A comparative study of the shell matrix protein aspein in pterioid bivalves

The Role of Intrinsically Disordered Proteins in Liquid–Liquid Phase Separation during Calcium Carbonate Biomineralization

Some animal organs contain mineralized tissues. These so-called hard tissues are mostly deposits of calcium salts, usually in the form of calcium phosphate or calcium carbonate. Examples of this include fish otoliths and mammalian otoconia, which are found in the inner ear, and they are an essential part of the sensory system that maintains body balance. The composition of ear stones is quite well known, but the role of individual components in the nucleation and growth of these biominerals is enigmatic. It is sure that intrinsically disordered proteins (IDPs) play an important role in this aspect. They have an impact on the shape and size of otoliths. It seems probable that IDPs, with their inherent ability to phase separate, also play a role in nucleation processes. This review discusses the major theories on the mechanisms of biomineral nucleation with a focus on the importance of protein-driven liquid–liquid phase separation (LLPS). It also presents the current understanding of the role of IDPs in the formation of calcium carbonate biominerals and predicts their potential ability to drive LLPS.

Evolution of EGF-like and Zona pellucida domains containing shell matrix proteins in mollusks

Several types of shell matrix proteins (SMPs) have been identified in molluskan shells. Their diversity is the consequence of various molecular processes, including domain shuffling and gene duplication. However, the evolutionary origin of most SMPs remains unclear. In this study, we investigated the evolutionary process EGF-like and zona pellucida (ZP) domains containing SMPs. Two types of the proteins (EGF-like protein (EGFL) and EGF-like and ZP domains containing protein (EGFZP)) were found in the pearl oyster, Pinctada fucata. In contrast, only EGFZP was identified in the gastropods. Phylogenetic analysis and genomic arrangement studies showed that EGFL and EGFZP formed a clade in bivalves, and their encoding genes were localized in tandem repeats on the same scaffold. In P. fucata, EGFL genes were expressed in the outer part of mantle epithelial cells are related to the calcitic shell formation. However, in both P. fucata and the limpet Nipponacmea fuscoviridis, EGFZP genes were expressed in the inner part of the mantle epithelial cells are related to aragonitic shell formation. Furthermore, our analysis showed that in P. fucata, the ZP domain interacts with eight SMPs that have various functions in the nacreous shell mineralization. The data suggest that the ZP domain can interact with other SMPs, and EGFL evolution in pterimorph bivalves represents an example of neo-functionalization that involves the acquisition of a novel protein through gene duplication.

Molecular cloning and functional characterization of KCNQ1 in shell biomineralisation of pearl oyster Pinctada fucata martensii

KCNQ1, a voltage-gated potassium ion channel, plays an important role in various physiological processes, including osteoblast differentiation in higher animals. However, its function in lower invertebrates such as marine shellfish remains poorly understood. Pearl oysters, such as P. fucata martensii, are ideal for studying biomineralisation. In this study, a full-length cDNA of KCNQ1 from P. fucata martensii (PfKCNQ1) was obtained, and its function in shell formation was investigated. The full-length 3945 bp cDNA of PfKCNQ1 included an open reading frame (ORF) of 1944 bp encoding a polypeptide of 647 amino acids. Multiple sequence alignment revealed high homology with KCNQ1 from other species, with six transmembrane domains (S1 - S6) and a pore (P) region. Expression pattern analysis showed that PfKCNQ1 was expressed in all tested tissues, with highest expression in mantle and heart, and shell notching induced PfKCNQ1 expression. Silencing PfKCNQ1 expression inhibited PfKCNQ1 expression and downregulated four biomineralisation-related genes (Shematrin, Pif80, N16 and MSI60). Disordered crystals or "hollows" were visible in the shell ultrastructure by scanning electron microscopy following PfKCNQ1 knockdown. The results suggested that PfKCNQ1 may participate in or regulate biomineralisation and shell formation in pearl oyster.

