Evolution of the acute phase response: iron release by echinoderm (Asterias forbesi) coelomocytes, and cloning of an echinoderm ferritin molecule

Antarctic krill 454 pyrosequencing reveals chaperone and stress transcriptome

BACKGROUND

The Antarctic krill Euphausia superba is a keystone species in the Antarctic food chain. Not only is it a significant grazer of phytoplankton, but it is also a major food item for charismatic megafauna such as whales and seals and an important Southern Ocean fisheries crop. Ecological data suggest that this species is being affected by climate change and this will have considerable consequences for the balance of the Southern Ocean ecosystem. Hence, understanding how this organism functions is a priority area and will provide fundamental data for life history studies, energy budget calculations and food web models.

METHODOLOGY/PRINCIPAL FINDINGS

The assembly of the 454 transcriptome of E. superba resulted in 22,177 contigs with an average size of 492bp (ranging between 137 and 8515bp). In depth analysis of the data revealed an extensive catalogue of the cellular chaperone systems and the major antioxidant proteins. Full length sequences were characterised for the chaperones HSP70, HSP90 and the super-oxide dismutase antioxidants, with the discovery of potentially novel duplications of these genes. The sequence data contained 41,470 microsatellites and 17,776 Single Nucleotide Polymorphisms (SNPs/INDELS), providing a resource for population and also gene function studies.

CONCLUSIONS

This paper details the first 454 generated data for a pelagic Antarctic species or any pelagic crustacean globally. The classical "stress proteins", such as HSP70, HSP90, ferritin and GST were all highly expressed. These genes were shown to be over expressed in the transcriptomes of Antarctic notothenioid fish and hypothesized as adaptations to living in the cold, with the associated problems of decreased protein folding efficiency and increased vulnerability to damage by reactive oxygen species. Hence, these data will provide a major resource for future physiological work on krill, but in particular a suite of "stress" genes for studies understanding marine ectotherms' capacities to cope with environmental change.

Transcriptional up-regulation of a novel ferritin homolog in abalone Haliotis discus hannai Ino by dietary iron

A novel cDNA encoding ferritin (HdhNFT) was cloned from the hepatopancreas of abalone, Haliotis discus hannai Ino. The deduced protein contains 171 amino acid residues with a predicted molecular mass (MW) about 19.8 kDa and theoretical isoelectric point (pI) of 4.792. Amino acid alignment revealed that HdhNFT shared high similarity with other known ferritins. The HdhNFT contained a highly conserved motif for the ferroxidase center, which consists of seven residues of a typical vertebrate heavy-chain ferritin with a typical stem-loop structure. HdhNFT mRNA contains a 27 bp iron-responsive element (IRE) in the 5'-untranslated region. This IRE exhibited 82.14% similarity with abalone H. discus discus and 78.57% similarity with Pacific oyster Crassostrea gigas IREs. By real-time PCR assays, the mRNA transcripts of HdhNFT were found to be higher expressed in kidney, hepatopancreas, gill, mantle and muscle than in haemocytes and gonad. Moreover, mRNA expression levels of HdhNFT in the hepatopancreas and haemocytes were measured by real-time PCR in abalone fed with graded levels of dietary iron (29.2, 65.7, 1267.2 and 6264.7 mg/kg). Results showed that the expression of the HdhNFT mRNA increased with dietary iron contents. Furthermore, the maximum value of the HdhNFT mRNA was found in the treatment with 6264.7 mg/kg of dietary iron. These data indicated that dietary iron can up-regulate HdhNFT at transcriptional level in abalone.

Gene expression patterns of abalone, Haliotis tuberculata, during successive infections by the pathogen Vibrio harveyi

Since 1998, episodic mass mortality of the abalone Haliotistuberculata has been observed along the northern Brittany coast of France caused by a complex interaction among the host, pathogen and environmental factors. In the present study, abalone were submitted to two successive infections with the pathogen Vibrioharveyi under controlled conditions. During the first challenge, infection by V.harveyi resulted in 64% mortality of mature abalone. After a second infection of those surviving the first challenge, only 44% mortality was observed. Physiological variability in the host response appears to be a major determinant in susceptibility to V.harveyi. In order to isolate differentially expressed genes in H.tuberculata challenged with this bacterium, suppression subtractive hybridization (SSH) cDNA libraries were constructed from muscle of moribund abalone (susceptibles), surviving individuals (apparently resistant to the bacterium) and control (unexposed) animals. Of the 1152 clones sequenced, 218 different partial cDNA sequences were obtained and represented 69 known genes. Of these, 65 were identified for the first time in H.tuberculata. Using real-time PCR, a time-course study was conducted on 19 of the genes identified by SSH. A majority of differentially expressed transcripts were down-regulated in susceptible individuals as compared to their resistant counterparts. Bacterial challenge of abalone resulted in the up-regulation of three transcripts (encoding ferritin, heat shock protein HSP84 and fatty acid binding protein FABP) in those that survived exposure to V.harveyi. This study has identified potential candidates for further investigation into the functional basis of resistance and susceptibility to summer vibriosis outbreaks in abalone.

