Mantle Tissue Research Articles

Advances in pre-operative techniques for pearl production in the lions-paw scallop Nodipecten subnodosus: Relaxation and mantle excision

Relaxation and excision of mantle tissue from live lions-paw scallops can assist in the optimum development of pre-operative techniques for pearl production in this species. To determine the feasibility of relaxing the scallop, five scallops were exposed to each of nine relaxant treatments previously used for pearl seeding operations. Relaxation and suitable conditions for seeding operations were obtained in scallops exposed to 30gL−1 magnesium chloride and to 1mLL−1 2-phenoxyethanol. To determine the healing capacity and ability to sustain tissue excision, a section of mantle tissue was removed from 15 relaxed scallops. Survival 30days after excision was 87% and all scallops showed signs of regeneration. Microscopic examination confirmed the elongation of the mantle epithelia and growth of new connective tissue. This relaxation technique is an important step in developing basic technology for pearl production, as previously accomplished with other species. This is an important tool that will improve successful production of lions-paw scallop cultured pearls. This can add significant value to the scallop-cultivating industry and the pearl industry.

Impacts of seawater acidification on mantle gene expression patterns of the Baltic Sea blue mussel: implications for shell formation and energy metabolism

Marine organisms have to cope with increasing CO2 partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pCO2 treatments (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm) on mantle gene expression patterns in the blue mussel Mytilus edulis from the Baltic Sea. Based on the M. edulis mantle tissue transcriptome, the expression of several genes involved in metabolism, calcification and stress responses was assessed in the outer (marginal and pallial zone) and the inner mantle tissues (central zone) using quantitative real-time PCR. The expression of genes involved in energy and protein metabolism (F-ATPase, hexokinase and elongation factor alpha) was strongly affected by acclimation to moderately elevated CO2 partial pressures. Expression of a chitinase, potentially important for the calcification process, was strongly depressed (maximum ninefold), correlating with a linear decrease in shell growth observed in the experimental animals. Interestingly, shell matrix protein candidate genes were less affected by CO2 in both tissues. A compensatory process toward enhanced shell protection is indicated by a massive increase in the expression of tyrosinase, a gene involved in periostracum formation (maximum 220-fold). Using correlation matrices and a force-directed layout network graph, we were able to uncover possible underlying regulatory networks and the connections between different pathways, thereby providing a molecular basis of observed changes in animal physiology in response to ocean acidification.

Changes in oxidative stress parameters in relation to age, growth and reproduction in the short-lived catarina scallop Argopecten ventricosus reared in its natural environment

Increase in oxidative damage and decrease in cellular maintenance is often associated with aging, but, in marine ectotherms, both processes are also strongly influenced by somatic growth, maturation and reproduction. In this study, we used a single cohort of the short-lived catarina scallop Argopecten ventricosus, to investigate the effects of somatic growth, reproduction and aging on oxidative damage parameters (protein carbonyls, TBARS and lipofuscin) and cellular maintenance mechanisms (antioxidant activity and apoptosis) in scallops, caged in their natural environment. The concentrations of protein carbonyls and TBARS increased steeply during the early period of fast growth and during reproduction in one-year-old scallops. However, oxidative damage was transient, and apoptotic cell death played a pivotal role in eliminating damage in gill, mantle and muscle tissues of young scallops. Animals were able to reproduce again in the second year, but the reduced intensity of apoptosis impaired subsequent removal of damaged cells. In late survivors low antioxidant capacity and apoptotic activity together with a fast accumulation of the age pigment lipofuscin was observed. Rates of oxygen consumption and oxidative stress markers were strongly dependent on somatic growth and reproductive state but not on temperature. Compared to longer-lived bivalves, A. ventricosus seems more susceptible to oxidative stress with higher tissue-specific protein carbonyl levels and fast accumulation of lipofuscin in animals surviving the second spawning. Superoxide dismutase activity and apoptotic cell death intensity were however higher in this short-lived scallop than in longer-lived bivalves. The life strategy of this short-lived and intensely predated scallop supports rapid somatic growth and fitness as well as early maturation at young age at the cost of fast cellular degradation in second year scallops.