Microstructural and Genetic Insights Into the Formation of the “Winter Diffusion Layer” in Japanese Pearl Oyster Pinctada fucata and Its Relation to Environmental Temperature Changes

Phenotypic plasticity in molluscan shell microstructures may be related to environmental changes. The “winter diffusion layer,” a shell microstructure of the Japanese pearl oyster Pinctada fucata, is an example of this phenomenon. In this study, we used P. fucata specimens with shared genetic background to evaluate the seasonal plasticity of shell microstructures, at molecular level. To detect the seasonal changes in shell microstructure and mineral composition, shells of multiple individuals were periodically collected and analyzed using scanning electron microscopy and Raman spectrophotometry. Our observations of the winter diffusion layer revealed that this irregular shell layer, located between the outer and middle shell layers, had a sphenoid shape in radial section. This distinct shape might be caused by the internal extension of the outer shell layer resulting from growth halts. The winter diffusion layer could be distinguished from the calcitic outer shell layer by its aragonitic components and microstructures. Moreover, the components of the winter diffusion layer were irregular simple prismatic (the outer and inner sublayers) and homogeneous structures (the middle sublayer). This irregular formation occurred until April, when the animals resumed their “normal” shell formation after hibernation. To check for a correlation between gene expression and the changes in microstructures, we conducted qPCR of seven major biomineralization-related shell matrix protein-coding genes (aspein, prismalin-14, msi7, msi60, nacrein, n16, and n19) in the shell-forming mantle tissue. Tissue samples were collected from the mantle edge (tissue secreting the outer shell layer) and mantle pallium (where the middle shell layer is constructed) of the same individuals used for microstructural observation and mineral identification that were collected in January (winter growth break period), April (irregular shell formation period), and August (normal shell formation period). Statistically significant differences in gene expression levels were observed between mantle edge and mantle pallium, but no seasonal differences were detected in the seasonal expression patterns of these genes. These results suggest that the formation of the irregular shell layer in P. fucata is caused by a currently unknown genetic mechanism unrelated to the genes targeted in the present study. Further studies using big data (transcriptomics and manipulation of gene expression) are required to answer the questions herein raised. Nevertheless, the results herein presented are essential to unravel the intriguing mystery of the formation of the winter diffusion layer, which may allow us to understand how marine mollusks adapt or acclimate to climate changes.

The 'Shellome' of the Crocus Clam Tridacna crocea Emphasizes Essential Components of Mollusk Shell Biomineralization

Molluscan shells are among the most fascinating research objects because of their diverse morphologies and textures. The formation of these delicate biomineralized structures is a matrix-mediated process. A question that arises is what are the essential components required to build these exoskeletons. In order to understand the molecular mechanisms of molluscan shell formation, it is crucial to identify organic macromolecules in different shells from diverse taxa. In the case of bivalves, however, taxon sampling in previous shell proteomics studies are focused predominantly on representatives of the class Pteriomorphia such as pearl oysters, edible oysters and mussels. In this study, we have characterized the shell organic matrix from the crocus clam, Tridacna crocea, (Heterodonta) using various biochemical techniques, including SDS-PAGE, FT-IR, monosaccharide analysis, and enzyme-linked lectin assay (ELLA). Furthermore, we have identified a number of shell matrix proteins (SMPs) using a comprehensive proteomics approach combined to RNA-seq. The biochemical studies confirmed the presence of proteins, polysaccharides, and sulfates in the T. crocea shell organic matrix. Proteomics analysis revealed that the majority of the T. crocea SMPs are novel and dissimilar to known SMPs identified from the other bivalve species. Meanwhile, the SMP repertoire of the crocus clam also includes proteins with conserved functional domains such as chitin-binding domain, VWA domain, and protease inhibitor domain. We also identified BMSP (Blue Mussel Shell Protein, originally reported from Mytilus), which is widely distributed among molluscan shell matrix proteins. Tridacna SMPs also include low-complexity regions (LCRs) that are absent in the other molluscan genomes, indicating that these genes may have evolved in specific lineage. These results highlight the diversity of the organic molecules – in particular proteins – that are essential for molluscan shell formation.

Evolution of Biomineralization Genes in the Prismatic Layer of the Pen Shell Atrina pectinata

