Exoskeletal proteins from the crab, Cancer pagurus

Transcriptomic Analysis across Crayfish (Cherax quadricarinatus) Claw Regeneration Reveals Potential Stem Cell Sources for Cultivated Crustacean Meat

In the face of rising global demand and unsustainable production methods, cultivated crustacean meat (CCM) is proposed as an alternative means to produce delicious lobster, shrimp, and crab products. Cultivated meat requires starting stem cells that may vary in terms of potency and the propensity to proliferate or differentiate into myogenic (muscle-related) tissues. Recognizing that regenerating limbs are a non-lethal source of tissue and may harbor relevant stem cells, we selected those of the crayfish Cherax quadricarinatus as our model. To investigate stem cell activity, we conducted RNA-Seq analysis across six stages of claw regeneration (four pre-molt and two post-molt stages), along with histology and real-time quantitative PCR (qPCR). Our results showed that while genes related to energy production, muscle hypertrophy, and exoskeletal cuticle synthesis dominated the post-molt stages, growth factor receptors (FGFR, EGFR, TGFR, and BMPR) and those related to stem cell proliferation and potency (Cyclins, CDKs, Wnts, C-Myc, Klf4, Sox2, PCNA, and p53) were upregulated before the molt. Pre-molt upregulation in several genes occurred in two growth peaks; Stages 2 and 4. We therefore propose that pre-molt limb regeneration tissues, particularly those in the larger Stage 4, present a prolific and non-lethal source of stem cells for CCM development.

Exoskeleton protein repertoires in decapod crustaceans revealed distinct biomineralization evolution with molluscs

Crustaceans are the champions of mineral mobilization and deposition in the animal kingdom due to their unique ability to rapidly and periodically mineralize and demineralize their exoskeletons. They are commonly covered with mineralized exoskeletons for protection and regularly molt throughout their lives. Mineralized crustacean exoskeletons are formed under the control of macromolecules especially matrix proteins but the types of matrix proteins are understudied compared to those in molluscan shells. This gap hinders our understanding of their evolutionary paths compared with those of molluscs. Here, we comprehensively analyzed matrix proteins in the exoskeleton of two crabs, one shrimp, and one crayfish and resulted in a major improvement (∼10-fold) in the identification of biomineralization proteins compared to conventional methods for decapod crustaceans. By a comparison with well-studied molluscan biomineralization proteins, we found that decapod crustaceans evolved novel proteins to form mineralized exoskeletons while sharing some proteins with those of molluscs. Our study sheds light on their evolution and adaption to different environment for exoskeleton formation and provides a foundation for further studies of mineralization in crustaceans under normal and climate-changed conditions. SIGNIFICANCE: Most crustaceans have mineralized exoskeletons as protection. How they form these hierarchical structures is still unclear. This is due partially to the understudied matrix proteins in the minerals. This study filled such a gap by using proteomic analysis of matrix proteins from four decapod crustacean exoskeletons. Many novel proteins were discovered which enabled a solid comparison with those of molluscs. By comparison, we proposed that crustaceans evolved novel proteins to form mineralized exoskeletons while sharing some proteins with those of molluscs. This is useful for us to understand the evolution of two major biomineralized phylum.

Identifying the genes involved in the egg-carrying ovigerous hair development of the female blue crab Callinectes sapidus: transcriptomic and genomic expression analyses

BACKGROUND

Crustacean female sex hormone (CFSH) controls gradually developing adult female-specific morphological features essential for mating and brood care. Specifically, ovigerous hairs are developed during the prepuberty molt cycle of the blue crab Callinectes sapidus that are essential for carrying the eggs until they finish development. Reduced CFSH transcripts by CFSH-dsRNA injections result in fewer and shorter ovigerous hairs than the control. This study aimed to identify the specific genes responsible for ovigerous hair formation using transcriptomic, genomic and expression analyses of the ovigerous setae at three stages: prepuberty at early (OE) and late premolt (OL), and adult (AO) stages.

RESULTS

The de novo Trinity assembly on filtered sequence reads produced 96,684 Trinity genes and 124,128 transcripts with an N50 of 1,615 bp. About 27.3% of the assembled Trinity genes are annotated to the public protein sequence databases (i.e., NR, Swiss-Prot, COG, KEGG, and GO databases). The OE vs. OL, OL vs. AO, and OE vs. AO comparisons resulted in 6,547, 7,793, and 7,481 differentially expressed genes, respectively, at a log2-fold difference. Specifically, the genes involved in the Wnt signaling and cell cycle pathways are positively associated with ovigerous hair development. Moreover, the transcripts of ten cuticle protein genes containing chitin-binding domains are most significantly changed by transcriptomic analysis and RT-qPCR assays, which shows a molt-stage specific, down-up-down mode across the OE-OL-AO stages. Furthermore, the expression of the cuticle genes with the chitin-binding domain, Rebers and Riddiford domain (RR)-1 appears at early premolt, followed by RR-2 at late premolt stage. Mapping these 10 cuticle protein sequences to the C. sapidus genome reveals that two scaffolds with a 549.5Kb region and 35 with a 1.19 Mb region harbor 21 RR1 and 20 RR2 cuticle protein genes, respectively. With these findings, a putative mode of CFSH action in decapod crustaceans is proposed.

CONCLUSIONS

The present study describes a first step in understanding the mechanism underlying ovigerous hair formation in C. sapidus at the molecular level. Overall, demonstrating the first transcriptome analysis of crustacean ovigerous setae, our results may facilitate future studies into the decapod female reproduction belonging to the suborder Pleocyemata.

