand RNA to premolt C. quadricarinatus resulted in a prolonged premolt stage and in the development of gastroliths with irregularly rough surfaces. These findings suggest that GAP 10 may be involved in the assembly of the gastrolith chitin-protein-mineral complex, particularly in the deposition of amorphous calcium carbonate.

Molt cycle regulation of protein synthesis in skeletal muscle of the blackback land crab, Gecarcinus lateralis, and the differential expression of a myostatin-like factor during atrophy induced by molting or unweighting

In decapod crustaceans, claw muscle undergoes atrophy in response to elevated ecdysteroids while thoracic muscle undergoes atrophy in response to unweighting. The signaling pathways that regulate muscle atrophy in crustaceans are largely unknown. Myostatin is a negative regulator of muscle growth in mammals, and a myostatin-like cDNA is preferentially expressed in muscle of the land crab, Gecarcinus lateralis (Gl-Mstn). Contrary to prediction, levels of Gl-Mstn mRNA decreased dramatically in both the claw closer and weighted thoracic muscles when molting was induced by either eyestalk ablation (ESA) or multiple limb autotomy (MLA). However, the effect of molt induction was greater in the claw muscle. By late premolt, Gl-Mstn mRNA in the claw muscle decreased 81% and 94% in ESA and MLA animals, respectively, and was negatively correlated with ecdysteroids. Gl-Mstn mRNA in thoracic muscle decreased 68% and 82% in ESA and MLA animals, respectively, but was only weakly correlated with ecdysteroid. Claw and thoracic muscles also differed to varying extents in the expression of ecdysteroid receptor (Gl-EcR and Gl-RXR), elongation factor-2 (Gl-EF-2), and calpain T (Gl-CalpT) in response to molt induction, but levels of the four transcripts were not correlated with ecdysteroid. The downregulation of Gl-Mstn expression in premolt claw muscle coincided with 11- and 13-fold increases in protein synthesis in the myofibrillar and soluble protein fractions, respectively. Furthermore, the rate of the increase in the synthesis of soluble proteins was greater than that of myofibrillar proteins during early premolt (1.4:1, soluble:myofibrillar), but the two were equivalent during late premolt. By contrast, Gl-Mstn mRNA increased 3-fold and Gl-CalpT mRNA decreased 40% in unweighted thoracic muscle; there was little or no effect on Gl-EF-2, Gl-EcR, and Gl-RXR mRNA levels. These data indicate that Gl-Mstn expression is negatively regulated by both ecdysteroids and load-bearing contractile activity. The downregulation of Gl-Mstn in claw muscle may induce the elevated protein turnover associated with remodeling of the contractile apparatus during molt-induced atrophy. The upregulation of Gl-Mstn in unweighted thoracic muscle suggests that this factor is also involved in disuse atrophy when hemolymph ecdysteroid levels are low.

Growth and moulting in Northern krill (Meganyctiphanes norvegica Sars)

Moulting and growth as a key aspect of the life-history of crustaceans has been reviewed here for Meganyctiphanes norvegica. Moulting is a cyclical process with relatively constrained, uniform phases that have been well documented. The crustacean moult cycle has a large influence on growth-rates, reproduction and metabolism. Moult and growth are under hormonal control with further environmental influences. A pre-requisite for intensive studies is a detailed moult staging system. Here, a further refinement and temporal phasing is presented for M. norvegica. On such a basis, the dynamics of cuticle synthesis and degradation are shown. Moult and reproductive cycles are interlinked and krill is able to combine growth and reproduction in a way that allows females to achieve similar net growth rates to males. A synchronisation of physiological processes and behaviour related to growth and reproduction enhances environmental success. Moult staging can also be used to assess growth rates in the field. Some further technical approaches are reviewed. Laboratory maintenance and field data are combined to determine growth rates under various environmental conditions. These are related to life-growth assessments from population studies comparing krill along a latitudinal gradient. Life-cycle and physiological data indicate that Northern krill are able to cope with both warm and cold environments and have highly adaptable phenotypes. The species may serve as useful indicator of environmental change. Its potential proliferation in new environments may also have implications to regional food webs, given the krill's high level of growth and productivity and their pivotal trophic role.