Molluscan shells are composed of calcium carbonates, with small amounts of extracellular matrices secreted from mantle epithelial cells. Many types of shell matrix proteins (SMPs) have been identified from molluscan shells or mantle cells. The pen shell Atrina pectinata (Pinnidae) has two different shell microstructures, the nacreous and prismatic layers. Nacreous and prismatic layer-specific matrix proteins have been reported in Pteriidae bivalves, but remain unclear in Pinnidae. We performed transcriptome analysis using the mantle cells of A. pectinata to screen the candidate transcripts involved in its prismatic layer formation. We found Asprich and nine highly conserved prismatic layer-specific SMPs encoding transcript in P. fucata, P. margaritifera, and P. maxima (Tyrosinase, Chitinase, EGF-like proteins, Fibronectin, valine-rich proteins, and prismatic uncharacterized shell protein 2 [PUSP2]) using molecular phylogenetic analysis or multiple alignment. We confirmed these genes were expressed in the epithelial cells of the mantle edge (outer surface of the outer fold) and the mantle pallium. Phylogenetic character mapping of these SMPs was used to infer a possible evolutionary scenario of them in Pteriomorphia. EGF-like proteins, Fibronectin, and valine-rich proteins encoding genes each evolved in the linage leading to four Pteriomorphia (Mytilidae, Pinnidae, Ostreidae, and Pteriidae), PUSP2 evolved in the linage leading to three Pteriomorphia families (Pinnidae, Ostreidae, and Pteriidae), and chitinase was independently evolved as SMPs in Mytilidae and in other Pteriomorphia (Pinnidae, Ostreidae, and Pteriidae). Our results provide a new dataset for A. pectinata SMP annotation, and a basis for understanding the evolution of prismatic layer formation in bivalves.

Crossing Phenotype Heritability and Candidate Gene Expression in Grafted Black-Lipped Pearl Oyster Pinctada margaritifera, an Animal Chimera

Grafting mantle tissue of a donor pearl oyster into the gonad of a recipient oyster results in the formation of a chimera, the pearl sac. The phenotypic variations of this chimera are hypothesized to be the result of interactions between the donor and recipient genomes. In this study, the heritability of phenotypic variation and its association with gene expression were investigated for the first time during Pinctada margaritifera pearl production. Genetic variance was evaluated at different levels, 1) before the graft operation (expression in graft tissue), 2) after grafting (pearl sac tissue expression in chimera), and 3) on the product of the graft (pearl phenotype traits) based on controlled biparental crosses and the F1 generation. Donor-related genetic parameter estimates clearly demonstrate heritability for nacre weight and thickness, darkness and color, and surface defects and grade, which signifies a genetic basis in the donor oyster. In graft relative gene expression, the value of heritability was superior to 0.20 in for almost all genes; whereas in pearl sac, heritability estimates were low (h2 < 0.10; except for CALC1 and Aspein). Pearl sac expression seems to be more influenced by residual variance than the graft, which can be explained by environmental effects that influence pearls sac gene expression and act as a recipient additive genetic component. The interactions between donor and recipient are very complex, and further research is required to understand the role of the recipient oysters on pearl phenotypic and gene expression variances.

Whole transcriptome sequencing and biomineralization gene architecture associated with cultured pearl quality traits in the pearl oyster, Pinctada margaritifera

Background

Cultured pearls are unique gems produced by living organisms, mainly molluscs of the Pinctada genus, through the biomineralization properties of pearl sac tissue. Improvement of P. margaritifera pearl quality is one of the biggest challenges that Polynesian research has faced to date. To achieve this goal, a better understanding of the complex mechanisms related to nacre and pearl formation is essential and can now be approached through the use of massive parallel sequencing technologies. The aim of this study was to use RNA-seq to compare whole transcriptome expression of pearl sacs that had producing pearls with high and low quality. For this purpose, a comprehensive reference transcriptome of P. margaritifera was built based on multi-tissue sampling (mantle, gonad, whole animal), including different living stages (juvenile, adults) and phenotypes (colour morphotypes, sex).

Results

Strikingly, few genes were found to be up-regulated for high quality pearls (n = 16) compared to the up-regulated genes in low quality pearls (n = 246). Biomineralization genes up-regulated in low quality pearls were specific to prismatic and prism-nacre layers. Alternative splicing was further identified in several key biomineralization genes based on a recent P. margaritifera draft genome.

Conclusion

This study lifts the veil on the multi-level regulation of biomineralization genes associated with pearl quality determination.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5443-5) contains supplementary material, which is available to authorized users.