Characterization of cuticular proteins in CPR family in the wolf spider, Pardosa pseudoannulata, and the response of one subfamily genes to environmental stresses

Cuticular protein (CP) plays an essential role in the construction and function of exoskeleton in arthropods. CPR family, CP with Rebers and Riddiford (R&R) Consensus, is the largest CP family in insects, but it lacks systematic research in non-insect arthropods. In this study, we explored CPRs in the wolf spider, Pardosa pseudoannulata, a predator to many insect pests. We totally identified 152 CPRs in P. pseudoannulata genome, which were divided into two subgroups based on R&R Consensus sequences, with 12 CPRs in RR-1 and 140 in RR-2. All RR-2 members presented a novel Consensus with 34 amino acids, G-x(8)-G-x(6)-Y-x-A-x(3)-G-x(7)-N-E-x-G, which was a common characteristic for RR-2 CPRs in chelicerates. Transcriptome data was used to document the expression patterns of CPR genes in different tissues and ecdysis processes. The specific expressions were found for part CPR genes, such as five RR-2 genes that were specifically expressed in male genital bulbs and eleven RR-1 genes that were highly expressed in the integument. Due to the limited number and integument-specific expression of RR-1 genes, we further analyzed their responses to different environmental stresses at the transcriptional level. Except for PapsCPR11, ten RR-1 genes responded to at least one environmental stress, among with the expression of PapsCPR12 was significantly changed by three stresses (dryness, low temperature and imidacloprid treatments). Silencing PapsCPR12 increased the tolerance of P. pseudoannulata to imidacloprid. Overall, the results presented novel Consensus characteristics of CPRs in P. pseudoannulata, which was helpful for the identification and evolution analysis of CPRs in non-insect arthropods.

The genomics of phenotypically differentiated Asellus aquaticus cave, surface stream and lake ecotypes

Organisms well suited for the study of ecotype formation have wide distribution ranges, where they adapt to multiple drastically different habitats repeatedly over space and time. Here we study such ecotypes in a Crustacean model, Asellus aquaticus, a commonly occurring isopod found in freshwater habitats as diverse as streams, caves and lakes. Previous studies focusing on cave vs. surface ecotypes have attributed depigmentation, eye loss and prolonged antennae to several south European cave systems. Likewise, surveys across multiple Swedish lakes have identified the presence of dark-pigmented "reed" and light-pigmented "stonewort" ecotypes, which can be found within the same lake. In this study, we sequenced the first draft genome of A. aquaticus, and subsequently use this to map reads and call variants in surface stream, cave and two lake ecotypes. In addition, the draft genome was combined with a RADseq approach to perform a quantitative trait locus (QTL) mapping study using a laboratory bred F₂ and F₄ cave × surface intercross. We identified genomic regions associated with body pigmentation, antennae length and body size. Furthermore, we compared genome-wide differentiation between natural populations and found several genes potentially associated with these habitats. The assessment of the cave QTL regions in the light-dark comparison of lake populations suggests that the regions associated with cave adaptation are also involved with genomic differentiation in the lake ecotypes. These demonstrate how troglomorphic adaptations can be used as a model for related ecotype formation.

Transcriptome analysis of Neocaridina denticulate sinensis under copper exposure

Neocaridina denticulate sinensis is a small freshwater economic shrimp, as well as excellent laboratory model for their short life cycle and easy availability. However, the response of N. denticulate sinensis to pervasive copper pollution in aquatic environments has not been deeply investigated yet. Herein, we preformed Illumina sequencing technology to mine the alterations of cephalothorax transcriptome under 2.5 μmol/L of Cu²⁺ after 48 h. 122,512 unigenes were assembled and 219 unigenes were identified as significantly differentially expressed genes (DEGs) between control and Cu²⁺ treatment groups. Functional enrichment analysis revealed that DEGs were mostly associated with immune responses and molting, such as endocytosis, Fc gamma R-mediated phagocytosis and chitin metabolic process. Seven genes were chosen for qPCR verification, and the results showed that the transcriptome sequencing data were consistent with the qPCR results. This is the first report of transcriptome information about N. denticulate sinensis. These results provided a direction for the future research of resistance to Cu²⁺ in this shrimp, and simultaneously enriched gene information of N. denticulate sinensis.

Expected ocean warming conditions significantly alter the transcriptome of developing postlarval American lobsters (Homarus americanus): Implications for energetic trade-offs

The American lobster (Homarus americanus) is one of the most iconic and economically valuable fishery species in the Northwestern Atlantic. Surface ocean temperatures are rapidly increasing across much of the species' range, raising concern about resiliency in the face of environmental change. Warmer temperatures accelerate rates of larval development and enhance survival to the postlarval stage, but the potential costs at the molecular level have rarely been addressed. We explored how exposure to current summer temperatures (16 °C) or temperature regimes mimicking projected moderate or extreme warming scenarios (18 °C and 22 °C, respectively) for the Gulf of Maine during development influences the postlarval lobster transcriptome. After de novo assembling the transcriptome, we identified 2542 differentially expressed (DE; adjusted p < 0.05) transcripts in postlarvae exposed to 16 °C vs. 22 °C, and 422 DE transcripts in postlarvae reared at 16 °C vs. 18 °C. Lobsters reared at 16 °C significantly over-expressed transcripts related to cuticle formation and the immune response up to 14.4- and 8.5-fold respectively, relative to those reared at both 18 °C and 22 °C. In contrast, the expression of transcripts affiliated with metabolism increased up to 7.1-fold as treatment temperature increased. These results suggest that lobsters exposed to projected warming scenarios during development experience a shift in the transcriptome that reflects a potential trade-off between maintaining immune defenses and sustaining increased physiological rates under a warming environment. This could have major implications for post-settlement survival through increased risk of mortality due to disease and/or starvation if energetic demands cannot be met.

Transcriptome analysis on the exoskeleton formation in early developmetal stages and reconstruction scenario in growth-moulting in Litopenaeus vannamei

Exoskeleton construction is an important issue in shrimp. To better understand the molecular mechanism of exoskeleton formation, development and reconstruction, the transcriptome of the entire developmental process in Litopenaeus vannamei, including nine early developmental stages and eight adult-moulting stages, was sequenced and analysed using Illumina RNA-seq technology. A total of 117,539 unigenes were obtained, with 41.2% unigenes predicting the full-length coding sequence. Gene Ontology, Clusters of Orthologous Group (COG), the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and functional annotation of all unigenes gave a better understanding of the exoskeleton developmental process in L. vannamei. As a result, more than six hundred unigenes related to exoskeleton development were identified both in the early developmental stages and adult-moulting. A cascade of sequential expression events of exoskeleton-related genes were summarized, including exoskeleton formation, regulation, synthesis, degradation, mineral absorption/reabsorption, calcification and hardening. This new insight on major transcriptional events provide a deep understanding for exoskeleton formation and reconstruction in L. vannamei. In conclusion, this is the first study that characterized the integrated transcriptomic profiles cover the entire exoskeleton development from zygote to adult-moulting in a crustacean, and these findings will serve as significant references for exoskeleton developmental biology and aquaculture research.

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.

