Isolation, identification, and preparation of tyrosinase inhibitory peptides from Pinctada martensii meat

Recently, natural tyrosinase inhibitors have gained attention in clinical cosmetology research. In this study, the enzymatic hydrolysis of Pinctada martensii meat by protease from Bacillus licheniformis, 401 peptides with tyrosinase inhibitory were identified after isolated by ultrafiltration and Sephadex G-15 from the fraction F4. The peptide effects on the tyrosinase activity and structure were evaluated using molecular docking. Three synthetic peptides classified as W1 (WDRPKDDGGSPIK), W2 (DRGYPPVMF), and W3 (SGGGGGGGLGSGGSIRSSY), which had the lowest binding energies were selected for in vitro synthesis and biological activity investigation. The W3 peptide (5 mg/mL) had the highest tyrosinase activity, SPF, DPPH, and ABTS clearance values, and total antioxidant capacity. W3 did not affect the survival rate of mouse melanoma B16-F10 cells (1.0-5.0 mg/mL) but decreased the melanin content. Hence, W3 could be suitable for multifunctional tyrosinase inhibition and provides a novel method to use marine organisms as natural tyrosinase inhibitor sources.

Exosome-like Nanovesicles Derived from the Mucilage of Pinctada Martensii Exhibit Antitumor Activity against 143B Osteosarcoma Cells

Osteosarcoma is prone to metastasis and has a low long-term survival rate. The drug treatment of osteosarcoma, side effects of treatment drugs, and prognosis of patients with lung metastasis continue to present significant challenges, and the efficacy of drugs used in the treatment of osteosarcoma remains low. The development of new therapeutic drugs is urgently needed. In this study, we successfully isolated Pinctada martensii mucilage exosome-like nanovesicles (PMMENs). Our findings demonstrated that PMMENs inhibited the viability and proliferation of 143B cells, induced apoptosis, and inhibited cell proliferation by suppressing the activation of the ERK1/2 and Wnt signaling pathways. Furthermore, PMMENs inhibited cell migration and invasion by downregulating N-cadherin, vimentin, and matrix metalloprotease-2 protein expression levels. Transcriptomic and metabolomic analyses revealed that differential genes were co-enriched with differential metabolites in cancer signaling pathways. These results suggest that PMMENs may exert anti-tumor activity by targeting the ERK1/2 and Wnt signaling pathways. Moreover, tumor xenograft model experiments showed that PMMENs can inhibit the growth of osteosarcoma in mice. Thus, PMMENs may be a potential anti-osteosarcoma drug.

Protective Effect of Peptides from Pinctada Martensii Meat on the H(2)O(2)-Induced Oxidative Injured HepG2 Cells

Pinctada martensii is a major marine pearl cultured species in southern China, and its meat is rich in protein, which is an excellent material for the preparation of bioactive peptides. In this study, the peptides from Pinctada martensii meat were prepared by simulated gastrointestinal hydrolysis, and after multistep purification, the structures of the peptides were identified, followed by the solid-phase synthesis of the potential antioxidant peptides. Finally, the antioxidant activities of the peptides were verified using HepG2 cells, whose oxidative stress was induced by hydrogen peroxide (H₂O₂). It was shown that the antioxidant peptide (S4) obtained from Pinctada martensii meat could significantly increase the cell viability of HepG2 cells. S4 could also scavenge reactive oxygen species (ROS) and reduce the lactate dehydrogenase (LDH) level. In addition, it could enhance the production of glutathione (GSH) and catalase (CAT) in HepG2 cells, as well as the expression of key genes in the Nrf2 signaling pathway. Three novel antioxidant peptides, arginine-leucine (RL), arginine-glycine-leucine (RGL), and proline-arginine (PR), were also identified. In conclusion, peptides from Pinctada martensii meat and three synthetic peptides (RGL, RL, PR) showed antioxidant activity and could have the potential to be used as antioxidant candidates in functional foods.

