Shell Matrix Research Articles

Characterization of the Pearl Oyster (Pinctada martensii) Mantle Transcriptome Unravels Biomineralization Genes

Pearl oyster, Pinctada martensii, is a marine bivalve species widely distributed in tropic and subtropic marine coasts. Mantle is the special tissue of P. martensii that secretes biomineralization proteins inducing shell deposition as well as iridescent nacre both in the inner shell and artificial nucleus. The pearl oyster is very efficient for artificial pearl production and is therefore an ideal organism for studies into the processes of biomineralization. However, deficiency of transcriptome information limits the insight into biomineralization mechanisms and pearl formation. In this study, we sequenced and characterized the P. martensii mantle transcriptome using 454 pyrosequencing. A total of 25,723 unique transcripts were assembled from 220,824 quality reads, followed by annotation and Gene Ontology classification analysis. A total of 146 unique transcript segments homologous to 49 reference biomineralization genes were identified, including calcineurin-binding protein, amorphous calcium carbonate binding protein 1, calmodulin, calponin-like protein, carbonic anhydrase 1, glycine-rich shell matrix protein, lysine-rich matrix protein, mantle gene or protein, nacrein, pearlin, PIF, regucalcin, and shematrin. The sequence data enabled the identification of 10,285 potential single nucleotide polymorphism loci and 7,836 putative indels, providing a resource for molecular biomarker, population genetics, and functional genomic studies. A large number of candidate genes for biomineralization were identified, considerably enriching resources for the study of shell formation. These sequence data will notably advance biomineralization and transcriptome study in pearl oyster and other Pinctada species.

A Comparative Study of the Shell Matrix Protein Aspein in Pterioid Bivalves

Aspein is one of the unusually acidic shell matrix proteins originally identified from the pearl oyster Pinctada fucata. Aspein is thought to play important roles in the shell formation, especially in calcite precipitation in the prismatic layer. In this study, we identified Aspein homologs from three closely related pterioid species: Pinctada maxima, Isognomon perna, and Pteria penguin. Our immunoassays showed that they are present in the calcitic prismatic layer but not in the aragonitic nacreous layer of the shells. Sequence comparison showed that the Ser-Glu-Pro and the Asp-Ala repeat motifs are conserved among these Aspein homologs, indicating that they are functionally important. All Aspein homologs examined share the Asp-rich D-domain, suggesting that this domain might have a very important function in calcium carbonate formation. However, sequence analyses showed a significantly high level of variation in the arrangement of Asp in the D-domain even among very closely related species. This observation suggests that specific arrangements of Asp are not required for the functions of the D-domain.

Dermatopontin, a shell matrix protein gene from pearl oyster Pinctada martensii, participates in nacre formation

Dermatopontin (DPT) is identified as a major component of the shell matrix protein. However, its exact function in the shell formation remains obscure. In this study, we described the characteristic and function of DPT gene from Pinctada martensii. DPT cDNA was 797bp long, containing an open reading fragment (ORF) of 537bp encoding a polypeptide of 178 amino acids with an estimated molecular mass of 21.4kDa and theoretical isoelectric point of 5.97. The 5′ untranslated region (UTR) was 11bp and the 3′UTR was 249 with 18bp poly (A) tail. In the peptide, there was a signal sequence, six potential phosphorylation sites, one glycosylation site and eight cysteine residues. Moreover, a sequence motif (D-R-X-W/F/Y-X-F/Y/I/L/M-X1–2-C) was contained and repeated itself three times in the entire sequence. DPT mRNA was constitutively expressed in all studied tissues with the most abundant mRNA in the mantle, which was nacre formation-related tissue. After decreasing DPT expression using RNA interference (RNAi) technology in the mantle, the nacreous layer showed a disordered growth; whereas the prismatic layer of the shells has no significant changes. These results suggested that DPT obtained in this study was a constitutive matrix protein and participated in nacre formation in P. martensii.