Natural Composite Systems for Bioinspired Materials

From a relatively limited selection of base materials, nature has steered the development of truly remarkable materials. The simplest and often overlooked organisms have demonstrated the ability to manufacture multi-faceted, molecular-level hierarchical structures that combine mechanical properties rarely seen in synthetic materials. Indeed, these natural composite systems, composed of an array of intricately arranged and functionally relevant organic and inorganic substances serve as inspiration for materials design. A better understanding of these composite systems, specifically at the interface of the hetero-assemblies, would encourage faster development of environmentally friendly "green" materials with molecular level specificities.

Crustacean-derived biomimetic components and nanostructured composites

Over millions of years, the crustacean exoskeleton has evolved into a rigid, tough, and complex cuticle that is used for structural support, mobility, protection of vital organs, and defense against predation. The crustacean cuticle is characterized by a hierarchically arranged chitin fiber scaffold, mineralized predominately by calcium carbonate and/or calcium phosphate. The structural organization of the mineral and organic within the cuticle occurs over multiple length scales, resulting in a strong and tough biological composite. Here, the ultrastructural details observed in three species of crustacean are reviewed: the American lobster (Homarus americanus), the edible crab (Cancer pagurus), and the peacock mantis shrimp (Odontodactylus scyllarus). The Review concludes with a discussion of recent advances in the development of biomimetics with controlled organic scaffolding, mineralization, and the construction of nanoscale composites, inspired by the organization and formation of the crustacean cuticle.

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.

Asaia accelerates larval development of Anopheles gambiae

Arthropod borne diseases cause significant human morbidity and mortality and, therefore, efficient measures to control transmission of the disease agents would have great impact on human health. One strategy to achieve this goal is based on the manipulation of bacterial symbionts of vectors. Bacteria of the Gram-negative, acetic acid bacterium genus Asaia have been found to be stably associated with larvae and adults of the Southeast Asian malaria vector Anopheles stephensi, dominating the microbiota of the mosquito. We show here that after the infection of Anopheles gambiae larvae with Asaia the bacteria were stably associated with the mosquitoes, becoming part of the microflora of the midgut and remaining there for the duration of the life cycle. Moreover they were passed on to the next generation through vertical transmission. Additionally, we show that there is an increase in the developmental rate when additional bacteria are introduced into the organism which leads us to the conclusion that Asaia plays a yet undetermined crucial role during the larval stages. Our microarray analysis showed that the larval genes that are mostly affected are involved in cuticle formation, and include mainly members of the CPR gene family.

Molt cycle related changes and effect of short term starvation on the biochemical constituents of the blue swimmer crab Portunus pelagicus

Synthesis and hardening of a new exoskeleton are essential to the arthropod molting process. The present study emphasizes the variations in the levels of hemolymph total free sugars, hepatopancreas glycogen and cuticular proteins during the molting stages of Portunus pelagicus. It also reports the effect of short-term starvation conditions on the biochemical constituents of the hemolymph. Intermolt crabs were subjected to 6 days of starvation and hemolymph samples were taken. Standard biochemical procedures were followed toward the quantification of total proteins, total free sugars and total lipids. The total free sugar level in the hemolymph of P. pelagicus was observed to increase during early premolt D0 (3.108 ± 0.032 g/ml) and a gradual decrease till late postmolt B stage (0.552 ± 0.124 g/ml), suggesting the need for total free sugars to provide energy for the apolysis process. Increase in the levels of hepatopancreas glycogen was observed from 1225 ± 0.04 μg/mg in early premolt D0 to 1700 ± 0.3 μg/mg in late premolt D2-3. This is in correlation with the decreased levels of free sugars during premolt stages, suggesting an increase in the storage of glycogen reserves in the hepatopancreas. Cuticular proteins increased during stage B (2.702 ± 0.093 g/ml) and stage C (3.065 ± 0.012 g/ml), indicating exoskeleton hardening and mineralization. Results of the starvation studies clearly showed a steady decline in the level of total free sugars till day 6 (0.099 ± 0.00 g/ml) when compared to the control (8.646 ± 0.08 g/ml). Gradual decrease of total lipids was also observed from the first day of the experiment (6.088 ± 2.44 g/ml) to the last day of the study (0.401 ± 0.20 g/ml) which was 85% lesser than the control (8.450 ± 0.49 g/ml)suggesting the efficient usage of total sugars to consolidate the loss of energy reserves during starvation. The knowledge of Molt-cycle events can be used as a tool for the evaluation of the developmental state providing a morphological reference system for physiological and biochemical studies related to crab aquaculture. Starvation studies enlightens that increasing carbohydrate levels in crab feed together with good protein content could alleviate the natural effects of starvation, improve farm productivity and reduce the deleterious impact of nitrogen pollution generated by rich-protein feeds used in crab farming.

Biomineralizations: insights and prospects from crustaceans

For growing, crustaceans have to molt cyclically because of the presence of a rigid exoskeleton. Most of the crustaceans harden their cuticle not only by sclerotization, like all the arthropods, but also by calcification. All the physiology of crustaceans, including the calcification process, is then linked to molting cycles. This means for these animals to find regularly a source of calcium ions quickly available just after ecdysis. The sources of calcium used are diverse, ranging from the environment where the animals live to endogenous calcium deposits cyclically elaborated by some of them. As a result, crustaceans are submitted to an important and energetically demanding calcium turnover throughout their life. The mineralization process occurs by precipitation of calcium carbonate within an organic matrix network of chitin-proteins fibers. Both crystalline and stabilized amorphous polymorphs of calcium carbonate are found in crustacean biominerals. Furthermore, Crustacea is the only phylum of animals able to elaborate and resorb periodically calcified structures. Notably for these two previous reasons, crustaceans are more and more extensively studied and considered as models of choice in the biomineralization research area.

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.

Mesostructure of the Exoskeleton of the Lobster Homarus Americanus

The exoskeleton of the lobsterHomarus americanusis a multiphase bio-composite which consists of a fibrous organic matrix (crystalline α-chitin and various types of non-crystalline proteins) and embedded biominerals (mainly calcite). In this study we present experimental data about the microscopic and mesoscopic structure of this material.

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.

Differential expression profiling of components associated with exoskeletal hardening in crustaceans

BACKGROUND

Exoskeletal hardening in crustaceans can be attributed to mineralization and sclerotization of the organic matrix. Glycoproteins have been implicated in the calcification process of many matrices. Sclerotization, on the other hand, is catalysed by phenoloxidases, which also play a role in melanization and the immunological response in arthropods. Custom cDNA microarrays from Portunus pelagicus were used to identify genes possibly associated with the activation pathways involved in these processes.