Identification of immune genes of the Agamaki clam (Sinonovacula constricta) by sequencing and bioinformatic analysis of ESTs

The Agamaki clam (Sinonovacula constricta) is an economically important shellfish in Asia. However, genomic research on this species is still in its infancy, and genomic resources are largely unavailable. The objective of this study was to generate expressed sequence tags (ESTs) from a normalized liver complementary DNA library and to identify genes that function in immune defense. A total of 5,296 ESTs were sequenced, from which 540 contigs and 3,473 singletons were identified. BLAST homology analysis indicated that only 20.7% of these ESTs were homologues of known genes while the remaining 79.3% appeared to be novel sequences. Based on sequence similarities, 43 putative immune genes were identified that encode proteases and protease inhibitors, adhesive proteins, stress proteins, lysosomal enzymes, and signal transduction regulators. Our study thus provides both a large collection of novel transcripts and a detailed annotation of immune genes for an important bivalve species.

Iron in obesity. An ancient micronutrient for a modern disease

Iron is a necessary constituent of several macromolecules involved in cell metabolism, but, at the same time, it could be a potentially dangerous element. For this reason iron balance must be finely regulated. At present, obesity has been recognized as a worldwide public health problem. Excess body fat is associated with increased all-cause mortality and increased risk for several medical morbidities. Many studies have shown that obesity might increase the risk of iron deficiency but, at the same time, obese subjects exhibit high serum ferritin levels. Recent studies seem to indicate that obesity is associated with iron deficiency although the aetiology appears to be multifactorial and includes (i) A decrease in iron food intake; (ii) An impairment of intestinal iron uptake and iron release from stores because of an overexpression of hepcidin and (iii) Inadequate iron bioavailability because of inflammation. In addition, abnormal ferritin concentrations can be explained by chronic inflammation rather than by iron overload. The aim of the present article is to review current knowledge of iron and obesity.

Two novel secreted ferritins involved in immune defense of Chinese mitten crab Eriocheir sinensis

As a principal extracellular iron storage molecule, secreted ferritin plays an important role in the iron-withholding strategy of innate immunity. In this study, two novel secreted ferritins were identified from Chinese mitten crab Eriocheir sinensis (designated as EsFer-1 and EsFer-2) by rapid amplification of cDNA ends (RACE) approaches and expressed sequence tag (EST) analysis. The full-length cDNAs of EsFer-1 and EsFer-2 were of 1278 and 1595 bp, respectively, both containing a putative iron response element (IRE) in their 5' UTRs and multiple A + U-destabilizing elements (TATT or ATTTA) in their 3' UTRs. The ORFs of these two crab ferritin cDNAs were of 639 and 663 bp, respectively, encoding two peptides of 212 and 220 amino acid residues each with a signal peptide and typical structures of ferritins such as four long alpha-helices, one short alpha-helix and an L-loop. EsFer-2 exhibited higher similarity with the H-ferritins from both invertebrates and vertebrates, while EsFer-1 was closer matched to L-ferritins. The eight amino acid residues identified as metal binding sites in vertebrate H-ferritins were conserved in EsFer-2 (Glu53, Tyr60, Glu87, Glu88, His91, Glu146, Glu177 and Gln178), but none of them was observed in EsFer-1. By fluorescent quantitative real-time PCR, mRNA transcripts of EsFer-1 and EsFer-2 were mainly detected in muscle, hepatopancreas and gill, and also marginally detectable in gonad, heart and hemocytes. After the crabs were challenged by bacteria Listonella anguillarum, the transcriptional levels of both EsFer-1 and EsFer-2 in hemocytes were up-regulated twice. In the first up-regulation, the mRNA relative expression levels of both EsFer-1 and EsFer-2 reached peak at 3 h post-challenge, while in the second up-regulation, they did not reach the highest point within the experiment duration. After the fungi Pichia pastoris GS115 challenge, there was only one transcriptional level peak of both the two ferritins, appearing at 6 h post-challenge. These results suggest that secreted EsFer-1 and EsFer-2 are crucial proteins in the iron-withholding defense system, and play important roles in the innate immune responses in crabs.