Selection of Target Mussel Tissue for Application of Cellular Energy Allocation as a Physiological Biomarker in Native MusselsMytilus galloprovincialis(Lamarck, 1819)

Three selected mussel tissues (digestive gland, mantle, and gills) were studied to determine which was the most suitable for the potential use of the cellular energy allocation (CEA) methodology in indigenous mussels Mytilus galloprovincialis. In addition, the applicability of CEA in the assessment of natural stress caused by salinity fluctuations in stratified estuary was tested in selected tissues. It was important to identify the mussel gender to reliably assess the changes in organism energy budget. CEA value was calculated as a ratio between available energy (Ea) and energy consumption (Ec). Mantle tissue was under the strongest influence of the differences in protein and lipid content between male and female mussels, and therefore reflected physiological changes in the organism itself, rather than those caused by natural environmental stress. CEA in gills had lower values than in mantle and digestive gland, and was similar at two selected sampling sites, so the changes in CEA caused by natural stress could not be detected in the gill tissue. Greater Ec in mussels from the estuarine site than from the coastal site was detected only in the digestive gland tissue, and can probably be attributed to the energetically costly maintenance of osmotic balance. Last, using digestive gland tissue in CEA analysis demonstrated a clear difference between coastal and estuarine sampling sites, providing the measure of the natural stress posed by variations in salinity.

The Microstructure of the Cultured Freshwater Pearl

Pearls are composite materials of calcium carbonate polymorphs (calcite and aragonite) and organic macromolecules (polysaccharides and proteins) which contain genes and transcription factors that direct the formation of calcite and aragonite polygonal tiles, including their shape, size, and geometrical accommodation. These biologically derived instructions are transmitted from donor mussel shell mantle tissue by inserting seed grafts into freshwater production mussels. In this paper the internal and external freshwater pearl structure for the cultured triangle mussel Hyriopsis cumingii is examined by light optical microscopy, scanning electron microscopy, and x-ray diffraction. Pearl interior crystal structure evolves as mainly concentric calcite tile layers from the seed sac, with mixtures of aragonite polygonal (hexagonal-like) tiles. Within about 0.8–1 mm from the ideal (curved) pearl surface, the aragonite tiles form as continuous, overlapping layers 300–400 nm thick, with interlamellar organic material.

Metabolomic analysis of sex specific metabolites in gonads of the mussel, Mytilus edulis

Marine mussels have been used as sentinel organisms to monitor exposure to a variety of chemical contaminants, including endocrine disrupting chemicals, in the aquatic environment. Although they are an important species for use in ecotoxicology investigations, information on their reproductive physiology and biochemistry is fragmentary. Mass spectrometry-based profiling techniques are increasingly being used to study how the metabolome of an organism changes as a result of tissue differentiation, disease or in response to environmental stressors. In this study, ultraperformance liquid chromatography–time-of-flight-mass spectrometry (UPLC–TOFMS) was used to investigate sex specific differences in the mussel metabolome in order to further investigate the reproductive physiology of this species. Using this method, a comparison of female and male mantle tissues containing mature gonad, revealed significant differences in glycerophosphatidylcholine (PC) and lysophosphatidylcholine (LPC) metabolites. A number of other unidentified metabolites, including those putatively identified as conjugated sterols, were also differentially expressed between male and female mantle/gonadal tissue.

Study of chemical properties and evaluation of collagen in mantle, epidermal connective tissue and tentacle of Indian Squid, Loligo duvauceli Orbigny.