Effects of multiple washing on cotton fabrics containing berberine microcapsules with anti-Staphylococcus aureus activity

The therapeutic efficiency and topical performance of drug-containing microcapsules varied when the drugs existed in an internal oil phase or an internal aqueous phase within the wall shell or wall matrix of microcapsules. In this study, chitosan-based (oil-in-water) and agar–gelatin-based (water-in-oil) microencapsulation systems containing berberine were applied to cotton fabrics to provide an anti-Staphylococcus aureus activity for textile materials. The berberine microcapsule-treated cotton samples were subjected to various washing cycles and their surface morphology, chemical compositions and antibacterial property were investigated after washing. The SEM images and Fourier transform infrared analysis showed that the amount of microcapsules on cotton samples decreased gradually with an increase in washing cycles. After 20 washing cycles, the cotton fabrics with agar–gelatin (water-in-oil) microcapsules containing berberine still exhibited the anti-S. aureus activity. However, the chitosan-based (oil-in-water) system did not show any growth inhibition towards S. aureus but only in the contact areas.

Identification of Two Carbonic Anhydrases in the Mantle of the European Abalone Haliotis tuberculata (Gastropoda, Haliotidae): Phylogenetic Implications

Carbonic anhydrases (CAs) represent a diversified family of metalloenzymes that reversibly catalyze the hydration of carbon dioxide. They are involved in a wide range of functions, among which is the formation of CaCO(3) skeletons in metazoans. In the shell-forming mantle tissues of mollusks, the location of the CA catalytic activity is elusive and gives birth to contradicting views. In the present paper, using the European abalone Haliotis tuberculata, a key model gastropod in biomineralization studies, we identified and characterized two CAs (htCA1 and htCA2) that are specific of the shell-forming mantle tissue. We analyzed them in a phylogenetic context. Combining various approaches, including proteomics, activity tests, and in silico analyses, we showed that htCA1 is secreted but is not incorporated in the organic matrix of the abalone shell and that htCA2 is transmembrane. Together with previous studies dealing with molluskan CAs, our findings suggest two possible modes of action for shell mineralization: the first mode applies to, for example, the bivalves Unio pictorum and Pinctada fucata, and involves a true CA activity in their shell matrix; the second mode corresponds to, for example, the European abalone, and does not include CA activity in the shell matrix. Our work provides new insight on the diversity of the extracellular macromolecular tools used for shell biomineralization study in mollusks.

Facile synthesis of silver immobilized-poly(methyl methacrylate)/polyethyleneimine core–shell particle composites

A facile route to synthesize silver-embedded-poly(methyl methacrylate)/polyethyleneimine (PMMA/PEI-Ag) core–shell particle composites was illustrated in this present work. PMMA/PEI core–shell particle templates were first prepared by a surfactant-free emulsion polymerization. PEI on the templates' surface was further used to complex and reduce Ag+ ions (from silver nitrate solution) to silver nanoparticles (AgNPs) at ambient temperature, resulting in the PMMA/PEI-Ag particle composites. The formation of AgNPs was affected by the pHs of the reaction medium. The pH of reaction medium at 6.5 was optimal for the formation of PMMA/PEI-Ag with good colloidal stability, which was confirmed by size and size distribution, FTIR spectroscopy, UV–vis spectroscopy and X-ray diffraction. Moreover, the amount of AgNO3 solution (4.17–12.50g) was found to affect the formation of AgNPs. Transmission electron microscopy (TEM) indicated that the AgNPs were incorporated in the PMMA/PEI core–shell matrix, and had 6–10nm in diameter. AgNPs immobilized on PMMA/PEI core–shell particles were also investigated by energy dispersive X-ray spectroscopy analysis mode extended from scanning electron microscopy (SEM/EDS). Furthermore, the presence of AgNPs was found to influence the thermal degradation behavior of PMMA/PEI particle composites as observed through thermogravimetric analysis (TGA).

Electron Spin Resonance Analysis of Radiation-Induced Free Radicals in Shells and Membranes of Different Poultry Eggs

Radiation-induced free radicals were investigated in the shells and membranes of ostrich, duck, hen, and quail eggs using electron spin resonance (ESR) spectroscopy. The non-irradiated egg shells and membranes showed a single resonance signal centered at g = 2.0048 ± 0.0001 and 2.0072 ± 0.0002, respectively. Upon irradiation (1–3 kGy), a dose-dependent asymmetric ESR signal centered at g = 1.9998 ± 0.0002 was also determined in all eggshell samples, whereas the membranes were found silent for radiation-specific ESR signals. An X-ray diffraction spectrometric study showed the abundance of calcite minerals in the all egg shells. Radiation-induced and trapped CO33−, CO3−, and CO2− paramagnetic entities in the calcite matrix of egg shells might be responsible for a typical ESR signal. The ESR-based identification of all irradiated eggshells was easily possible in practical dose range (1–3 kGy).