Wolbachia interferes with ferritin expression and iron metabolism in insects

Wolbachia is an intracellular bacterium generally described as being a facultative reproductive parasite. However, Wolbachia is necessary for oogenesis completion in the wasp Asobara tabida. This dependence has evolved recently as a result of interference with apoptosis during oogenesis. Through comparative transcriptomics between symbiotic and aposymbiotic individuals, we observed a differential expression of ferritin, which forms a complex involved in iron storage. Iron is an essential element that is in limited supply in the cell. However, it is also a highly toxic precursor of Reactive Oxygen Species (ROS). Ferritin has also been shown to play a key role in host-pathogen interactions. Measuring ferritin by quantitative RT-PCR, we confirmed that ferritin was upregulated in aposymbiotic compared to symbiotic individuals. Manipulating the iron content in the diet, we showed that iron overload markedly affected wasp development and induced apoptotic processes during oogenesis in A. tabida, suggesting that the regulation of iron homeostasis may also be related to the obligate dependence of the wasp. Finally, we demonstrated that iron metabolism is influenced by the presence of Wolbachia not only in the obligate mutualism with A. tabida, but also in facultative parasitism involving Drosophila simulans and in Aedes aegypti cells. In these latter cases, the expression of Wolbachia bacterioferritin was also increased in the presence of iron, showing that Wolbachia responds to the concentration of iron. Our results indicate that Wolbachia may generally interfere with iron metabolism. The high affinity of Wolbachia for iron might be due to physiological requirement of the bacterium, but it could also be what allows the symbiont to persist in the organism by reducing the labile iron concentration, thus protecting the cell from oxidative stress and apoptosis. These findings also reinforce the idea that pathogenic, parasitic and mutualistic intracellular bacteria all use the same molecular mechanisms to survive and replicate within host cells. By impacting the general physiology of the host, the presence of a symbiont may select for host compensatory mechanisms, which extends the possible consequences of persistent endosymbiont on the evolution of their hosts.

Identification and expression of differentially expressed genes in the hard clam, Mercenaria mercenaria, in response to quahog parasite unknown (QPX)

Background

The hard clam, Mercenaria mercenaria, has been affected by severe mortality episodes associated with the protistan parasite QPX (Quahog Parasite Unknown) for several years. Despite the commercial importance of hard clams in the United States, molecular bases of defense mechanisms in M. mercenaria, especially during QPX infection, remain unknown.

Results

Our study used suppression subtractive hybridization (SSH), as well as the construction of cDNA libraries from hemocytes to identify genes related to the defense of the hard clam against its parasite. Hard clams were experimentally infected with QPX and SSH was performed on mRNA samples extracted from mantle and gill tissues at different times post-challenge. A total of 298 clones from SSH libraries and 1352 clones from cDNA libraries were sequenced. Among these sequences, homologies with genes involved in different physiological processes related to signal transduction, stress response, immunity and protein synthesis were identified. Quantitative PCR revealed significant changes in the expression of several of these genes in response to QPX challenge and demonstrated significant correlations in terms of levels of gene expression between intermediates of signalling pathways and humoral defense factors, such as big defensin and lysozyme.

Conclusion

Results of this study allowed the detection of modifications caused by QPX at the transcriptional level providing insight into clam immune response to the infection. These investigations permitted the identification of candidate genes and pathways for further analyses of biological bases of clam resistance to QPX allowing for a better understanding of bivalve immunity in general.

Identification of genes involved in immune response, microsatellite, and SNP markers from expressed sequence tags generated from hemocytes of freshwater pearl mussel (Hyriopsis cumingii)

Triangle sail mussel (Hyriopsis cumingii) is the most important mussel species commercially exploited for freshwater pearl production in China. However, its genome research is still at the infantry. Genomic resources for this species are largely not available. The objectives of this study was to generate expressed sequence tags from a hemocyte cDNA library, to identify genes involved in defense mechanisms, and to identify polymorphic markers from the expressed sequence tag (EST) resources for genetic analysis. A total of 5,290 ESTs were sequenced, obtaining 481 contigs and 1,165 singletons. BLAST similarity analysis indicated almost half (46.5%) of these ESTs were homologs of known genes while 53.5% were transcripts of unknown identities. Based on sequence similarities, 50 genes were identified as putative genes involved in immune and defense functions such as hemocyte immune process, stress proteins, adhesive proteins, proteases and protease regulators, antimicrobial peptides, lysosomal enzymes, cell apoptosis, and cell cycle proteins. A total of 201 microsatellites were identified from these ESTs, with 31 having sufficient flanking sequences for primer design. Polymerase chain reaction amplification was successful for 18 primer pairs and 14 of them were polymorphic. A total of 987 putative single nucleotide polymorphisms were identified including 204 transitions, 611 transversions, and 172 indels; 12 of them were involved in nine genes of defense mechanisms. These resources provide the material basis for future marker validation and genetic linkage and quantitative trait loci analysis in the freshwater pearl mussel.