The chemical composition and evaluation of Indian squid (Loligo duvauceli) mantle, epidermal connective tissue and tentacle is investigated in this current study. It is observed that squid mantle contains 22.2% total protein; 63.5% of the total protein is myofibrillar protein. The unique property of squid myofibrillar protein is its water solubility. Squid mantle contains 12.0% total collagen. Epidermal connective tissue has highest amounts of total collagen (17.8%). SDS-PAGE of total collagen identified high molecular weight α-, β- and γ- sub-chains. Amino acid profile analysis indicates that mantle and tentacle contain essential amino acids. Arginine forms a major portion of mantle collagen (272.5g/100g N). Isoleucine, glutamic acid and lysine are other amino acids that are found in significantly high amounts in the mantle. Sulphur containing cystine is deficit in mantle collagen. Papain digest of mantle and epidermal connective tissue is rich in uronic acid, while papain digest, collagenase digest and urea digest of epidermal connective tissue has significant amounts of sialic acid (25.2, 33.2 and 99.8μmol /100g, respectively). PAS staining of papain digest, collagenase digest and urea digest also identify the association of hexoses with low molecular weight collagen fragments. Histochemical sectioning also emphasized the localized distribution of collagen in epidermal and dermal region and very sparse fibres traverse the myotome bundles.

Changes of total carotenoid and lipid content in scallop tissues of Chlamys nobilis (Bivalve: Pectinidae) during gonad maturation

The noble scallop Chlamys nobilis is an important edible marine bivalve, which has been cultured in the Southern Sea of China since 1980s. Our previous study showed that the total carotenoid content (TCC) in this species was related to body tissue, shell color, and gender, which was the highest in the ovary of the scallops with orange shell and adductor muscle. In the present study, TCC and total lipid content (TLC) in three tissues of adductor muscle, mantle and gonad at different days were determined and compared using four groups of scallops including gonad mature male (MM), gonad mature female (MF), gonad gametocytogenesis male (GcM), and gonad gametocytogenesis female (GcF) and correlations between TCC and TLC for different tissues were analyzed in order to find out how they change during gonad maturation and whether they have correlation with each other in this species. All employed scallops were from the same family produced in autumn 2008 and had the same orange shell, mantle and adductor muscle with higher TCC. The present results showed that both TCC and TLC changed during maturation, but changing trend was different among tissues. In adductor muscle, TCC increased for MM and MF, but decreased for GcM and GcF; TLC had no significant change for all groups. In mantle, TCC significantly changed only in the GcF, which decreased from 327.18μgg−1 to 257.96μgg−1; TLC strikingly changed only in the MF, which increased from 5.33% to 6.77%. In gonad, TCC decreased in MM and increased in other groups; TLC increased in all groups. Particularly interesting and important, a significantly positive correlation (P<0.05) between TCC and TLC was detected in the gonad tissues during maturation, which was also for the first time reported in marine mollusks. The present results also firstly demonstrated that both carotenoid and lipid not only were significantly accumulated in gonad, but also might be transferred from other tissues during maturation in mollusks, particularly in the female.

A goose-type lysozyme gene in Japanese scallop (Mizuhopecten yessoensis): cDNA cloning, mRNA expression and promoter sequence analysis

Lysozyme is an important component of the immune response against bacteria that is characterized by its ability to break down bacterial cell-walls. We constructed a high-quality cDNA library from mantle tissue of adult Japanese scallop (Mizuhopecten yessoensis). The EST which is high homology with g-type lysozyme genes of other species was found in the cDNA library. In the present study, the complete express sequence of g-type lysozyme genes from Japanese scallop (designated as MyLysoG) was directly obtained by PCR. The complete sequence of MyLysoG cDNA consisted of a 5' untranslated region (UTR) of 25 bp, an open reading frame (ORF) of 606 bp, and a 3' UTR of 100 bp with one polyadenylation signal (AATAAA). The deduced amino acids of MyLysoG were 201 amino acids with a putative signal peptide of 18 amino acid residues. It shared the sequence similarity and the common structure features with the g-type lysozyme from other species. Quantitative reverse trancriptase real-time PCR (qRT-PCR) assay demonstrated that mRNA transcripts of g-type lysozyme could be detected in various tissues of unchallenged scallop, and the highest expression of MyLysoG was detected in hepatopancreas tissue. The temporal expression of MyLysoG in hemolymph after Vibrio anguillarum challenge was up-regulated and reached the maximum level at 3h post stimulation, and then dropped back to the original level even lower than the control group. Furthermore, a 978 bp of 5'-flanking sequence of MyLysoG was identified by genome walking, and several potential transcription factor binding sites (TFBS) were detected in the putative promoter region. One part of the MyLysoG promoter region contains nine sites of SNPs and three sites of insert-deletion (indel) polymorphisms, and these mutations were found organize into two haplotypes. The two haplotypes were associated with different TFBS. The haplotypes could be selected to analyze the transcriptional-level control of scallop g-type lysozyme gene and the scallop immune system.