RESULTS

Two genes potentially involved in the recognition of glycosylation, the C-type lectin receptor and the mannose-binding protein, were found to display molt cycle-related differential expression profiles. C-type lectin receptor up-regulation was found to coincide with periods associated with new uncalcified cuticle formation, while the up-regulation of mannose-binding protein occurred only in the post-molt stage, during which calcification takes place, implicating both in the regulation of calcification. Genes presumed to be involved in the phenoloxidase activation pathway that facilitates sclerotization also displayed molt cycle-related differential expression profiles. Members of the serine protease superfamily, trypsin-like and chymotrypsin-like, were up-regulated in the intermolt stage when compared to post-molt, while trypsin-like was also up-regulated in pre-molt compared to ecdysis. Additionally, up-regulation in pre- and intermolt stages was observed by transcripts encoding other phenoloxidase activators including the putative antibacterial protein carcinin-like, and clotting protein precursor-like. Furthermore, hemocyanin, itself with phenoloxidase activity, displayed an identical expression pattern to that of the phenoloxidase activators, i.e. up-regulation in pre- and intermolt.

CONCLUSION

Cuticle hardening in crustaceans is a complex process that is precisely timed to occur in the post-molt stage of the molt cycle. We have identified differential expression patterns of several genes that are believed to be involved in biomineralization and sclerotization and propose possible regulatory mechanisms for these processes based on their expression profiles, such as the potential involvement of C-type lectin receptors and mannose binding protein in the regulation of calcification.

Influence of microstructure on deformation anisotropy of mineralized cuticle from the lobster Homarus americanus

The exoskeleton of the American lobster Homarus americanus is a hierarchically organized nano-composite material consisting of organic chitin-protein fibers associated with inorganic calcium carbonate. The presence of a well-developed and periodically arranged pore canal system leads to a honeycomb-like structure. The concomitant presence of the twisted plywood arrangement of the mineralized chitin-protein fibers alters the elastic properties, the deformation behavior, and fracture behavior compared to classical honeycomb structures. By performing compression tests in various directions of the cuticle we examined the anisotropic elastic-plastic deformation and fracture behavior of mineralized parts of the exoskeleton. By applying digital image correlation during compression testing, the evolution of the elastic-plastic deformation at the microscopic scale was observed with high resolution and simultaneously global stress and strain data were acquired. Shear tests were performed in order to determine the fracture energy for different shear planes and directions. The investigation of the microstructure after plastic deformation revealed the underlying deformation mechanisms of lobster endocuticle from the claws under different loading conditions. For evaluating the effect of hydration the samples were tested both in the dry and in the wet state.

Preferred crystallographic texture of alpha-chitin as a microscopic and macroscopic design principle of the exoskeleton of the lobster Homarus americanus

The crystallographic texture of the crystalline alpha-chitin matrix in the biological composite material forming the exoskeleton of the lobster Homarus americanus has been determined using synchrotron X-ray pole figure measurements and the calculation of orientation distribution functions. The study has two objectives. The first one is to elucidate crystallographic building principles via the preferred synthesis of certain orientations in crystalline organic tissue. The second one is to study whether a general global design principle exists for the exoskeleton which uses preferred textures relative to the local coordinate system throughout the lobster cuticle. The first point, hence, pursues the question of the extent to which and why alpha-chitin reveals preferred textures in the lobster cuticle. The second point addresses the question of why and whether such preferred textures (and the resulting anisotropy) exist everywhere in the exoskeleton. Concerning the first aspect, a strong preference of a fiber texture of the orthorhombic alpha-chitin is observed which is characterized by a 020 crystal axis normal to the exoskeleton surface for the chitin matrix. The second question is tackled by studying samples from different parts of the carapace. While the first aspect takes a microscopic perspective at the basic structure of the biological composite, the second point aims at building a bridge between an understanding of the microstructure and the macroscopic nature of a larger biological construction. We observe that the texture is everywhere in the carapace optimized in such a way that the same crystallographic axis of the chitin matrix is parallel to the normal to the local tangent plane of the carapace. Notable differences in the texture are observed between hard mineralized parts on the one hand and soft membranous parts on the other. The study shows that the complex hierarchical microstructure of the arthropod cuticle can be well described by surprisingly simple crystallographic textures.

Gene expression profiling of cuticular proteins across the moult cycle of the crab Portunus pelagicus

Background

Crustaceans represent an attractive model to study biomineralization and cuticle matrix formation, as these events are precisely timed to occur at certain stages of the moult cycle. Moulting, the process by which crustaceans shed their exoskeleton, involves the partial breakdown of the old exoskeleton and the synthesis of a new cuticle. This cuticle is subdivided into layers, some of which become calcified while others remain uncalcified. The cuticle matrix consists of many different proteins that confer the physical properties, such as pliability, of the exoskeleton.

Results

We have used a custom cDNA microarray chip, developed for the blue swimmer crab Portunus pelagicus, to generate expression profiles of genes involved in exoskeletal formation across the moult cycle. A total of 21 distinct moult-cycle related differentially expressed transcripts representing crustacean cuticular proteins were isolated. Of these, 13 contained copies of the cuticle_1 domain previously isolated from calcified regions of the crustacean exoskeleton, four transcripts contained a chitin_bind_4 domain (RR consensus sequence) associated with both the calcified and un-calcified cuticle of crustaceans, and four transcripts contained an unannotated domain (PfamB_109992) previously isolated from C. pagurus. Additionally, cryptocyanin, a hemolymph protein involved in cuticle synthesis and structural integrity, also displays differential expression related to the moult cycle. Moult stage-specific expression analysis of these transcripts revealed that differential gene expression occurs both among transcripts containing the same domain and among transcripts containing different domains.

Conclusion

The large variety of genes associated with cuticle formation, and their differential expression across the crustacean moult cycle, point to the complexity of the processes associated with cuticle formation and hardening. This study provides a molecular entry path into the investigation of the gene networks associated with cuticle formation.