The Anti-Photoaging Activity of Peptides from Pinctada martensii Meat

Long-term exposure to ultraviolet-B (UVB) can cause photoaging. Peptides from Pinctada martensii meat have been shown to have anti-photoaging activities, but their mechanism of action is rarely studied. In this study, Pinctada martensii meat hydrolysates (PME) were prepared by digestive enzymes and then separated by ultrafiltration and Sephadex G-25 gel filtration chromatography to obtain a purified fraction (G2). The fraction G2 was identified by ultra-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS), and peptide sequences were synthesized by solid-phase synthesis. The mechanism of anti-photoaging activities was investigated using a human immortalised epidermal (HaCaT) cell model. Results showed that peptides from Pinctada martensii meat increased UVB-induced cell viability and reduced the contents of interstitial collagenase (MMP-1) and matrix lysing enzyme (MMP-3) in HaCaT cells. Furthermore, the fraction of G2 significantly downregulated the expression of p38, EKR, JNK, MMP-1, and MMP-3 in HaCaT cells. The peptide sequences Phe-His (FH), Ala-Leu (AL), Met-Tyr (MY), Ala-Gly-Phe (AGF), and Ile-Tyr-Pro (IYP) were identified and synthesized. Besides, FH reduced the contents of MMP-1 and MMP-3 in HaCaT cells, combining them effectively in molecular docking analysis. Thus, peptides from Pinctada martensii meat showed anti-photoaging activities and might have the potential to be used as an anti-photoaging agent in functional foods.

Production and identification of peptides with activity promoting osteoblast proliferation from meat dregs of Pinctada martensii

As a by-product of pearl production, Pinctada martensii meat dregs have a high level of protein but cannot be fully utilized. In this study, P. martensii meat dregs were first hydrolyzed by three pepsin enzymes, resulting in neutral proteinase enzymatic hydrolysate that had a higher effect on stimulating the proliferation of MC3T3-E1 cells, and cell proliferation increases of 37.37 ± 0.03%. Subsequently, after purification of alcohol precipitation, ultrafiltration, and Superdex G-25 gel chromatography, five fractions were further separated and purified in which fraction ZP2 could effectively improve cell proliferation induced an increase of 43.95 ± 0.03% in MC3T3-E1 cells growth. Consequently, with the help of alkaline phosphatase and methyl thiazolyl tetrazolium assay, five novel peptides (FDNEGKGKLPEEY, FWDGRDGEVDGFK, VLQTDNDALGKAK, IVLDSGDGVTH, and MVAPEEHP) derived from fraction ZP2 with the strongest osteogenic activity were screened, and their sequences were identified using Orbitrap Fusion Lumos Tribrid Orbital liquid chromatography-mass spectrometry. Therefore, the research results demonstrated that P. martensii meat could be used as a promising material for producing food additives for improving osteoporosis. PRACTICAL APPLICATIONS: In this study, after enzymolysis and purification, the fraction ZP2, derived from Pinctada martensii meat dregs were found to have a better activity of promoting osteoblast proliferation, showing the higher osteogenic activity with an increase of 43.95 ± 0.03% in terms of cell proliferation. It is beneficial to realize the high value and resource utilization of P. martensii meat dregs as a by-product of pearl production. The research demonstrated that the meat dregs of P. martensii could be used as an attractive material for producing active peptides in functional foods. In addition, the molecular weight of the peptides we identified from the ZP2 fraction is suitable for the proliferation of MC3T3-E1 cells, which lays a foundation for the further synthesis of peptides that promote the high proliferation activity of osteocytes.

Effect of Oral Administration of Active Peptides of Pinctada Martensii on the Repair of Skin Wounds

Skin wound healing, especially chronic wound healing, is a common challenging clinical problem. It is urgent to broaden the sources of bioactive substances that can safely and efficiently promote skin wound healing. This study aimed to observe the effects of active peptides (APs) of the mantle of Pinctada martensii on wound healing. After physicochemical analysis of amino acids and mass spectrometry of APs, the effect of APs on promoting healing was studied through a whole cortex wound model on the back of mice for 18 consecutive days. The results showed that APs consisted of polypeptides with molecular weights in the range 302.17–2936.43 Da. The content of polypeptides containing 2–15 amino acids accounted for 73.87%, and the hydrophobic amino acids accounted for 56.51%. Results of in vitro experimentation showed that mice in APs-L group which were fed a low dose of APs (0.5 g/kg bw) had a shortened epithelialization time due to a shortening inflammatory period (p < 0.05). Mechanistically, this relied on its specific ability to promote the proliferation of CD31, FGF and EGF which accelerated the percentage of wound closure. Moreover, the APs-L group mice had enhanced collagen synthesis and increased type III collagen content in their wounds through a TGF-β/Smad signaling pathway (p > 0.05). Consequently, scar formation was inhibited and wound healing efficiency was significantly improved. These results show that the APs of Pinctada martensii promote dermal wound healing in mice and have tremendous potential for development and utilization in skin wound healing.