Insights into the Evolution of Shells and Love Darts of Land Snails Revealed from Their Matrix Proteins

Over the past decade, many skeletal matrix proteins that are possibly related to calcification have been reported in various calcifying animals. Molluscs are among the most diverse calcifying animals and some gastropods have adapted to terrestrial ecological niches. Although many shell matrix proteins (SMPs) have already been reported in molluscs, most reports have focused on marine molluscs, and the SMPs of terrestrial snails remain unclear. In addition, some terrestrial stylommatophoran snails have evolved an additional unique calcified character, called a “love dart,” used for mating behavior. We identified 54 SMPs in the terrestrial snail Euhadra quaesita, and found that they contain specific domains that are widely conserved in molluscan SMPs. However, our results also suggest that some of them possibly have evolved independently by domain shuffling, domain recruitment, or gene co-option. We then identified four dart matrix proteins, and found that two of them are the same proteins as those identified as SMPs. Our results suggest that some dart matrix proteins possibly have evolved by independent gene co-option from SMPs during dart evolution events. These results provide a new perspective on the evolution of SMPs and “love darts” in land snails.

In-depth proteomic analyses of Haliotis laevigata (greenlip abalone) nacre and prismatic organic shell matrix

Background

The shells of various Haliotis species have served as models of invertebrate biomineralization and physical shell properties for more than 20 years. A focus of this research has been the nacreous inner layer of the shell with its conspicuous arrangement of aragonite platelets, resembling in cross-section a brick-and-mortar wall. In comparison, the outer, less stable, calcitic prismatic layer has received much less attention. One of the first molluscan shell proteins to be characterized at the molecular level was Lustrin A, a component of the nacreous organic matrix of Haliotis rufescens. This was soon followed by the C-type lectin perlucin and the growth factor-binding perlustrin, both isolated from H. laevigata nacre, and the crystal growth-modulating AP7 and AP24, isolated from H. rufescens nacre. Mass spectrometry-based proteomics was subsequently applied to to Haliotis biomineralization research with the analysis of the H. asinina shell matrix and yielded 14 different shell-associated proteins. That study was the most comprehensive for a Haliotis species to date.

Methods

The shell proteomes of nacre and prismatic layer of the marine gastropod Haliotis laevigata were analyzed combining mass spectrometry-based proteomics and next generation sequencing.

Results

We identified 297 proteins from the nacreous shell layer and 350 proteins from the prismatic shell layer from the green lip abalone H. laevigata. Considering the overlap between the two sets we identified a total of 448 proteins. Fifty-one nacre proteins and 43 prismatic layer proteins were defined as major proteins based on their abundance at more than 0.2% of the total. The remaining proteins occurred at low abundance and may not play any significant role in shell fabrication. The overlap of major proteins between the two shell layers was 17, amounting to a total of 77 major proteins.

Conclusions

The H. laevigata shell proteome shares moderate sequence similarity at the protein level with other gastropod, bivalve and more distantly related invertebrate biomineralising proteomes. Features conserved in H. laevigata and other molluscan shell proteomes include short repetitive sequences of low complexity predicted to lack intrinsic three-dimensional structure, and domains such as tyrosinase, chitin-binding, and carbonic anhydrase. This catalogue of H. laevigata shell proteins represents the most comprehensive for a haliotid and should support future efforts to elucidate the molecular mechanisms of shell assembly.

Electronic supplementary material

The online version of this article (10.1186/s12953-018-0139-3) contains supplementary material, which is available to authorized users.

Amyloid Assembly Endows Gad m 1 with Biomineralization Properties

Acid proteins capable of nucleating Ca²⁺ and displaying aggregation capacity play key roles in the formation of calcium carbonate biominerals. The helix-loop helix EF-hands are the most common Ca²⁺-binding motifs in proteins. Calcium is bound by the loop region. These motifs are found in many proteins that are regulated by calcium. Gad m 1, an Atlantic cod β-parvalbumin isoform, is a monomeric EF-hand protein that acts as a Ca²⁺ buffer in fish muscle; the neutral and acid apo-forms of this protein can form amyloids. Since Ca²⁺-nucleating proteins have a propensity to form extended β-strand structures, we wondered whether amyloid assemblies of an EF-hand protein were able to influence calcium carbonate crystallization in vitro. Here, we used the Gad m 1 chain as a model to generate monomeric and amyloid assemblies and to analyze their effect on calcite formation in vitro. We found that only amyloid assemblies alter calcite morphology.