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.

Developmental role of dpp in the gastropod shell plate and co-option of the dpp signaling pathway in the evolution of the operculum

The operculum is a novel structure in gastropod molluscs. Because the operculum shows notable similarities to the shell plate, we asked whether there were an evolutionary link between these two secretory organs. We found that some of the genes involved in shell-field development are expressed in the operculum, such as dpp and grainyhead, whereas engrailed and Hox1 are not. Specific knockdown of dpp by injection of double-stranded RNA (dsRNA) resulted in malformation of the shell plate. The shell plate was smaller due to failure of activation of cell proliferation in the shell-field margin. The expressions of grainyhead and chitin synthase 1 in the shell field margin were suppressed by dpp-dsRNA. However, matrix secretion was not completely abolished, and the expressions of ferritin, engrailed or Hox1 were not affected by dpp-dsRNA, indicating that dpp is partly involved in the developmental pathway for shell matrix secretion. We also present evidence that dpp performs a key role in operculum development. Indeed, dpp-dsRNA impaired matrix secretion in the operculum as well as expression of grainyhead. Based on these observations that dpp is important for development of both the shell plate and operculum, we conclude that co-option of dpp to the posterior part of the foot contributed to the innovation of the operculum in gastropods.

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 formation and mineralization of mollusk shell

In the last years, the field of mollusk biomineralization has known a tremendous mutation. The most recent advances deal with the nanostructure of shell biominerals, and with the identification of several shell matrix proteins: on one hand, the complex hierarchical organization of shell biominerals has been deciphered in few models, like nacre. On the other hand, although proteins represent a minor shell component, they are the major macromolecules that control biocrystal synthesis. Until recently, the paradigm was to consider that this control occurs by two antagonist mechanisms: crystal nucleation and growth inhibition. Emerging models try to translate a more complex reality, illustrated by the huge variety of shell proteins, characterized so far. The primary structure of many of them is composed of different functional domains, some of which exhibit enzymatic activity, while others may be involved in cell signalling. Many of them have unknown functions. Today, the shell matrix appears as a whole system, which regulates protein-mineral, protein-protein, and epithelium-mineral interactions. These aspects should be taken in account for the future models of shell formation.

In-depth proteomic analysis of a mollusc shell: acid-soluble and acid-insoluble matrix of the limpet Lottia gigantea

BackgroundInvertebrate biominerals are characterized by their extraordinary functionality and physical properties, such as strength, stiffness and toughness that by far exceed those of the pure mineral component of such composites. This is attributed to the organic matrix, secreted by specialized cells, which pervades and envelops the mineral crystals. Despite the obvious importance of the protein fraction of the organic matrix, only few in-depth proteomic studies have been performed due to the lack of comprehensive protein sequence databases. The recent public release of the gastropod Lottia gigantea genome sequence and the associated protein sequence database provides for the first time the opportunity to do a state-of-the-art proteomic in-depth analysis of the organic matrix of a mollusc shell.ResultsUsing three different sodium hypochlorite washing protocols before shell demineralization, a total of 569 proteins were identified in Lottia gigantea shell matrix. Of these, 311 were assembled in a consensus proteome comprising identifications contained in all proteomes irrespective of shell cleaning procedure. Some of these proteins were similar in amino acid sequence, amino acid composition, or domain structure to proteins identified previously in different bivalve or gastropod shells, such as BMSP, dermatopontin, nacrein, perlustrin, perlucin, or Pif. In addition there were dozens of previously uncharacterized proteins, many containing repeated short linear motifs or homorepeats. Such proteins may play a role in shell matrix construction or control of mineralization processes.ConclusionsThe organic matrix of Lottia gigantea shells is a complex mixture of proteins comprising possible homologs of some previously characterized mollusc shell proteins, but also many novel proteins with a possible function in biomineralization as framework building blocks or as regulatory components. We hope that this data set, the most comprehensive available at present, will provide a platform for the further exploration of biomineralization processes in molluscs.