Evaluation of Small Molecular Polypeptides from the Mantle of Pinctada Martensii on Promoting Skin Wound Healing in Mice

Skin wound healing, especially chronic wound healing, is a common challenging clinical problem. It is urgent to broaden the sources of bioactive substances that can safely and efficiently promote skin wound healing. This study aimed to observe the effects of small molecular peptides (SMPs) of the mantle of Pinctada martensii on wound healing. After physicochemical analysis of amino acids and mass spectrometry of SMPs, the effect of SMPs on promoting healing was studied through a whole cortex wound model on the back of mice for 18 consecutive days. The results showed that SMPs consisted of polypeptides with a molecular weight of 302.17-2936.43 Da. The content of polypeptides containing 2-15 amino acids accounted for 73.87%, and the hydrophobic amino acids accounted for 56.51%. Results of in vitro experimentation showed that SMPs possess a procoagulant effect, but no antibacterial activity. Results of in vivo experiments indicated that SMPs inhibit inflammatory response by secretion of anti-inflammatory factor IL-10 during the inflammatory phase; during the proliferative phase, SMPs promote the proliferation of fibroblasts and keratinocytes. The secretion of transforming growth factor-β1 and cyclin D1 accelerates the epithelialization and contraction of wounds. In the proliferative phase, SMPs effectively promote collagen deposition and partially inhibit superficial scar hyperplasia. These results show that SMPs promotes dermal wound healing in mice and have a tremendous potential for development and utilization in skin wound healing.

An integrated metabolomic and proteomic study of toxic effects of Benzo[a]pyrene on gills of the pearl oyster Pinctada martensii

Benzo[a]pyrene (BaP) is one of the most important polycyclic aromatic hydrocarbons (PAHs), which are widely present in the marine environment. Because of its teratogenic, mutagenic, and carcinogenic effects on various organisms, the toxicity of BaP is of great concern. In this study, we focused on the toxic effects of BaP (1 µg/L and 10 µg/L) on gills of the pearl oyster Pinctada martensii using combined metabolomic and proteomic approaches. At the metabolome level, the high concentration of BaP mainly caused abnormal energy metabolism, osmotic regulation and immune response marked by significantly altered metabolites in gills. At the proteome level, both concentrations of BaP mainly induced signal transduction, transcription regulation, cell growth, stress response, and energy metabolism. Overall, the research demonstrated that the combination of proteomic and metabolomic approaches could provide a significant way to elucidate toxic effects of BaP on P. martensii.

Tissue-specific metabolic responses of the pearl oyster Pinctada martensii exposed to benzo[a]pyrene

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) that is well known for its teratogenic, mutagenic and carcinogenic effects. In this study, we applied metabolomics to investigate the tissue-specific metabolic responses of the Pinctada martensii digestive glands and gills after a short-duration exposure to BaP (1 μg/L and 10 μg/L). After 72 h of exposure to BaP, the majority of metabolite changes were related to osmolytes, energy metabolites, and amino acids. BaP (1 μg/L) accelerated energy deterioration and decreased osmotic regulation, while BaP (10 μg/L) disturbed energy metabolism and increased osmotic stress in the digestive glands. Both BaP doses disturbed osmotic regulation and energy metabolism in the gills. BaP also induced neurotoxicity in both tissues. These findings demonstrated that BaP exhibited tissue-specific metabolic responses in P. martensii. The difference in these metabolite responses between the digestive glands and gills might prove to be suitable biomarkers for indicating exposure to specific marine pollutants.