Influence of water temperature and food on the last stages of cultured pearl mineralization from the black-lip pearl oyster Pinctada margaritifera

Environmental parameters, such as food level and water temperature, have been shown to be major factors influencing pearl oyster shell growth and molecular mechanisms involved in this biomineralization process. The present study investigates the effect of food level (i.e., microalgal concentration) and water temperature, in laboratory controlled conditions, on the last stages of pearl mineralization in order to assess their impact on pearl quality. To this end, grafted pearl oysters were fed at different levels of food and subjected to different water temperatures one month prior to harvest to evaluate the effect of these factors on 1) pearl and shell deposition rate, 2) expression of genes involved in biomineralization in pearl sacs, 3) nacre ultrastructure (tablet thickness and number of tablets deposited per day) and 4) pearl quality traits. Our results revealed that high water temperature stimulates both shell and pearl deposition rates. However, low water temperature led to thinner nacre tablets, a lower number of tablets deposited per day and impacted pearl quality with better luster and fewer defects. Conversely, the two tested food level had no significant effects on shell and pearl growth, pearl nacre ultrastructure or pearl quality. However, one gene, Aspein, was significantly downregulated in high food levels. These results will be helpful for the pearl industry. A wise strategy to increase pearl quality would be to rear pearl oysters at a high water temperature to increase pearl growth and consequently pearl size; and to harvest pearls after a period of low water temperature to enhance luster and to reduce the number of defects.

Environmental and Genetic Determinants of Biofilm Formation in Paracoccus denitrificans

The bacterium Paracoccus denitrificans is a model for the process of denitrification, by which nitrate is reduced to dinitrogen during anaerobic growth. Denitrification is important for soil fertility and greenhouse gas emission and in waste and water treatment processes. The ability of bacteria to grow as a biofilm attached to a solid surface is important in many different contexts. In this paper, we report that attached growth of P. denitrificans is stimulated by nitric oxide, an intermediate in the denitrification pathway. We also show that calcium ions stimulate attached growth, and we identify a large calcium binding protein that is required for growth on a polystyrene surface. We identify components of a signaling pathway through which nitric oxide may regulate biofilm formation. Our results point to an intimate link between metabolic processes and the ability of P. denitrificans to grow attached to a surface.

The genome of the denitrifying bacterium Paracoccus denitrificans predicts the expression of a small heme-containing nitric oxide (NO) binding protein, H-NOX. The genome organization and prior work in other bacteria suggest that H-NOX interacts with a diguanylate cyclase that cyclizes GTP to make cyclic di-GMP (cdGMP). Since cdGMP frequently regulates attached growth as a biofilm, we first established conditions for biofilm development by P. denitrificans. We found that adhesion to a polystyrene surface is strongly stimulated by the addition of 10 mM Ca²⁺ to rich media. The genome encodes at least 11 repeats-in-toxin family proteins that are predicted to be secreted by the type I secretion system (TISS). We deleted the genes encoding the TISS and found that the mutant is almost completely deficient for attached growth. Adjacent to the TISS genes there is a potential open reading frame encoding a 2,211-residue protein with 891 Asp-Ala repeats. This protein is also predicted to bind calcium and to be a TISS substrate, and a mutant specifically lacking this protein is deficient in biofilm formation. By analysis of mutants and promoter reporter fusions, we show that biofilm formation is stimulated by NO generated endogenously by the respiratory reduction of nitrite. A mutant lacking both predicted diguanylate cyclases encoded in the genome overproduces biofilm, implying that cdGMP is a negative regulator of attached growth. Our data are consistent with a model in which there are H-NOX-dependent and -independent pathways by which NO stimulates biofilm formation.

IMPORTANCE The bacterium Paracoccus denitrificans is a model for the process of denitrification, by which nitrate is reduced to dinitrogen during anaerobic growth. Denitrification is important for soil fertility and greenhouse gas emission and in waste and water treatment processes. The ability of bacteria to grow as a biofilm attached to a solid surface is important in many different contexts. In this paper, we report that attached growth of P. denitrificans is stimulated by nitric oxide, an intermediate in the denitrification pathway. We also show that calcium ions stimulate attached growth, and we identify a large calcium binding protein that is required for growth on a polystyrene surface. We identify components of a signaling pathway through which nitric oxide may regulate biofilm formation. Our results point to an intimate link between metabolic processes and the ability of P. denitrificans to grow attached to a surface.