A novel silk-like shell matrix gene is expressed in the mantle edge of the Pacific oyster prior to shell regeneration

During shell formation, little is known about the functions of organic matrices, especially about the biomineralization of shell prismatic layer. We identified a novel gene, shelk2, from the Pacific oyster presumed to be involved in the shell biosynthesis. The Pacific oyster has multiple copies of shelk2. Shelk2 mRNA is specifically expressed on the mantle edge and is induced during shell regeneration, thereby suggesting that Shelk2 is involved in shell biosynthesis. To our surprise, the database search revealed that it encodes a spider silk-like alanine-rich protein. Interestingly, most of the Shelk2 primary structure is composed of two kinds of poly-alanine motifs—GXNAn(S) and GSAn(S)—where X denotes Gln, Arg or no amino acid. Occurrence of common motifs of Shelk2 and spider silk led us to the assumption that shell and silk are constructed under similar strategies despite of their living environments.

The shell matrix of the pulmonate land snail Helix aspersa maxima

In mollusks, the shell mineralization process is controlled by an array of proteins, glycoproteins and polysaccharides that collectively constitute the shell matrix. In spite of numerous researches, the shell protein content of a limited number of model species has been investigated. This paper presents biochemical data on the common edible land snail Helix aspersa maxima, a model organism for ecotoxicological purposes, which has however been poorly investigated from a biomineralization viewpoint. The shell matrix of this species was extracted and analyzed biochemically for functional in vitro inhibition assay, for amino acid and monosaccharides compositions. The matrix was further analyzed on 1 and 2D gels and short partial protein sequences were obtained from 2D gel spots. Serological comparisons were established with a set of heterologous antibodies, two of which were subsequently used for subsequent immunogold localization of matrix components. Our data suggest that the shell matrix of Helix aspersa maxima may differ widely from the shell secretory repertoire of the marine mollusks studied so far, such as the gastropod Haliotis or the pearl oyster Pinctada. In particular, most of the biochemical properties generally attributed to soluble shell matrices, such as calcium-binding capability, or the capacity to interfere in vitro with the precipitation of calcium carbonate or to inhibit the precipitation of calcium carbonate, were not recorded with this matrix. This drastic change in the biochemical properties of the landsnail shell matrix puts into question the existence of a unique molecular model for molluscan shell formation, and may be related to terrestrialisation.

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.

Identification of Genes Directly Involved in Shell Formation and Their Functions in Pearl Oyster, Pinctada fucata

Mollusk shell formation is a fascinating aspect of biomineralization research. Shell matrix proteins play crucial roles in the control of calcium carbonate crystallization during shell formation in the pearl oyster, Pinctada fucata. Characterization of biomineralization-related genes during larval development could enhance our understanding of shell formation. Genes involved in shell biomineralization were isolated by constructing three suppression subtractive hybridization (SSH) libraries that represented genes expressed at key points during larval shell formation. A total of 2,923 ESTs from these libraries were sequenced and gave 990 unigenes. Unigenes coding for secreted proteins and proteins with tandem-arranged repeat units were screened in the three SSH libraries. A set of sequences coding for genes involved in shell formation was obtained. RT-PCR and in situ hybridization assays were carried out on five genes to investigate their spatial expression in several tissues, especially the mantle tissue. They all showed a different expression pattern from known biomineralization-related genes. Inhibition of the five genes by RNA interference resulted in different defects of the nacreous layer, indicating that they all were involved in aragonite crystallization. Intriguingly, one gene (UD_Cluster94.seq.Singlet1) was restricted to the ‘aragonitic line’. The current data has yielded for the first time, to our knowledge, a suite of biomineralization-related genes active during the developmental stages of P.fucata, five of which were responsible for nacreous layer formation. This provides a useful starting point for isolating new genes involved in shell formation. The effects of genes on the formation of the ‘aragonitic line’, and other areas of the nacreous layer, suggests a different control mechanism for aragonite crystallization initiation from that of mature aragonite growth.

Molecular Evolution of Mollusc Shell Proteins: Insights from Proteomic Analysis of the Edible Mussel Mytilus