Mantle Display and Glochidia Release Behaviors of Five Quadruline Freshwater Mussel Species (Bivalvia: Unionidae)

Abstract: Diverse strategies have evolved in freshwater mussels to promote the transfer of their parasitic larvae to host fish. Among these, modification of the mantle as a host attracting lure has been well-documented in the Tribe Lampsilini, but only recently reported in the Tribe Quadrulini. Here we describe mantle modifications and glochidia release behaviors in five quadruline species, including members of the Quadrula quadrula (Rafinesque, 1820), Q. pustulosa (Lea, 1831), and Q. metanevra (Rafinesque, 1820) species groups. Displays were motionless and consisted of inflated mantle tissue surrounding the excurrent aperture. Gross display morphology was largely variable among species: Q. fragosa (Conrad, 1835) and Tritogonia verrucosa (Rafinesque, 1820) had relatively large, uniquely shaped displays; Cyclonaias tuberculata (Rafinesque, 1820) and Q. pustulosa had smaller, stomate-shaped displays; and Q. metanevra had a diminutive, polyp-like display. Cyclonaias tuberculata exhibited a bimodal host infec...

Transcriptome analysis of biomineralisation-related genes within the pearl sac: Host and donor oyster contribution

Cultured pearl production is a complex biological process involving the implantation of a mantle graft from a donor pearl oyster along with a bead nucleus into the gonad of a second recipient host oyster. Therefore, pearl production potentially involves the genetic co-operation of two oyster genomes. Whilst many genes in the mantle tissue have been identified and linked to shell biomineralisation in pearl oysters, few studies have determined which of these biomineralisation genes are expressed in the pearl sac and potentially linked to pearl biomineralisation processes. It is also uncertain whether the host or donor oyster is primarily responsible for the expression of biomineralisation genes governing pearl formation, with only two shell matrix proteins previously identified as being expressed by the donor oyster in the pearl sac. To further our understanding of pearl formation, the pearl sac transcriptome of Pinctada maxima and Pinctada margaritifera was each sequenced to an equivalent 5× genome coverage with putative molluscan biomineralisation-related genes identified. Furthermore, the host and donor contribution of these expressed genes within the pearl sac were quantified using a novel approach whereby two pearl oyster species harbouring unique genomes, P. maxima or P. margaritifera, were used to produce xenografted pearl sacs.A total of 19 putative mollusc biomineralisation genes were identified and found to be expressed in the pearl sacs of P. maxima and P. margaritifera. From this list of expressed genes, species-diagnostic single nucleotide polymorphisms (SNP) were identified within seven of these genes; Linkine, N66, Perline, N44, MSI60, Calreticulin and PfCHS1. Based on the presence/absence of species diagnostic gene transcripts within xenografted pearl sacs, all seven genes were found to be expressed by the species used as the donor oyster. In one individual we also found that the host was expressing Linkine. These results convincingly show for the first time that the donor mantle tissue is primarily responsible for the expression of biomineralisation genes in the pearl sac.