Characterization of transcriptome and identification of biomineralization genes in winged pearl oyster (Pteria penguin) mantle tissue

The winged pearl oyster Pteria penguin is a commercially important marine pearl oyster species, with pearls that are quite different from those of other pearl oysters. Among such species, mantle tissue is the main organ responsible for shell and pearl formation, a biomineralization process that is regulated by a series of genes, most of which remain unknown. In this study, we sequenced and characterized the transcriptome of P. penguin mantle tissue using the HiSeq 2000 sequencing platform. A total of 93,204 unique transcripts were assembled from 51,580,076 quality reads, with a mean length of 608bp, and 40,974 unigenes were annotated. The sequence data enabled the identification of 79,702 potential single nucleotide polymorphism loci and 4345 putative simple sequence repeat loci. A total of 71 unique transcripts were identified homologous to known biomineralization genes, including mantle gene, nacrein, pearlin, pif, chitinase, and shematrin, of which only 3 were previously reported in P. penguin. qPCR analysis indicated that 10 randomly selected biomineralization genes were much more highly expressed in mantle tissue than in the other tissues. In addition, 30 unique sequences were identified as highly expressed, with FPKM values of >3000, and most of these were biomineralization-related genes, including shematrin family genes, a jacalin-related lectin synthesis gene, calponin-2, and paramyosin. These findings will be useful for future studies of biomineralization in P. penguin, as well as in other Pteria species.

Sea shell diversity and rapidly evolving secretomes: insights into the evolution of biomineralization

An external skeleton is an essential part of the body plan of many animals and is thought to be one of the key factors that enabled the great expansion in animal diversity and disparity during the Cambrian explosion. Molluscs are considered ideal to study the evolution of biomineralization because of their diversity of highly complex, robust and patterned shells. The molluscan shell forms externally at the interface of animal and environment, and involves controlled deposition of calcium carbonate within a framework of macromolecules that are secreted from the dorsal mantle epithelium. Despite its deep conservation within Mollusca, the mantle is capable of producing an incredible diversity of shell patterns, and macro- and micro-architectures. Here we review recent developments within the field of molluscan biomineralization, focusing on the genes expressed in the mantle that encode secreted proteins. The so-called mantle secretome appears to regulate shell deposition and patterning and in some cases becomes part of the shell matrix. Recent transcriptomic and proteomic studies have revealed marked differences in the mantle secretomes of even closely-related molluscs; these typically exceed expected differences based on characteristics of the external shell. All mantle secretomes surveyed to date include novel genes encoding lineage-restricted proteins and unique combinations of co-opted ancient genes. A surprisingly large proportion of both ancient and novel secreted proteins containing simple repetitive motifs or domains that are often modular in construction. These repetitive low complexity domains (RLCDs) appear to further promote the evolvability of the mantle secretome, resulting in domain shuffling, expansion and loss. RLCD families further evolve via slippage and other mechanisms associated with repetitive sequences. As analogous types of secreted proteins are expressed in biomineralizing tissues in other animals, insights into the evolution of the genes underlying molluscan shell formation may be applied more broadly to understanding the evolution of metazoan biomineralization.

Stepwise Evolution of Coral Biomineralization Revealed with Genome-Wide Proteomics and Transcriptomics

Despite the importance of stony corals in many research fields related to global issues, such as marine ecology, climate change, paleoclimatogy, and metazoan evolution, very little is known about the evolutionary origin of coral skeleton formation. In order to investigate the evolution of coral biomineralization, we have identified skeletal organic matrix proteins (SOMPs) in the skeletal proteome of the scleractinian coral, Acropora digitifera, for which large genomic and transcriptomic datasets are available. Scrupulous gene annotation was conducted based on comparisons of functional domain structures among metazoans. We found that SOMPs include not only coral-specific proteins, but also protein families that are widely conserved among cnidarians and other metazoans. We also identified several conserved transmembrane proteins in the skeletal proteome. Gene expression analysis revealed that expression of these conserved genes continues throughout development. Therefore, these genes are involved not only skeleton formation, but also in basic cellular functions, such as cell-cell interaction and signaling. On the other hand, genes encoding coral-specific proteins, including extracellular matrix domain-containing proteins, galaxins, and acidic proteins, were prominently expressed in post-settlement stages, indicating their role in skeleton formation. Taken together, the process of coral skeleton formation is hypothesized as: 1) formation of initial extracellular matrix between epithelial cells and substrate, employing pre-existing transmembrane proteins; 2) additional extracellular matrix formation using novel proteins that have emerged by domain shuffling and rapid molecular evolution and; 3) calcification controlled by coral-specific SOMPs.