Deep transcriptome profiling sheds light on key players in nucleus implantation induced immune response in the pearl oyster Pinctada martensii

Immunological rejection of the pearl oysters following nucleus implantation is a major issue limiting the successful rate of cultured pearls. To date, the molecular mechanism of immune tolerance during pearl formation in the pearl oysters is still largely unknown. Through the RNA sequencing platform and comparative transcriptomic analysis, we investigated the chronic gene expression changes at seven time points (0, 5, 10, 15, 20, 30, 60 days post implantation or dpi) over a period of 60 days following nucleus implantation in the pearl oyster Pinctada martensii. A total of 81,390 unique transcripts (or unigenes) with a combined length of 96.8 million bp and a N50 value of 2227 bp were obtained. When compared with sequences in the nr, nt, Swiss-Prot, KEGG, COG and GO databases, 36,380 unigenes can find homologous genes. Pairwise comparison of gene expression among all the samples showed that the largest number (or 6846) of differentially expressed genes was observed at 10 dpi. The number then decreased to below 5000 at 15, 20 and 30 dpi and increased again to 6679 at 60 dpi. PCA analysis further showed that the seven time points can be roughly divided into four groups. Comparative transcriptomic analysis between the four groups identified a variety of genes showing differential expression at different time points, including many immune-related genes such as those encoding for toll-like receptor, lectin, scavenger receptor, and peroxidase. In addition, GO and KEGG enrichment analysis revealed that these differentially expressed genes were mainly associated with metabolism, ribosome function, immune response, signaling transduction, and cytoskeleton organization. Notably, two KEGG pathways, namely "cell adhesion molecules" and "primary immunodeficiency" were significantly enriched during the whole process. This finding indicates that genes in these pathways are likely to play critical roles in the immune tolerance of the pearl oysters. To conclude, the data obtained contribute to a better understanding of the molecular mechanisms of nucleus implantation induced immune response in the pearl oysters, and will facilitate the development of effective measures to improve the performance of pearl culture.

Dynamic responses of antioxidant enzymes in pearl oyster Pinctada martensii exposed to di(2-ethylhexyl) phthalate (DEHP)

Di(2-ethylhexyl) phthalate (DEHP) is recognized as one of the most ubiquitous contaminants in marine environments and causes adverse effects on the health of marine organisms. The purpose of this study was to investigate the toxic effects of DEHP on the pearl oyster Pinctada martensii. The Pinctada martensii was exposed to 0.0, 0.5, 2, 8, or 32mgL^-1 DEHP for 7 and 10days using parameters of antioxidant. Antioxidant indicators included levels of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), peroxidase (POD), and total antioxidant capacity (T-AOC) in the gills and hepatopancreas of Pinctada martensii for 7 and 10days. Besides, we used the lowest observed effect concentration (LOEC) of five enzyme activities in different tissues of Pinctada martensii for 7 and 10days to compare sensitivity. The results showed that the gills were more sensitive than the hepatopancreas of Pinctada martensii and that GSH activity in the gills and CAT activity in the hepatopancreas might be suitable biomarkers after 7days of DEHP exposure. After 10days of DEHP exposure, the GSH activity and CAT activity in the gills and SOD activity in the hepatopancreas could be regarded as biomarkers. Compared to the LOEC, GSH activity in the gills and CAT activity in the hepatopancreas after 7days of DEHP exposure were more sensitive than any other biomarkers. In addition, after 10days of DEHP exposure, GSH activity in the gills and hepatopancreas were much more sensitive than other activities. In conclusion, GSH activity demonstrated its potential to be used as a biomarker for the monitoring of DEHP pollution in the marine environment.