Differential expression of eight transcripts and their roles in the cuticle of the blue crab, Callinectes sapidus

Eight cuticle protein transcripts from Callinectes sapidus were sequenced and their expression determined across the molt cycle in both calcifying and arthrodial cuticle hypodermis using quantitative PCR, Northern blots, and in situ hybridization. Four transcripts, designated CsAMP, are found only in non-calcifying arthrodial membrane hypodermis. They all code for a Rebers-Riddiford-1 motif, known to bind chitin. CsAMP9.3 is most likely an exocuticle constituent since it is expressed only during pre-molt. The other three arthrodial transcripts are present both before and after ecdysis. One of these, CsAMP16.3, codes for a RGD cell-attachment motif that could be involved in anchoring chitin-protein fibers to pore canals, cellular extensions of the hypodermis in the cuticle. The other four transcripts, designated CsCP, were found only in calcifying hypodermis. CsCP14.1 contains an RR-1 motif, which is more commonly found in non-calcifying cuticle proteins. CsCP6.1 is expressed post-molt and contains a partial RR motif, suggesting that it could bind to chitin in the endocuticle. The other two transcripts from calcifying hypodermis do not code for RR proteins, but both contain three copies of a different insect cuticle motif. One of these, CsCP19.0, is expressed only post-molt while the other, CsCP15.0, is present both before and after ecdysis.

Comprehensive sequence analysis of horseshoe crab cuticular proteins and their involvement in transglutaminase-dependent cross-linking

Arthropod cuticles play an important role as the first barrier against invading pathogens. We extensively determined the sequences of horseshoe crab cuticular proteins. Proteins extracted from a part of the ventral side of the cuticle were purified by chitin-affinity chromatography, and separated by two-dimensional SDS/PAGE. Proteins appearing on the gel were designated high molecular mass chitin-binding proteins, and these proteins were then grouped into classes based on their approximate isoelectric points and predominant amino acid compositions. Members of groups designated basic G, basic Y, and acidic S groups contained a so-called Rebers and Riddiford consensus found in arthropod cuticular proteins. Proteins designated acidic DE25 and DE29 each contained a Cys-rich domain with sequences similar to those of insect peritrophic matrix proteins and chitinases. In contrast, basic QH4 and QH10 contained no consensus sequences found in known chitin-binding proteins. Alternatively, a low molecular mass chitin-binding fraction was prepared by size exclusion chromatography, and 15 low molecular mass chitin-binding proteins, named P1 through P15, were isolated. With the exception of P9 and P15, all were found to be identical to known antimicrobial peptides. P9 consisted of a Kunitz-type chymotrypsin inhibitor sequence, and P15 contained a Cys-rich motif found in insulin-like growth factor-binding proteins. Interestingly, we observed transglutaminase-dependent polymerization of nearly all high molecular mass chitin-binding proteins, a finding suggests that transglutaminase-dependent cross-linking plays an important role in host defense in the arthropod cuticle, analogous to that observed in the epidermal cornified cell envelope in mammals.

Four differentially expressed cDNAs in Callinectes sapidus containing the Rebers–Riddiford consensus sequence

Decapod crustaceans such as Callinectes sapidus, the blue crab, provide unique opportunities to study proteins involved in biomineralization. Subsequent to each molt, the previously deposited soft cuticle is calcified while the postecdysial layers are simultaneously deposited and mineralized. Though the majority of the exoskeleton hardens, morphologically similar cuticle at the joints, called arthrodial membrane, remains flexible. It seems reasonable that hypodermal cells producing these cuticle types should be synthesizing proteins that regulate mineralization. Data presented here are consistent with this hypothesis, showing that transcripts coding for proteins containing the chitin-binding Rebers-Riddiford (RR) consensus sequence (Gx(8)Gx(7)YxAxExGYx(7)Px(2)P) are differentially expressed. Two RR-containing transcripts, CsAMP8.1 and CsAMP6.0, are found only in arthrodial membrane and are expressed uniformly both before and after ecdysis. They have high sequence homology with RR-containing proteins from uncalcified portions of the cuticle of Cancer pagurus, Penaeus japonicus, and Homarus americanus. The other two transcripts, CsCP8.5 and CsCP8.2, are expressed solely in premolt and in hypodermis depositing calcifying cuticle rather than arthrodial membrane. They have high sequence homology with calcification-associated peptides containing the RR sequence obtained from the calcified cuticle of Procambarus clarkii. This suggests possible involvement in the postmolt mineralization of the pre-ecdysial cuticle.

Expression of a serine proteinase homolog prophenoloxidase-activating factor from the blue crab, Callinectes sapidus

Tanning, or sclerotization, of crustacean cuticle provides initial reinforcement by cross linking cuticular proteins attached to the cuticle chitin-fiber matrix. This process is catalyzed in part by phenoloxidase, which is under the control of a serine protease activation cascade. The cDNA of a prophenoloxidase-activating factor (PPAF) was cloned and sequenced from the hypodermal tissue of the blue crab, Callinectes sapidus. It codes for a serine proteinase homolog containing a single clip domain. If it is involved in sclerotization, its transcription might be expected to be molt-cycle related. Expression patterns were determined by quantitative PCR and Northern blotting in hypodermis underlying both arthrodial and dorsal (calcifying) cuticles. Transcript levels in pre-molt RNA from both hypodermis types were high, suggesting that the PPAF produced may be incorporated into the pre-ecdysial cuticle layers and then activated at ecdysis to regulate tanning. After a decrease at ecdysis, a second increase in PPAF mRNA occurred at three to four hours post-molt in arthrodial membrane hypodermis but not dorsal hypodermis. This suggests that cuticle deposited after ecdysis may tan in the non-calcifying regions but may not tan where calcification occurs. The PPAF gene is also transcribed at low levels in the hemocytes of intermolt crabs, but not in the hepatopancreas.