Mantle Branch-Specific RNA Sequences of Moon Scallop Amusium pleuronectes to Identify Shell Color-Associated Genes

Amusium pleuronectes (Linnaeus) that secretes red- and white-colored valves in two branches of mantle tissues is an excellent model for shell color research. High-throughput transcriptome sequencing and profiling were applied in this project to reveal the detailed molecular mechanism of this phenotype differentiation. In this study, 50,796,780 and 54,361,178 clean reads were generated from the left branch (secreting red valve, RS) and right branch (secreting white valve, WS) using the Illumina Hiseq 2000 platform. De novo assembly generated 149,375 and 176,652 unigenes with an average length of 764 bp and 698 bp in RS and WS, respectively. Kyoto encyclopedia of genes and genomes (KEGG) metabolic pathway analysis indicated that the differentially expressed genes were involved in 228 signaling pathways, and 43 genes were significantly enriched (P<0.01). Nineteen of 20 differentially expressed vitellogenin genes showed significantly high expression in RS, which suggested that they probably played a crucial role in organic pigment assembly and transportation of the shell. Moreover, 687 crystal formation-related (or biomineralization-related) genes were detected in A. pleuronectes, among which 144 genes exhibited significant difference between the two branches. Those genes could be classified into shell matrix framework participants, crystal nucleation and growth-related elements, upstream regulation factors, Ca level regulators, and other classifications. We also identified putative SNP and SSR markers from these samples which provided the markers for genetic diversity analysis, genetic linkage, QTL analysis. These results provide insight into the complexity of shell color differentiation in A. pleuronectes so as valuable resources for further research.

Biomineral proteins from Mytilus edulis mantle tissue transcriptome

The common blue mussel, Mytilus edulis, has a bimineralic shell composed of approximately equal proportions of the two major polymorphs of calcium carbonate: calcite and aragonite. The exquisite biological control of polymorph production is the focus of research interest in terms of understanding the details of biomineralisation and the proteins involved in the process of complex shell formation. Recent advances in ease and availability of pyrosequencing and assembly have resulted in a sharp increase in transcriptome data for invertebrate biominerals. We have applied Roche 454 pyrosequencing technology to profile the transcriptome for the mantle tissue of the bivalve M. edulis. A comparison was made between the results of several assembly programs: Roche Newbler assembler versions 2.3, 2.5.2 and 2.6 and MIRA 3.2.1 and 3.4.0. The Newbler and MIRA assemblies were subsequently merged using the CAP3 assembler to give a higher consensus in alignments and a more accurate estimate of the true size of the M. edulis transcriptome. Comparison sequence searches show that the mantle transcripts for M. edulis encode putative proteins exhibiting sequence similarities with previously characterised shell proteins of other species of Mytilus, the Bivalvia Pinctada and haliotid gastropods. Importantly, this enhanced transcriptome has detected several transcripts that encode proteins with sequence similarity with previously described shell biomineral proteins including Shematrins and lysine-rich matrix proteins (KRMPs) not previously found in Mytilus.

A history of the cultured pearl industry

During the 18th and 19th centuries, studies of how pearls are formed were conducted mainly in Europe. The subsequent pearl culturing experiments conducted worldwide in the early 20th century, however, failed to develop into a pearl industry. In Japan, however, Kokichi Mikimoto succeeded in culturing blister pearls in 1893 under the guidance of Kakichi Mitsukuri, a professor at Tokyo Imperial University (now the University of Tokyo) and the first director of the Misaki Marine Biological Station, Graduate School of Science, University of Tokyo. This success and subsequent developments laid the foundation for the pearl farming industry, developed new demand for cultured pearls in the European jewelry market, and initiated the full-scale industrialization of pearl culturing. In addition, research at the Misaki Marine Biological Station resulted in noteworthy advances in the scientific study of pearl formation. Today, pearls are cultured worldwide, utilizing a variety of pearl oysters. The pearl farming industry, with its unique origins in Japan, has grown into a global industry. Recently, the introduction of genome analysis has allowed cultured pearl research to make rapid progress worldwide in such areas as the dynamics of mother-of-pearl layer formation and biomineralization. This signals another new era in the study of pearls.