Response of the symbiotic cnidarian Anthopleura elegantissima transcriptome to temperature and UV increase

Elevated temperature and solar radiation, including ultraviolet radiation, are now recognized as the primary environmental stresses that lead to mass cnidarian bleaching. This study takes a functional genomics approach to identifying genes that change expression soon after exposure to these stressors in the temperate sea anemone Anthopleura elegantissima that harbors Symbiodinium, the same genus of symbionts found in reef-building corals. Symbiotic anemones were subjected to elevated temperature or UV over a 24 h period. cDNA from these animals was hybridized to a 10,000-feature cDNA microarray of A. elegantissima. Overall 2.7% of the 10,000 features were found to be differentially expressed as a function of temperature or UV stress. Of the 86 features sequenced, 45% displayed significant homology to sequences in GenBank. There are 27 features that were differentially expressed in both stress conditions. Gene ontology analysis placed the differentially expressed genes in a wide range of categories including cytoskeleton organization and biogenesis, protein biosynthesis, cell proliferation, apoptosis and transport. This suggests that the early stress response to elevated temperature and UV involves essentially all aspects of host cellular regulation and machinery and that downstream cnidarian bleaching is a complex cellular response in host tissues.

Comparative ORESTES-sampling of transcriptomes of immune-challenged Biomphalaria glabrata snails

The snail Biomphalaria glabrata (Gastropoda, Mollusca) is an important intermediate host for the human parasite Schistosoma mansoni (Digenea, Trematoda). Anti-pathogen responses of B. glabrata were studied towards a better understanding of snail immunity and host-parasite compatibility. Open reading frame ESTs (ORESTES) were sampled from different transcriptomes of M line strain B. glabrata, 12h post-challenge with Escherichia coli (Gram-negative), Micrococcus luteus (Gram-positive) bacteria or compatible S. mansoni, and controls. The resulting 3123 ORESTES represented 2129 unique sequences (373 clusters, 1756 singletons). Of these, 175 (8.1%) were putative defense factors, including lectins, antimicrobial peptides and components of various immune-effector systems. Comparison of biological processes (GO-terms) within different transcriptomes indicated that B. glabrata increased oxygen transport and metal binding in reaction to all challenges. Comprehensive comparisons of transcriptomes revealed that responses of B. glabrata against bacteria were similar to each other and differed from the ineffective response to S. mansoni. Furthermore, the response to S. mansoni infection was less comprehensive than that to bacteria. Many novel (unknown) sequences were recovered in association with particular challenges. B. glabrata possesses multi-faceted, potent immune defenses. This agrees with the notion that S. mansoni is capable of immune-evasion and prevents effective host defense responses in order to survive in B. glabrata. Future analysis of the numerous unknown sequences recovered from challenged snails may reveal novel immune factors and provide increased understanding of immunity of B. glabrata in relation to parasite-host compatibility.

Coral life history and symbiosis: functional genomic resources for two reef building Caribbean corals, Acropora palmata and Montastraea faveolata

Background

Scleractinian corals are the foundation of reef ecosystems in tropical marine environments. Their great success is due to interactions with endosymbiotic dinoflagellates (Symbiodinium spp.), with which they are obligately symbiotic. To develop a foundation for studying coral biology and coral symbiosis, we have constructed a set of cDNA libraries and generated and annotated ESTs from two species of corals, Acropora palmata and Montastraea faveolata.