Early pattern of calcification in the dorsal carapace of the blue crab,Callinectes sapidus

The pattern of calcium carbonate deposition was observed in the dorsal carapace of premolt (D2-D3) and early postmolt (0-48 h) blue crabs, Callinectes sapidus, using scanning (SEM) and transmission (TEM) electron microscopy. Samples of dorsal carapace for SEM were quick-frozen in liquid nitrogen, subsequently lyophilized, and viewed using secondary and backscattered electrons as well as X-ray maps of calcium. Pieces of lyophilized cuticle were also embedded in epoxy resin and subsequently sectioned and viewed with TEM and SEM. Fresh pieces of dorsal carapace for TEM were also fixed in 2.5% glutaraldehyde in phosphate buffer followed by postfixation in 1% OsO4 in cacodylate buffer. Calcium concentrations were determined using atomic absorption spectrophotometry and quantitative X-ray microanalysis. Calcium accumulation began in the cuticle at 3 h postmolt at the epicuticle/exocuticle boundary and at the distal and proximal margins of the interprismatic septa (IPS). The bidirectional calcification of the IPS continued until the two fronts met at 5-8 h postmolt. The roughly hexagonal walls of the IPS formed a honeycomb-like structure that resulted in a rigid cuticle. The walls of the canal containing sensory neurons also calcified at 3 h, thereby imparting rigidity to the structure and additional strength to the cuticle. Examination of thin sections of lyophilized cuticle and fixed cuticle revealed that the first mineral deposited is more soluble than calcite and is probably amorphous calcium carbonate. The amorphous calcium carbonate is transformed to calcite along a front that follows the original deposition and is probably controlled by a specialized matrix within the IPS. Since amorphous calcium carbonate is isotropic, it would also make the mineral in the exocuticle stronger by an equal distribution of mechanical stress.

Distribution of cuticular protein mRNAs in silk moth integument and imaginal discs

The distributions of mRNAs for two cuticular proteins of Hyalophora cecropia were examined with RT-PCR and in situ hybridization. For major regions of larval and pupal cuticle, there was a strong correspondence between the type of cuticle and the predominant cuticular protein message found. Epidermal cells underlying soft cuticle had mRNA for HCCP12, with a RR-1 consensus attributed to soft cuticle, while the epidermal cells associated with hard cuticle had predominantly mRNA for HCCP66, a protein with the RR-2 consensus attributed to hard cuticle. Both messages were found in all areas of the pupal fore- and hind-wings, with modest area-specific difference in concentration being much less than differences in the relative abundance of these cuticular proteins.mRNA for HCCP12 was present in imaginal discs of feeding larvae of H cecropia. Data from Bombyx mori available at SilkBase (http://www.ab.a.u-tokyo.ac.jp/silkbase/) revealed that imaginal discs from feeding larvae had abundant mRNA for RR-1 cuticular proteins, representing six distinct gene products. Only discs from spinning larvae had mRNAs that coded for RR-2 proteins arising from 10 distinct genes. Thus, lepidopteran wing imaginal discs can no longer be regarded as inactive in larval cuticle production.

Formation of the arthrodial membrane in the blue crab, Callinectes sapidus

In this study the pattern of arthrodial membrane deposition in Callinectes sapidus was determined by histological and ultrastructural examination of tissues from the carpus joint of the cheliped collected during premolt, ecdysis, postmolt, and intermolt. Apolysis in the arthrodial membrane occurs at stage D(0) and is synchronous with apolysis of the calcified cuticle. Epicuticle formation begins at early stage D(1) and is completed in late stage D(1). Procuticle deposition starts at D(2) and continues until ecdysis. Numerous cytoplasmic extensions occur throughout the lamellae. Component fibers of the arthrodial membrane are intimately associated with dense plaques on the apical membrane of the underlying hypodermal cells, suggesting a site for fiber polymerization. Deposition of the arthrodial membrane continues after ecdysis, with most of the cuticle thickening occurring during stage C. When stained with PAS and counterstained with hematoxylin, a difference can be discerned between preecdysial and postecdysial procuticle of the arthrodial membrane, a distinction not made in previous studies. The boundary between the arthrodial membrane and calcified cuticle is thicker than either of the two layers and the layers overlap rather than butting up against one another. This pattern suggests that underlying hypodermal cells have to produce multiple types of cuticle over the molt cycle. A summary of the various molting patterns in C. sapidus suggests that the control of these diverse events may prove to be complex.

Molecular cloning of a cDNA encoding a soluble protein in the coral exoskeleton

Organic substances were extracted from the calcified exoskeleton of the reef coral Galaxea fascicularis. In an SDS-PAGE analysis of the extract, a protein with an apparent molecular mass of 53 kDa was detected as well as two other weaker bands. A Ca2+ overlay analysis failed to find a Ca2+-binding protein in the extract. Periodic acid Schiff staining indicated that the 53 kDa protein was glycosylated. A cDNA containing the entire open reading frame for this protein was obtained. Analysis of the deduced protein sequence suggests that the protein, named galaxin, is synthesized as a precursor consisting of a signal peptide, a propeptide sequence, and a mature protein of 298 amino acids. Galaxin exhibits a novel amino acid sequence which is characterized by a tandem repeat structure. Galaxin transcripts were detected in the adult coral, but not in planktonic larvae.

Characterization and cDNA cloning of three major proteins from pharate pupal cuticle of Manduca sexta

Three proteins, MsCP20, MsCP27 and MsCP36, that are secreted in greatest quantity into the pharate pupal cuticle of Manduca sexta ( Hopkins et al., 2000) were purified and their amino acid sequences determined by mass spectrometry and Edman degradation. Although these proteins become sclerotized and insoluble in the pupal exoskeleton, their sequences contain features characteristic for proteins occurring in less sclerotized pliable cuticles, such as arthrodial membranes and soft larval cuticles. These proteins carry a secondary modification attached to a threonine residue, presumably an O-linked sugar moiety. cDNA clones of the genes for MsCP20, MsCP27 and MsCP36 were constructed from pharate pupal integument RNA. Close agreement was found between the amino acid sequences determined by Edman degradation and sequences deduced from the cDNA clones. The molecular masses determined by protein sequencing for MsCP20, MsCP27, and MsCP36 were 17713, 17448, and 29582 Da, respectively, in close agreement with the masses deduced from the corresponding cDNA clones (17711, 17410, and 29638 Da). Temporal expression analysis indicates that MsCP20 and MsCP36 transcripts are present at low levels early in the fifth larval stadium, followed by a large increase in abundance prior to pupal ecdysis. MsCP27 was not detected during development of the fifth larval instar, but its transcript, like those of MsCP20 and MsCP36, increased to a peak level just before pupal ecdysis. Only the MsCP36 transcript was detected in adults. These results support the hypothesis that these proteins are synthesized by the epidermis and are subsequently deposited into the cuticle during the larval-pupal transformation of M. sexta where they become sclerotized in the formation of pupal exocuticle.