The chemical composition and meat yield of sexually mature cuttlefish (Sepia officinalis)

The objective of the present study was to determine the chemical composition and meat yield for both sexes of adult cuttlefish, Sepia officinalis, in the Mersin Bay, East Mediterranean. The results of meat yield showed that meat yield of adult male cuttlefish were higher than those of the female. The levels of protein ranged from 22.15% to 22.20%, lipid from 0.86% to 1.01%, and water from 74.97% to 75.30%, total mineral substance (TMS) from 1.68% to 1.69% for mantle of female and male cuttlefish. Moreover, there were not variations in protein, lipid, water and TMS content of mantle tissues of both adult females and males (p>0.05). The levels of saturated fatty acids (SFA) ranged from 29.49% to 29.88%, monounsaturated fatty acids (MUFAs) from 10.97% to 11.40%, and polyunsaturated fatty acids (PUFAs) from 52.27% to 53.42% for both of the sexes. In the present study, the major fatty acids found in S. officinalis were palmitic acid (C16:0), stearic acid (C18:0), eicosapentaenoic acid (EPA, C20:5 n-3) and docosahexaenoic acid (DHA, C22:6 n-3). Statistically, there were no significant differences in DHA concentrations in mantle tissue of male and female cuttlefish (p>0.05). Besides, EPA concentrations in mantle of female cuttlefish were higher than those of the male (p0.05). Cu content of female cuttlefish was sig-nificantly higher (p

Molecular characteristics and expression of calmodulin cDNA from the freshwater pearl mussel, Hyriopsis schlegelii

Calmodulin (CaM) is a multifunctional intracellular calcium ion receptor protein that participates in a range of cellular processes, including calcium metabolism in mussels. To investigate the role of CaM in freshwater mollusk shell calcium metabolism, the full-length CaM cDNA was isolated from the freshwater pearl mussel, Hyriopsis schlegelii (referred to as hsCaM) using SMART RACE technology. The full-length hsCaM was 855 bp in size, containing a 70-bp 5'-untranslated sequence, a 447-bp open reading frame, a 309-bp 3'-untranslated sequence, and a 26-nucleotide long poly(A) tail. The hsCaM mRNA expression in different mussel tissues was examined using real-time PCR. The hsCaM mRNA was found to be ubiquitously expressed, but far more abundant in the gill, foot, and mantle than in the posterior adductor muscle. Real-time PCR was also used to determine hsCaM mRNA expression levels in mantle tissues of H. schlegelii at different ages. No significant differences between one-, two-, and three-year-old mussels were detected, but expression increased in four-year-old mussels and then decreased in five-year-old mussels. CaM appears to be involved in calcium regulation of the mantle in four-year-old mussels, which may secrete more mother of pearl during pearl culture.

An Improved Method of DNA Extraction from the Shell of the Pacific Oyster, Crassostrea gigas

We earlier developed a method to extract DNA from in vivo-sampled mantle tissue of the bivalve Pacific oyster (Crassostrea gigas) for molecular marker-assisted selection (MAS) in breeding. However, mortality was too high when using this method. In the current study, a more efficient and safer method of extracting DNA from the oyster shell was developed, based on the improved phenol-chloroform DNA extraction method. Both nuclear DNA and mitochondrial DNA were successfully extracted from the oyster shell, and mortality was 0%. These results illustrate the safety of extracting DNA from the bivalve shell. In addition, because DNA is a cellular component, the results provide molecular evidence that cells are likely involved in shell formation.

Proteomic Strategy for Identifying Mollusc Shell Proteins Using Mild Chemical Degradation and Trypsin Digestion of Insoluble Organic Shell Matrix: A Pilot Study on Haliotis tuberculata

A successful strategy for the identification of shell proteins is based on proteomic analyses where soluble and insoluble fractions isolated from organic shell matrix are digested with trypsin with the aim of generating peptides, which are used to identify novel shell proteins contained in databases. However, using trypsin as a sole degradative agent is limited by the enzyme's cleavage specificity and is dependent upon the occurrence of lysine and arginine in the shell protein sequence. To bypass this limitation, we investigated the ability of trifluoroacetic acid (TFA), a low-specificity chemical degradative agent, to generate clusters of analyzable peptides from organic shell matrix, suitable for database annotation. Acetic acid-insoluble fractions from Haliotis tuberculata shell were processed by trypsin followed by TFA digestion. The hydrolysates were used to annotate an expressed sequence tag library constructed from the mantle tissue of Haliotis asinina, a tropical abalone species. The characterization of sequences with repeat motifs featured in some of the shell matrix proteins benefited from TFA-induced serial cutting, which can result in peptide ladder series. Using the degradative specificities of TFA and trypsin, we were able to identify five novel shell proteins. This pilot study indicates that a mild chemical digestion of organic shell matrix combined with trypsin generates peptides suitable for proteomic analysis for better characterization of mollusc shell matrix proteins.