Results

We generated 14,588 (Ap) and 3,854 (Mf) high quality ESTs from five life history/symbiosis stages (spawned eggs, early-stage planula larvae, late-stage planula larvae either infected with symbionts or uninfected, and adult coral). The ESTs assembled into a set of primarily stage-specific clusters, producing 4,980 (Ap), and 1,732 (Mf) unigenes. The egg stage library, relative to the other developmental stages, was enriched in genes functioning in cell division and proliferation, transcription, signal transduction, and regulation of protein function. Fifteen unigenes were identified as candidate symbiosis-related genes as they were expressed in all libraries constructed from the symbiotic stages and were absent from all of the non symbiotic stages. These include several DNA interacting proteins, and one highly expressed unigene (containing 17 cDNAs) with no significant protein-coding region. A significant number of unigenes (25) encode potential pattern recognition receptors (lectins, scavenger receptors, and others), as well as genes that may function in signaling pathways involved in innate immune responses (toll-like signaling, NFkB p105, and MAP kinases). Comparison between the A. palmata and an A. millepora EST dataset identified ferritin as a highly expressed gene in both datasets that appears to be undergoing adaptive evolution. Five unigenes appear to be restricted to the Scleractinia, as they had no homology to any sequences in the nr databases nor to the non-scleractinian cnidarians Nematostella vectensis and Hydra magnipapillata.

Conclusion

Partial sequencing of 5 cDNA libraries each for A. palmata and M. faveolata has produced a rich set of candidate genes (4,980 genes from A. palmata, and 1,732 genes from M. faveolata) that we can use as a starting point for examining the life history and symbiosis of these two species, as well as to further expand the dataset of cnidarian genes for comparative genomics and evolutionary studies.

Analysis of differentially expressed genes in response to bacterial stimulation in hemocytes of the carpet-shell clam Ruditapes decussatus: Identification of new antimicrobial peptides

Suppression subtractive hybridization was used to identify differentially expressed genes in hemocytes from carpet-shell clam Ruditapes decussatus stimulated with a mixture of dead bacterial strains. Putative function could be assigned to 100 of the 253 sequenced cDNAs. Based on sequence homologies, 3.16% of the total identified genes were possibly related to immune functions. Clam myticin isoforms 1, 2 and 3, and clam mytilin, with similarity with myticins and mytilins previously reported on Mytilus galloprovincialis were identified and characterized for the first time in clams. The analysis of their expression levels by quantitative PCR showed that they were induced by bacterial challenge. The results obtained in this work could be the first step leading to the understanding of molecular mechanisms by which these economically important marine bivalves respond to pathogens.

Differential expression of immune-related genes and transposable elements in black tiger shrimp (Penaeus monodon) exposed to a range of environmental stressors

The health of aquatic species is dependent on interactions between the environment, pathogens and the host. Under intensive shrimp aquaculture, environmental conditions can degrade, causing significant stress to the cultured organisms. To investigate the effect of environmental stress on shrimp hemocyte gene expression profiles, we applied suppression subtractive hybridization (SSH) in juvenile Penaeus monodon exposed to hyperthermal, hypoxic or hyposmotic conditions. Random sequencing of 258 clones from the SSH revealed 176 distinct sequences of which 58 shared high similarity to sequences in the public databases. The three most common groups of identifiable unique sequences in the SSH libraries were the POL region of non-LTR retrotransposons (31%), genes with immune or potential immune functions (30%), and genes involved in protein synthesis and processing (18%). Stress-regulated differential expression was further verified by quantitative qRT-PCR, with seven out of eight randomly selected genes showing qRT-PCR profiles that conformed to the patterns predicted by SSH. Hence this work provides a list of genes which appear to be up- or down-regulated in response to stress, providing a basis for studying the genetic response of shrimp to environmental stress.

Two ferritin subunits from disk abalone (Haliotis discus discus): cloning, characterization and expression analysis

Ferritin plays a key role in cellular iron metabolism, which includes iron storage and detoxification. From disk abalone, Haliotis discus discus, the cDNA that encodes the two ferritin subunits abalone ferritin subunit 1 (Abf1) and abalone ferritin subunit 2 (Abf2) were cloned. The complete cDNA coding sequences for Abf1 and Abf2 contained 621 and 549 bp, encoding for 207 and 183 amino acid residues, respectively. The H. discus discus Abf2 subunit contained a highly conserved motif for the ferroxidase center, which consists of seven residues of a typical vertebrate heavy-chain ferritin with a typical stem-loop structure. Abf2 mRNA contains a 27 bp iron-responsive element (IRE) in the 5'UTR position. This IRE exhibited 96% similarity with pearl and Pacific oyster and 67% similarity with human H type IREs. However, the Abf1 subunit had neither ferroxidase center residues nor the IRE motif sequence; instead, it contained iron-binding region signature 2 (IBRS) residues. Recombinant Abf1 and Abf2 proteins were purified and the respective sizes were about 24 and 21 kDa. Abf1 and Abf2 exhibited iron-chelating activity 44.2% and 22.0%, respectively, at protein concentration of 6 microg/ml. Analysis of tissue-specific expression by RT-PCR revealed that Abf1 and Abf2 ferritin mRNAs were expressed in various abalone tissues, such as gill, mantle, gonad, foot and digestive tract in a wide distribution profile, but Abf2 expression was more prominent than Abf1.