Molecular cloning and characterization of a cDNA encoding a novel cuticle protein in the silkworm, Bombyx mori

We have cloned the full length of a novel cDNA named Bombyx mori cuticle protein that contains an AlaAlaProAla/Val-repeat (BMCPA) from a cDNA library of integument in the larval silkworm. Both a typical tandem repeat (A-A-P-A/V) for cuticle protein and a unique tandem repeat with Ser, Ala, Gly, Pro, Val, Tyr and Thr were observed in the predicted amino acid sequence of the cDNA encoding BMCPA. Approximately 80% of the amino acids in BMCPA were composed of Ser, Ala, Gly, Pro, Val and Tyr. Northern-hybridization analysis indicated that BMCPA mRNA is expressed only in the larval epidermis and that the expression pattern of the BMCPA gene in the developmental stage was observed mainly at the larval stage. We propose BMCPA may be a novel component of cuticle, and may play an important role in the integument of the larval silkworm.

Cuticular proteins from the horseshoe crab, Limulus polyphemus

Proteins were purified from the carapace cuticle of a juvenile horseshoe crab, Limulus polyphemus, and several of them were characterized by amino acid sequence determination. The proteins are small (7-16 kDa) and their isoelectric points range from 6.5 to 9.2. They have high contents of tyrosine, ranging from 13.5 to 35.4%. Some of the proteins show sequence similarity to cuticular proteins from other arthropod groups, with the most pronounced similarity to proteins from the cuticle of the spider Araneus diadematus. Two proteins show sequence similarity to a hexamerin storage protein from Blaberus discoidalis.

Characteristic properties of proteins from pre-ecdysial cuticle of larvae and pupae of the mealworm Tenebrio molitor

Proteins extracted from the cuticle of pharate larvae and pupae of the mealworm Tenebrio molitor are more soluble at low temperatures than at higher temperatures, a behaviour characteristic of hydrophobic proteins. When the temperature of an unfractionated cuticular extract is raised from 4 to 25 degrees C the solution becomes turbid, droplets of a heavy, protein-rich phase are formed, which gradually settles, leaving an upper protein-poor phase, indicating that the aggregation process is a coacervation. The aggregation of the dissolved cuticular proteins is influenced by changes in temperature, pH, and ionic strength. The process has been studied by measuring development of turbidity in unfractionated cuticular extracts and in solutions of three purified proteins from Tenebrio pharate larvae and pupae (TmLPCP-A1a, TmLPCP-E1a, and TmLPCP-G1a), while temperature, pH or ionic strength of the solutions were varied. Protein aggregation was also studied by determination of changes in fluorescence intensity, when the hydrophobicity probe, 8-anilinonaphthalenesulfonic acid (ANS) was added to solutions of the cuticular proteins. Only when the protein solutions had developed a measurable turbidity was an increase in ANS-fluorescence observed, indicating formation of tightly packed clusters of hydrophobic amino acid residues during aggregation. The temperature range for aggregation depends upon protein concentration: the higher the concentration the lower and more narrow is the temperature range within which aggregation occurs. The tendency for the individual cuticular proteins to aggregate is most pronounced near their isoelectric points, and most of the cuticular proteins have alkaline isoelectric points. The influence of salts on the tendency of the proteins to aggregate varies among the proteins and depends upon how close they are to their isoelectric point. A solution containing both protein TmLPCP-A1a and TmLPCP-E1a becomes more turbid and develops a more intense ANS-fluorescence when warmed from 10 to 30 degrees C than corresponding to the sum of measurements performed on separate solutions of the two proteins, indicating that the two proteins interact during aggregation. The Tenebrio larval/pupal cuticular proteins are characterized by an abundance of hydrophobic amino acid residues, and especially their contents of alanine and proline are high. The behaviour of the cuticular proteins in solution resembles that of another hydrophobic protein, tropoelastin, and it seems reasonable to suggest that similar interactions govern the folding and aggregation of the peptide chains in the two types of proteins. The proline and alanine rich chain segments in the pharate cuticular proteins are suggested to form a series of beta-turns and to fold into a relatively open structure at low temperatures, giving water access to the hydrophobic residues and making the proteins water soluble. At increased temperatures the structure of the ordered water layer surrounding the hydrophobic groups breaks down, and the peptide chains tend to collapse into a more closed structure and to interact more tightly with hydrophobic regions in neighbouring molecules. In dilute solutions in the test tube this results in aggregation and precipitation of the proteins; in intact, pharate cuticle at ambient temperatures the proteins will preferably be in an aggregated, easily dissociated state. Accordingly, small changes in intercuticular pH and ionic strength can produce pronounced changes in the mechanical properties of unsclerotized solid cuticle by interference with protein interactions, in agreement with reports that some cuticles undergo plasticization during and/or immediately after ecdysis.

Antibacterial activity in four marine crustacean decapods

A search for antibacterial activity in different body-parts of Pandalus borealis (northern shrimp), Pagurus bernhardus (hermit crab), Hyas araneus (spider crab) and Paralithodes camtschatica (king crab) was conducted. Dried samples were extracted with 60% (v/v) acetonitrile, containing 0.1% (v/v) trifluoroacetic acid, and further extracted and concentrated on C18 cartridges. Eluates from the solid phase extraction were tested for antibacterial, lysozyme and haemolytic activity. Antibacterial activity against Escherichia coli, Vibrio anguillarum, Corynebacterium glutamicum and Staphylococcus aureus was detected in extracts from several tissues in all species tested, but mainly in the haemolymph and haemocyte extracts. V. anguillarum and C. glutamicum were generally the most sensitive micro-organisms. In P. borealis and P. bernhardus most of the active fractions were not affected by proteinase K treatment, while in H. araneus and P. camtschatica most fractions were sensitive to proteinase K treatment, indicating antibacterial factors of proteinaceous nature. In P. bernhardus the active fractions were generally heat labile, whereas in H. araneus the activities were resistant to heat. Differences between active extracts regarding hydrophobicity and sensitivity for heat and proteinase K treatment indicate that several compounds are responsible for the antibacterial activities detected. Lysozyme-like activity could be detected in some fractions and haemolytic activity against human red blood cells could be detected in haemolymph/haemocyte and exoskeleton extracts from all species tested.