Shell matrix proteins (SMPs) that are embedded within calcified layers of mollusc shells are believed to play an essential role in controlling the biomineral synthesis and in increasing its mechanical properties. Among the wide diversity of mollusc shell textures, nacro-prismatic shells represent a tremendous opportunity for the investigation of the SMP evolution. Indeed, nacro-prismatic texture appears early in Cambrian molluscs and is still present in the shell of some bivalves, gastropods, cephalopods and very likely also, of some monoplacophorans. One key question is to know whether these shells are constructed from similar matrix protein assemblages, i.e. whether they share a common origin. Most of the molecular data published so far are restricted to two genera, the bivalve Pinctada and the gastropod Haliotis. The shell protein content of these two genera are clearly different, suggesting independent origins or considerable genetic drift from a common ancestor. In order to describe putatively conserved mollusc shell proteins, here we have investigated the SMP set of a new bivalve model belonging to another genera, the edible mussel Mytilus, using an up-to-date proteomic approach based on the interrogation of more than 70,000 EST sequences, recently available from NCBI public databases. We describe nine novel SMPs, among which three are completely novel, four are homologues of Pinctada SMPs and two are very likely homologues of Haliotis SMPs. This latter result constitutes the first report of conserved SMPs between bivalves and gastropods. More generally, our data suggest that mollusc SMP set may follow a mosaic pattern within the different mollusc models (Mytilus, Pinctada, Haliotis). We discuss the function of such proteins in calcifying matrices, the molecular evolution of SMP genes and the origin of mollusc nacro-prismatic SMPs.

Alternative mechanisms of increased eggshell hardness of avian brood parasites relative to host species

Obligate brood parasitic birds lay their eggs in nests of other species and parasite eggs typically have evolved greater structural strength relative to host eggs. Increased mechanical strength of the parasite eggshell is an adaptation that can interfere with puncture ejection behaviours of discriminating hosts. We investigated whether hardness of eggshells is related to differences between physical and chemical traits from three different races of the parasitic common cuckoo Cuculus canorus, and their respective hosts. Using tools developed for materials science, we discovered a novel correlate of increased strength of parasite eggs: the common cuckoo's egg exhibits a greater microhardness, especially in the inner region of the shell matrix, relative to its host and sympatric non-host species. We then tested predictions of four potential mechanisms of shell strength: (i) increased relative thickness overall, (ii) greater proportion of the structurally harder shell layers, (iii) higher concentration of inorganic components in the shell matrix, and (iv) elevated deposition of a high density compound, MgCO(3), in the shell matrix. We confirmed support only for hypothesis (i). Eggshell characteristics did not differ between parasite eggs sampled from different host nests in distant geographical sites, suggesting an evolutionarily shared microstructural mechanism of stronger parasite eggshells across diverse host-races of brood parasitic cuckoos.

Development and evaluation of dual controlled release microballoons containing riboflavin and citric acid: in vitro and in vivo evaluation

The objective of this work was to optimize the incorporation of citric acid (CA) in the gastroretentive microballoons containing riboflavin (RF) in order to achieve dual controlled release system and consequently enhance the bioavailability of RF. Microballoons of 739 ± 1.9 µm containing RF–CA were prepared by modified emulsion solvent diffusion method and were evaluated both for in vitro and in vivo performance. RF–CA microballoons with 22.8% RF and 37.2% CA entrapped in the shell matrix composed of Eudragit® S 100 and HPMCK4M and in vitro buoyancy of 86.0 ± 0.88% (RCM3) was selected for further studies. RCM3 exhibited biphasic, pH-dependent in vitro dual controlled release of RF (0.9933–0.9962) and CA (0.996–0.9984) beyond 1 h in both simulated fasted and fed state conditions. RCM3 was able to achieve higher mean plasma concentrations than reference formulation RM2 (RF microballoon) both in fed and fasted states in rabbits. The mean AUC0–24 estimate of RCM3 was 55% higher in fasted state (p < 0.01) and about 51% higher in fed state (p < 0.05) relative to mean AUC0–24 from RM2 formulation. Conclusively, enhancement in RF in the presence of CA along the entire plasma level curve suggests a possibility of reduction in dosing frequency. This controlled release drug delivery system of RF, where CA is incorporated in the microballoons can be easily encapsulated in capsule dosage form negating the need of CA solution as vehicle for administration of RF microballoons.

Novel Proteins from the Calcifying Shell Matrix of the Pacific Oyster Crassostrea gigas

The shell of the Pacific oyster Crassostrea gigas is composed of more than 99% CaCO₃ and of around 0.5% of occluded organic matrix. According to classical views, this matrix is supposed to regulate the shell mineral deposition. In this study, we developed one of the first proteomic approaches applied to mollusk shell in order to characterise the calcifying matrix proteins. The insoluble organic matrix, purified after demineralisation of the shell powder, was digested with trypsin enzyme, and separated on nano-LC, prior to nanospray quadrupole/time-of-flight analysis. MS/MS spectra were searched against the above 220,000 EST sequences available in the public database for Crassostrea. Using this approach, we were able to identify partial or full-length sequence transcripts that encode eight novel shell matrix proteins.