Evolution of the iron-responsive element

An RNA hairpin structure referred to as the iron-responsive element (IRE) and iron regulatory proteins (IRPs) are key players in the control of iron metabolism in animal cells. They regulate translation initiation or mRNA stability, and the IRE is found in a variety of mRNAs, such as those encoding ferritin, transferrin receptor (Tfr), erythroid aminolevulinic acid synthase (eALAS), mitochondrial aconitase (mACO), ferroportin, and divalent metal transporter 1 (DMT1). We have studied the evolution of the IRE by considering all mRNAs previously known to be associated with this structure and by computationally examining its occurrence in a large variety of eukaryotic organisms. More than 100 novel sequences together with approximately 50 IREs that were previously reported resulted in a comprehensive view of the phylogenetic distribution of this element. A comparison of the different mRNAs shows that the IREs of eALAS and mACO are found in chordates, those of ferroportin and Tfr1 are found in vertebrates, and the IRE of DMT1 is confined to mammals. In contrast, the IRE of ferritin occurs in a majority of metazoa including lower metazoa such as sponges and Nematostella (sea anemone). These findings suggest that the ferritin IRE represents the ancestral version of this type of translational control and that during the evolution of higher animals the IRE structure was adopted by other genes. On the basis of primary sequence comparison between different organisms, we suggest that some of these IREs developed by "convergent evolution" through stepwise changes in sequence, rather than by recombination events.

Identification of genes involved in interactions between Biomphalaria glabrata and Schistosoma mansoni by suppression subtractive hybridization

Biomphalaria glabrata is an intermediate snail host for Schistosoma mansoni, a medically important schistosome. In order to identify transcripts involved in snail-schistosome interactions, subtractive cDNA libraries were prepared, using suppression subtractive hybridization (SSH) between a parasite-exposed schistosome-resistant and a susceptible strain of B. glabrata, and also between schistosome-exposed and unexposed snails from the resistant snail line. Separate libraries were made from both haemocytes and the haemopoietic organ. Subtraction was performed in both directions enriching for cDNAs differentially expressed between parasite-exposed resistant and susceptible samples and up or down-regulated in the resistant line after challenge. The resulting eight libraries were screened and eight genes, differentially expressed between the haemocytes of resistant and susceptible snail strains, were identified and confirmed with reverse transcriptase PCR, including two transcripts expected to be involved in the stress response mechanism for regulating the damaging oxidative burst pathways involved in cytotoxic killing of the parasite: the iron-storage and immunoregulatory molecule, ferritin, and HtrA2, a serine protease involved in the cellular stress response. Transcripts with elevated levels in the resistant strain, had the same expression patterns in the subtracted libraries and unsubtracted controls; higher levels in exposed resistant snails compared to susceptible ones and down-regulated in exposed compared with unexposed resistant snails. Differential expression of two of the transcripts with no known function from the susceptible strain, was independently confirmed in a repeat exposure experiment.

Cloning, expression and identification of ferritin from Chinese shrimp, Fenneropenaeus chinensis

Ferritin, the iron storage protein, plays a key role in iron metabolism. A cDNA encoding ferritin (FcFer) was cloned from hepatopancreas of Chinese shrimp, Fenneropenaeus chinensis. The predicted protein contains 170 amino acid residues with a predicted molecular weight (MW) about 19, 422.89 Da and theoretical isoelectric point (PI) of 4.73. Amino acid alignment of FcFer revealed 97% homology with Litopenaeus vannamei ferritin. Results of the RT-PCR showed that the expression of FcFer mRNA was up-regulated after shrimp was challenged with either white spot syndrome virus (WSSV) or heavy metal ions (Zn2+ and Cu2+) in the laboratory. A fusion protein containing FcFer was produced and the purified recombinant protein exhibited similar function of iron uptake in vitro. The result of in-gel digestion and identification using LC-ESI-MS showed that two peptide fragments (-DDVALPGFAK- and -LLEDEYLEEQVDSIKK-) of the recombinant protein were identical to the corresponding sequence of L. vannamei ferritin. The recombinant FcFer protein will be proved useful for study on the structure and function of ferritin in F. chinensis.