How to minimize formation and growth of tumours: potential benefits of decapod crustaceans for cancer research

Tumours have only rarely been observed in the decapod crustaceans, a large animal group of more than 10,000 species that includes the commercially important and well investigated shrimp, lobsters, crayfish and crabs. Analysis of the literature and information from cancer and diseases data bases revealed a total of 15 incidences, some of them being questionable. Even in the long-lived species, which can reach life spans of almost 100 years, neoplasias are virtually unknown. The data published so far suggest that the strikingly different frequencies of carcinogenesis between decapods and other well investigated animal groups like mammals, fish, insects and molluscs is based on differences of the metabolic pathways for carcinogens, the immune systems, and the regulation of stem cells. Therefore, representatives of the Decapoda may serve as useful models to study how organisms can successfully prevent or control spontaneously and environmentally induced cell proliferation. A particularly promising candidate for in-depth investigation of these topics is the marbled crayfish, a rather new clonal lineage that is presently being introduced as a laboratory model in development and epigenetics.

A gastrolith protein serving a dual role in the formation of an amorphous mineral containing extracellular matrix

Despite the proclamation of Lowenstam and Weiner that crustaceans are the "champions of mineral mobilization and deposition of the animal kingdom," relatively few proteins from the two main calcification sites in these animals, i.e., the exoskeleton and the transient calcium storage organs, have been identified, sequenced, and their roles elucidated. Here, a 65-kDa protein (GAP 65) from the gastrolith of the crayfish, Cherax quadricarinatus, is fully characterized and its function in the mineralization of amorphous calcium carbonate (ACC) of the extracellular matrix is demonstrated. GAP 65 is a negatively charged glycoprotein that possesses three predicted domains: a chitin-binding domain 2, a low-density lipoprotein receptor class A domain, and a polysaccharide deacetylase domain. Expression of GAP 65 was localized to columnar epithelial cells of the gastrolith disk during premolt. In vivo administration of GAP 65 dsRNA resulted in a significant reduction of GAP 65 transcript levels in the gastrolith disk. Such gene silencing also caused dramatic structural and morphological deformities in the chitinous-ACC extracellular matrix structure. ACC deposited in these gastroliths appeared to be sparsely packed with large elongated cavities compared with the normal gastrolith, where ACC is densely compacted. ACC spherules deposited in these gastroliths are significantly larger than normal. GAP 65, moreover, inhibited calcium carbonate crystallization in vitro and stabilized synthetic ACC. Thus, GAP 65 is the first protein shown to have dual function, involved both in extracellular matrix formation and in mineral deposition during biomineralization.

Reciprocal changes in calcification of the gastrolith and cuticle during the molt cycle of the red claw crayfish Cherax quadricarinatus

Mobilization of calcium during the molt cycle from the cuticle to transient calcium deposits is widely spread in crustaceans. The dynamics of calcium transport to transient calcium deposits called gastroliths and to the cuticle over the course of the molt cycle were studied in the crayfish Cherax quadricarinatus. In this species, calcium was deposited in the gastroliths during premolt and transported back to the cuticle during postmolt, shown by digital X-ray radiograph analysis. The predominant mineral in the crayfish is amorphous calcium carbonate embedded in an organic matrix composed mainly of chitin. Scanning electron micrographs of the cuticle during premolt showed that the endocuticle and parts of the exocuticle were the source of most of the labile calcium, while the epicuticle did not undergo degradation and remained mineralized throughout the molt cycle. The gastroliths are made of concentric layers of amorphous calcium carbonate intercalated between chitinous lamella. Measurements of pH and calcium levels during gastrolith deposition showed that calcium concentrations in the gastroliths, stomach, and muscle were about the same (10 to 11 mmol l(-1)). On the other hand, pH varied greatly, from 8.7+/-0.15 in the gastrolith cavity through 7.6+/-0.2 in muscle to 6.9+/-0.5 in the stomach.

Hepatopancreatic multi-transcript expression patterns in the crayfish Cherax quadricarinatus during the moult cycle

Alterations of hepatopancreatic multi-transcript expression patterns, related to induced moult cycle, were identified in male Cherax quadricarinatus through cDNA microarray hybridizations of hepatopancreatic transcript populations. Moult was induced by X-organ sinus gland extirpation or by repeated injections of 20-hydroxyecdysone. Manipulated males were sacrificed at premoult or early postmoult, and a reference population was sacrificed at intermoult. Differentially expressed genes among the four combinations of two induction methods and two moult stages were identified. Biologically interesting clusters revealing concurrently changing transcript expressions across treatments were selected, characterized by a general shift of expression throughout premoult and early postmoult vs. intermoult, or by different premoult vs. postmoult expressions. A number of genes were differentially expressed in 20-hydroxyecdysone-injected crayfish vs. X-organ sinus gland extirpated males.