Subchronic effects of environment-like cadmium levels on the bivalve Anodonta anatina (Linnaeus 1758): I. Bioaccumulation, distribution and effects on calcium metabolism

Cadmium (Cd) bioaccumulation, tissue distribution, and its effects on Ca levels in the freshwater bivalve Anodonta anatina were examined. Mussels were exposed for 35 days to algae- and water-borne 111Cd at an environment-like concentration and were allowed to depurate for posterior 120 days. Body fluids and tissue samples were taken during both phases to determine total Cd, the 114Cd:111Cd isotope ratio, the electrolytes Ca and Mg, and the essential trace metal zinc (Zn). Bioaccumulation and distribution of Cd and its effects on Ca levels were tissue-specific and time-dependent. During exposure, newly incorporated 111Cd increased in all body compartments, with highest levels in the kidney. During depuration, newly incorporated and background Cd both decreased slowly in the digestive gland and others while in the kidney it increased further, indicating mobilization from other body compartments and deposition in this organ. Following the uptake of Cd, Ca concentrations increased in body fluids within a few hours while it decreased in the digestive gland, mantle and other tissues; in the gills and kidney it remained largely unchanged. The derangement of Ca homeostasis, to some extent also of Mg and Zn, appears to be a major component of subchronic Cd toxicity in A. anatina.

Spatial analysis of biomineralization associated gene expression from the mantle organ of the pearl oyster Pinctada maxima

BackgroundBiomineralization is a process encompassing all mineral containing tissues produced within an organism. One of the most dynamic examples of this process is the formation of the mollusk shell, comprising a variety of crystal phases and microstructures. The organic component incorporated within the shell is said to dictate this architecture. However general understanding of how this process is achieved remains ambiguous. The mantle is a conserved organ involved in shell formation throughout molluscs. Specifically the mantle is thought to be responsible for secreting the protein component of the shell. This study employs molecular approaches to determine the spatial expression of genes within the mantle tissue to further the elucidation of the shell biomineralization.ResultsA microarray platform was custom generated (PmaxArray 1.0) from the pearl oyster Pinctada maxima. PmaxArray 1.0 consists of 4992 expressed sequence tags (ESTs) originating from mantle tissue. This microarray was used to analyze the spatial expression of ESTs throughout the mantle organ. The mantle was dissected into five discrete regions and analyzed for differential gene expression with PmaxArray 1.0. Over 2000 ESTs were determined to be differentially expressed among the tissue sections, identifying five major expression regions. In situ hybridization validated and further localized the expression for a subset of these ESTs. Comparative sequence similarity analysis of these ESTs revealed a number of the transcripts were novel while others showed significant sequence similarities to previously characterized shell related genes.ConclusionsThis investigation has mapped the spatial distribution for over 2000 ESTs present on PmaxArray 1.0 with reference to specific locations of the mantle. Expression profile clusters have indicated at least five unique functioning zones in the mantle. Three of these zones are likely involved in shell related activities including formation of nacre, periostracum and calcitic prismatic microstructure. A number of novel and known transcripts have been identified from these clusters. The development of PmaxArray 1.0, and the spatial map of its ESTs expression in the mantle has begun characterizing the molecular mechanisms linking the organics and inorganics of the molluscan shell.