Iron-withholding strategy in innate immunity

The knowledge of how organisms fight infections has largely been built upon the ability of host innate immune molecules to recognize microbial determinants. Although of overwhelming importance, pathogen recognition is but only one of the facets of innate immunity. A primitive yet effective antimicrobial mechanism which operates by depriving microbial organisms of their nutrients has been brought into the forefront of innate immunity once again. Such a tactic is commonly referred to as the iron-withholding strategy of innate immunity. In this review, we introduce various vertebrate iron-binding proteins and their invertebrate homologues, so as to impress upon readers an obscured arm of innate immune defense. An excellent comprehension of the mechanics of innate immunity paves the way for the possibility that novel antimicrobial therapeutics may emerge one day to overcome the prevalent antibiotic resistance in bacteria.

HSP70 gene expression in Mytilus galloprovincialis hemocytes is triggered by moderate heat shock and Vibrio anguillarum, but not by V. splendidus or Micrococcus lysodeikticus

Complete sequence of HSP70 cDNA from the mussel, Mytilus galloprovincialis was established before quantifying its expression following moderate heat shock or injection of heat-killed bacteria. HSP70 cDNA is comprised of 2378 bp including one ORF of 654 aa, with a predicted 70 bp 5'-UTR and a 343 bp 3'-UTR (GenBank, 18 Jan 05, AY861684). Alignment identity ranged from 89% for Crassostrea ariakensis to 72% for C. virginica. Curiously, HSP70 gene and cDNA sequences from M. galloprovincialis, deposited later (03 and 27 May), show only 73% identity with the present sequence. Meanwhile, characteristic motifs of the HSP70 family were located in conserved positions. Expression of HSP70 gene was quantified on circulating hemocyte mRNA using Q-PCR after RT using random hexaprimers. Housekeeping gene was 28S rRNA. Four stresses were applied: heat shock that consisted of immersing mussels for 90 min at 30 degrees C and returning them to 20 degrees C sea water, one injection of heat-killed Gram-negative bacteria, Vibrio splendidus LGP32, one injection of heat-killed Gram-negative bacteria Vibrio anguillarum, one injection of heat-killed Gram-positive bacteria Micrococcus lysodeikticus. We found no significant modification of 28S rRNA gene expression. Significant increase of 5.2 +/- 0.4 fold the ratio HSP70/28S rRNA was observed 6 h after heat shock and was maximum at 15 h (6.1 +/- 1.1), and still significant after 24 h (1.7 +/- 0.03). Similarly, injecting V. anguillarum resulted in a significant increase of 2.7 +/- 0.1 after 12 h. Expression was maximum after 48 h (5.2 +/- 0.05) and returned to baseline after 72 h. In contrast, injecting V. splendidus or M. lysodeikticus failed to significantly modulate HSP70 gene expression at least during the first 3 days post-injection. Consequently, mussel hemocytes appeared to discriminate between pathogenic and non-pathogenic Vibrios, as well as between Gram-negative and Gram-positive bacteria.

Monitoring chemical and physical stress using sea urchin immune cells

Coelomocytes are the cells freely circulating in the body fluid contained in echinoderm coelom and constitute the defence system, which, in response to injuries, host invasion, and adverse conditions, is capable of chemotaxis, phagocytosis, and production of cytotoxic metabolites. Red and colourless amoebocytes, petaloid and philopodial phagocytes, and vibratile cells are the cell types that, in different proportions, constitute the mixed coelomocyte cell population found in sea urchins. Advances in cellular and molecular biology have made it possible to identify a number of specific proteins expressed in coelomocytes under resting conditions or when activated by experimentally induced stress. Only recently, coelomocytes have been used for pollution studies with the aim of introducing a new biosensor for detection of stress at both cellular and molecular levels, as sentinel of sea health. In this chapter, we briefly review the important features of these valuable cells and describe studies on their use in the laboratory and in the field for the assessment of chemical and physical pollution of the sea.

Crassostrea gigas ferritin: cDNA sequence analysis for two heavy chain type subunits and protein purification

Ferritin has been shown as being the principal iron storage in the majority of living organisms. In marine species, ferritin is also involved in high-level accumulation of (210)Po. As part of our work on the investigation of these radionuclides' concentration in natural environment, ferritin was searched at the gene and protein level. Ferritin was purified from the visceral mass of the oyster Crassostrea gigas by ion-exchange chromatography and HPLC. SDS-PAGE revealed one band of 20 kDa. An Expressed Sequence Tag (EST) library was screened and led to the identification of two complementary DNA (cDNA) involved in ferritin subunit expression. The complete coding sequences and the untranslated regions (UTRs) of the two genes were obtained and a 5' Rapid Amplification of cDNA Ends (RACE) was used to obtain the two iron-responsive elements (IREs) with the predicted stem-loop structures usually present in the 5'-UTR of ferritin mRNA. Sequence alignment in amino acid of the two new cDNA showed an identity with Pinctada fucata (85.4-88.3%), Lymnaea stagnalis (79.3-82.2%) and Helix pomatia (79.1-79.1%). The residues responsible for the ferroxidase center, conserved in all vertebrate H-ferritins, are present in the two oyster ferritin subunits. Oyster ferritins do not present the special characteristics of other invertebrate ferritins like insect ferritins but have some functional similarities with the vertebrate H chains ferritin.