Glycoproteins from the cuticle of the Atlantic shore crab Carcinus maenas: I. Electrophoresis and Western-blot analysis by use of lectins

The protein and glycoprotein content of four different neutral or acidic solvent extracts (0.5 M KCl, 10% EDTA, 0.1 N HCl, or 2% acetic acid) from the mineralized exoskeleton of a decapod crustacean, the Atlantic shore crab Carcinus maenas, were characterized by quantitative analysis of proteins, SDS-PAGE analysis, and probing with lectins on blots. The lectins used were Conconavalin A, Jacalin, soybean agglutinin, Maackia amurensis agglutinin II, and Sambucus nigra agglutinin. The results show that many proteins can be obtained from the crab cuticle without strong denaturants in the extraction medium. Many of the extracted cuticle proteins appeared to be glycosylated, bearing O-linked oligosaccharides and N-linked mannose-rich glycans. N-acetyl-galactosamine and N-acetylneuraminic acids were revealed, for the first time, as terminal residues on N-linked mannose-rich structures of crab cuticle glycoproteins. Sialylated glycoproteins might thus be involved in organic-mineral interactions in the calcified crab exoskeleton. The amount and variety of glycoproteins extracted with the acidic solvents are obviously different from those extracted with neutral solvents. HCl proved to be the best of the tested extraction solvents and a valuable alternative to EDTA.

A conserved domain in arthropod cuticular proteins binds chitin

Many insect cuticular proteins include a 35-36 amino acid motif known as the R&R consensus. The extensive conservation of this region led to the suggestion that it functions to bind chitin. Provocatively, it has no sequence similarity to the well-known cysteine-containing chitin-binding domain found in chitinases and some peritrophic membrane proteins. Using fusion proteins expressed in E. coli, we show that an extended form of the R&R consensus from proteins of hard cuticles is necessary and sufficient for chitin binding. Recombinant AGCP2b, a putative cuticular protein from the mosquito Anopheles gambiae, was expressed in E. coli and the purified protein shown to bind to chitin beads. A stretch of 65 amino acids from AGCP2b, including the R&R consensus, conferred chitin binding to glutathione-S-transferase (GST). Directed mutagenesis of some conserved amino acids within this extended R&R consensus from hard cuticle eliminated chitin binding. Thus arthropods have two distinct classes of chitin binding proteins, those with the chitin-binding domain found in lectins, chitinases and peritrophic membranes (cysCBD) and those with the cuticular protein chitin-binding domain (non-cysCBD).

Purification and structural determination of a phosphorylated peptide with anti-calcification and chitin-binding activities in the exoskeleton of the crayfish, Procambarus clarkii

Organic matrices in calcified hard tissues have been considered to control calcification. A matrix peptide, designated CAP-1, was extracted and purified by anion-exchange and reverse-phase high performance liquid chromatographies from the exoskeleton of the crayfish, Procambarus clarkii. The amino acid sequence of CAP-1 was determined by mass spectral and sequence analyses of the intact peptide and its enzymatically digested peptides. CAP-1 consisted of 78 amino acid residues, including a phosphoserine residue, and was rich in acidic amino acid residues. CAP-1 had a Rebers-Riddiford consensus sequence, which is conserved in cuticle proteins from many arthropods. CAP-1 inhibited precipitation of calcium carbonate in an in vitro anticalcification assay dose-dependently, and completely inhibited it at 3 x 10(-7) M. CAP-1 also showed chitin-binding ability, indicating that this molecule was bifunctional and played an important role in formation of the exoskeleton.

The DD5 gene of the decapod crustacean Penaeus japonicus encodes a putative exoskeletal protein with a novel tandem repeat structure

A gene, named DD5, was identified in the penaeid prawn Penaeus japonicus and its cDNA cloned and sequenced. DD5 is expressed in the epidermal cells underlying the exoskeleton and the transcripts are detected specifically during the postmolt stage of the molt cycle. Sequence analysis of the conceptual protein product suggests that the DD5 protein is a component of the exoskeleton. The bulk of the protein consists of tandem repeats of a unit sequence of approximately 100 amino acids. The repeated sequences are highly homologous to one another and each of them includes a variant of the Rebers--Riddiford consensus sequence.

Studies on proteins in post-ecdysial nymphal cuticle of locust, Locusta migratoria, and cockroach, Blaberus craniifer

Proteins were extracted from the cuticle of mid-instar nymphs of locusts, Locusta migratoria, and cockroaches, Blaberus craniifer. Seven proteins were purified from the locust extract and five from the cockroach extract, and their amino acid sequences were determined. Polyacrylamide gel electrophoresis indicates that the proteins are present only in the post-ecdysially deposited layer of the nymphal cuticles. One of the locust and one of the cockroach nymphal proteins contain a 68-residue motif, the RR-2 sequence, which has been reported for several proteins from the solid cuticles of other insect species. Two of the cockroach proteins contain a 75-residue motif, which is also present in a protein from the larval/pupal cuticle of a beetle, Tenebrio molitor, and in proteins from the exoskeletons of a lobster, Homarus americanus, and a spider, Araneus diadematus. The motif contains a variant of the Rebers-Riddiford consensus sequence, and is called the RR-3 motif. One of the locust and three of the cockroach post-ecdysial proteins contain one or more copies of an 18-residue motif, previously reported in a protein from Bombyx mori pupal cuticle. The nymphal post-ecdysial proteins from both species have features in common with pre-ecdysial proteins (pharate proteins) in cuticles destined to be sclerotised; they show little similarity to the post-ecdysial cuticular proteins from adult locusts or to proteins from soft, pliable cuticles. Possible roles for post-ecdysial cuticular proteins are discussed in relation to the reported structures.

Molecular analysis of two genes, DD9A and B, which are expressed during the postmolt stage in the decapod crustacean Penaeus japonicus

In decapod crustaceans, deposition of calcium carbonate crystals (calcification) in the exoskeleton takes place during the postmolt phase of the molt cycle. In an attempt to identify proteins which regulate the calcification process, the differential display technique was used to identify genes which were specifically expressed in the integument during the postmolt stage in the penaeid prawn Penaeus japonicus. One of the genes thus identified, named DD9A, was expressed in the epithelial cells of the tail fan. DD9A encoded a putative precursor of a secreted protein of 113 amino acids which exhibited sequence similarities to a group of crustacean and insect cuticular proteins, suggesting that DD9A was a protein component of the exoskeleton. Another gene, DD9B, which was also transcribed specifically during the postmolt period was identified based on its sequence similarity to DD9A. Potential roles of the DD9A protein in the calcification of the exoskeleton will be discussed.