Cloning and localization of MCdef, a defensin from Manila clams (Ruditapes philippinarum)

A defensin-like peptide was previously detected in hemocytes of Manila clams (Ruditapes philippinarum). In the current study, we cloned and characterized this defensin, designated MCdef. Cloning produced a full-length gene sequence of 201 bp predicted to encode a 66-amino-acid precursor protein maturing to a 44-amino-acid residue. Amino acid sequence analysis showed that MCdef is similar to defensins from marine mollusks and ticks. Phylogenetic analysis suggested that MCdef is closely related to defensins from Mytilus galloprovincialis (Mediterranean mussel) and Crassostrea gigas (Pacific cupped oyster). The three-dimensional structure of MCdef was modeled using the solution structure of C. gigas defensin as a template. With the exception of three variable loop areas, the modeled structure of MCdef was identical to that of C. gigas defensin. MCdef antiserum was raised against a synthetic MCdef peptide and verified by Western blotting using recombinant MCdef. RT-PCR analysis demonstrated high levels of MCdef mRNA in hemocytes and adductor, foot, gill, mantle, palp, and siphon tissues of Vibrio tapetis-infected Manila clams, whereas in V. tapetis-uninfected Manila clams, the level of MCdef mRNA was low in adductor, palp, and siphon tissues and even lower in the other tested tissues. Immunohistochemical analysis revealed high MCdef expression was detected in the gill, the mantle, and the digestive tubules of the diverticulum of V. tapetis-infected Manila clams. Minimum inhibitory concentration (MIC) of the purified rMCdef was determined. MCdef showed highest activity against Streptococcus iniae and Staphylococcus aureus.

Size-dependent photosynthetic performance in the giant clam Tridacna maxima, a mixotrophic marine bivalve

Giant clams form a symbiosis with photosynthetic algae of the genus Symbiodinium that reside in clam mantle tissue. The allometry of symbiont photosynthetic performance was investigated as a mechanism for the increasing percentage of giant clam carbon respiratory requirements provided by symbionts as clam size increases. Chlorophyll fluorescence measurements of symbionts of the giant clam Tridacna maxima were measured during experiments conducted in September of 2009 using specimens 0.5–200 g tissue wet weight (3–25 cm long), collected from waters around southern Taiwan (N 21°36′, E 120°47′) from July to August of 2009. Light-dependent decreases in effective quantum yield (∆F/Fm′) calculated as the noontime maximum excitation pressure over PSII (Qm), relative electron transport rates (rETR), and dark-adapted maximum quantum yield (Fv/Fm) all varied as a quadratic function of clam size. Both Qm and rETR increased as clam size increased up to ~10–50 g then decreased as clam size increased. Fv/Fm decreased as clam size increased up to ~5–50 g then increased as clam size increased. Chlorophyll fluorescence measurements of rETR were positively correlated with gross primary production measured during chamber incubations. Overall, symbionts of mid-sized clams ~5–50 g exhibited the highest light-dependent decreases in effective photosynthetic efficiencies, the highest relative electron transport rates, and the lowest maximum photosynthetic efficiencies, and symbiont photosynthetic performance is allometric with respect to host clam size.

Molecular cloning and expression analysis of a selenium-independent glutathione peroxidase identified from Manila clam Venerupis philippinarum

Glutathione peroxidase (GPx) is a key enzyme of cellular detoxification systems that defend cells against reactive oxygen species. It can be divided into selenium-dependent GPx (Se-GPx) and selenium-independent GPx (non-Se-GPx) subfamilies. In this study, the full-length cDNA of a non-Se-GPx was identified from Venerupis philippinarum (denoted as VpGPx) using EST analysis and RACE approaches. The full-length cDNA of VpGPx encoded a polypeptide of 226 amino acids with the predicted molecular mass of 25.41 similar to kDa. Phylogenetic analysis indicated that VpGPx had higher evolutional conservation to invertebrate than vertebrate counterparts and should be a new member of the GPx protein family. Spatial expression analysis found that VpGPx transcript was most abundantly expressed in hepatopancreas, gills and haemocytes, and weakly expressed in the tissues of mantle. After Vibrio anguillarum challenge, the expression of VpGPx transcript in overall haemocyte population was down-regulated in the first 6 similar to h, and increased to the peak at 48 similar to h. As time progressed, the expression level dropped to 0.5-fold of the control level at 96 similar to h. All these results indicated that VpGPx was perhaps involved in the immune response against microbe infection and might be contributed to the clearance of bacterial pathogens.