Stress and transcriptional regulation of tick ferritin HC

We previously identified a partial Dermacentor variabilis cDNA encoding ferritin HC (HC) subunit homolog (DVFER) that was differentially upregulated in Rickettsia montanensis infected ticks (Mulenga et al., 2003a). We have used rapid amplification of cDNA ends to clone full-length DVFER cDNA and its apparent ortholog from the wood tick, D. andersoni (DAFER), both of which show high sequence similarity to vertebrate than insect ferritin. Both DVFER and DAFER contain the stem-loop structure of a putative iron responsive element in the 5' untranslated region (nucleotide positions, 16-42) and the feroxidase centre loop typical for vertebrate ferritin HC subunits. Quantitative Western and Northern blotting analyses of protein and RNA from unfed and partially fed whole tick as well as dissected tick tissues demonstrated that DVFER is constitutively and ubiquitously expressed. Based on densitometric analysis of detected protein and mRNA bands, DVFER is predominantly expressed in the midgut, and to a lesser extent in the salivary glands, ovary and fatbody. Sham treatment (mechanical injury) and Escherichia coli challenge of D. variabilis ticks stimulated statistically significant (approximately 1.5- and approximately 3.0-fold, respectively) increases in DVFER mRNA abundance over time point matched naive control ticks. These data suggest that DVFER mRNA is nonspecifically up regulated in response to mechanical injury or bacterial infection induced stress.

A novel ferritin subunit involved in shell formation from the pearl oyster (Pinctada fucata)

Iron is one of the most important minor elements in the shell of bivalves. This study was designed to investigate the involvement of ferritin, the principal protein for iron storage, in shell formation. A novel ferritin cDNA from the pearl oyster (Pinctada fucata) was isolated and characterized. The ferritin cDNA encodes a 206 amino acid polypeptide, which shares high similarity with snail soma ferritin and the H-chains of mammalian ferritins. Oyster ferritin mRNA shows the highest level of expression in the mantle, the organ for shell formation. In situ hybridization analysis revealed that oyster ferritin mRNA is expressed at the highest level at the mantle fold, a region essential for metal accumulation and contributes to metal incorporation into the shell. Taken together, these results suggest that ferritin is involved in shell formation by iron storage. The identification and characterization of oyster ferritin also helps to further understand the structural and functional properties of molluscan ferritins.

Lipopolysaccharides induce intestinal serum amyloid A expression in the sea cucumber Holothuria glaberrima

We have previously characterized the first invertebrate homolog of serum amyloid A (SAA) proteins in the sea cucumber Holothuria glaberrima, where its expression is associated with intestinal regeneration, suggesting a possible involvement of SAA proteins in intestinal morphogenesis. Here we show that bacterial lipopolysaccharides (LPS) trigger a coelomocyte-mediated immune response in H. glaberrima, inducing an approximately threefold increase in coelomocyte phagocytic activity. Furthermore, LPS induces an approximately fourfold increase in SAA mRNA levels in non-regenerating intestines. These results show that in H. glaberrima, LPS act as an immune activator and that SAA expression can be modulated by immune-associated processes.

Immune gene discovery by expressed sequence tags generated from hemocytes of the bacteria-challenged oyster, Crassostrea gigas

An expressed sequence tag program was undertaken to isolate genes involved in defense mechanisms of the Pacific oyster, Crassostrea gigas. Putative function could be assigned to 54% of the 1142 sequenced cDNAs. We built a public database where all EST information are accessible through numerous search profiles (http://www.ifremer.fr/GigasBase). Based on sequence similarities we identified 20 genes that may be implicated in immune function. We investigated the expression of four of these genes during bacterial challenge of oysters. Three of them were induced in response to challenge lending support to their involvement in oyster immunity. Moreover, four other genes were highly homologous to components of the NF-kappa B signaling pathway which is involved in innate immune response in Drosophila and mammals. Altogether, our results open a new way to investigate the immune response in mollusks.