Effects of pyrene exposure on immune response and oxidative stress in the pearl oyster, Pinctada martensii

Pyrene is a polycyclic aromatic hydrocarbon (PAH) commonly observed in aquatic ecosystems, which originates primarily from the incomplete combustion of fossil fuels and the use of petroleum compounds. Pyrene can cause the immune disturbance and oxidative stress, result in immunotoxicity, DNA damage, reduce reproduction significantly, and induce behavioral changes. Marine bivalves are commonly used as bioindicators for marine pollution, and hemolymph is a metabolite transfer medium for PAH pollutant. However, the vital immune indicator responses of pearl oyster Pinctada martensii hemolymph exposed to pyrene is still unclear. Thus, the immunotoxic responses of pyrene on the hemolymph of the Pinctada martensii were investigated in this study. After exposure to pyrene for 7 days, the total number of hemocytes (THC), cell membrane stability (CMS), phagocytic activity (PA) and total glutathione (GSH_T) all decreased significantly. Pyrene also caused a significant increase in lipid peroxidation (LPO). Median effective concentrations (EC₅₀) of pyrene on THC (4.5 μg L^-1) and LPO (5.2 μg L^-1) were lower than those for CMS (13.8 μg L^-1), PA (12.1 μg L^-1) and GSH_T (7.2 μg L^-1), which indicates that THC and LPO were more sensitive. Additionally, a clear dose-effect relationship indicated that pyrene stimulated a marked immune response, as well as oxidative stress in P. martensii, which demonstrates the subtle effects of pyrene exposure on marine invertebrates and the potential associated risk.

Pm-miR-133 hosting in one potential lncRNA regulates RhoA expression in pearl oyster Pinctada martensii

Long non-coding RNAs (LncRNAs) are abundant in the genome of higher forms of eukaryotes and implicated in regulating the diversity of biological processes partly because they host microRNAs (miRNAs), which are repressors of target gene expression. In vertebrates, miR-133 regulates the differentiation and proliferation of cardiac and skeletal muscles. Pinctada martensii miR-133 (pm-miR-133) was identified in our previous research through Solexa deep sequencing. In the present study, the precise sequence of mature pm-miR-133 was validated through miR-RACE. Stem loop qRT-PCR analysis demonstrated that mature pm-miR-133 was constitutively expressed in the adductor muscle, gonad, hepatopancreas, mantle, foot, and gill of P. martensii. Among these tissues, the adductor muscle exhibited the highest pm-miR-133 expression. Target analysis indicated that pm-RhoA was the potential regulatory target of pm-miR-133. Bioinformatics analyses revealed that a potential LncRNA (designated as Lnc133) with a mature pm-miR-133 could generate a hairpin structure that was highly homologous to that of Lottia gigantea. Lnc133 was also highly expressed in the adductor muscle, gill, hepatopancreas, and gonad. Phylogenetic analysis further showed that the miR-133s derived from chordate and achordate were separated into two classes. Therefore, Lnc133 hosting pm-miR-133 could be involved in regulating the cell proliferation of adductor muscles by targeting pm-RhoA.

Proteomic and metabolomic analysis on the toxicological effects of Benzo[a]pyrene in pearl oyster Pinctada martensii

Benzo[a]pyrene (BaP) is one of the typical toxic polycyclic aromatic hydrocarbons (PAHs) that are widely present in marine environment. BaP has diverse toxic effects, including teratogenic, carcinogenic, mutagenic effects and so on, in various organisms. In this work, we focused on the differential proteomic and metabolomic responses in the digestive gland of pearl oyster Pinctada martensii exposed to two doses of BaP (1 and 10μg/L). Metabolic responses revealed that the high dose of BaP (10μg/L) mainly caused disturbances in osmotic regulation and energy metabolism in the digestive gland. Proteomic responses indicated that both doses of BaP induced disturbances in energy metabolism, cytoskeleton, cell injury, oxidative stress and signal transduction based on the differential proteomic biomarkers. Overall, these results demonstrated a number of potential biomarkers that were characterized by an integrated proteomic and metabolomic approach and provided a useful insight into the toxicological effects on pearl oyster P. martensii.

Co-expression of heat shock protein (HSP) 40 and HSP70 in Pinctada martensii response to thermal, low salinity and bacterial challenges

Heat shock protein (HSP) 40 proteins are a family of molecular chaperones that bind to HSP70 through their J-domain and regulate the function of HSP70 by stimulating its adenosine triphosphatase activity. In the present study, a HSP40 homolog named PmHSP40 was cloned from the hemocytes of pearl oyster Pinctada martensii using EST and rapid amplification of cDNA ends (RACE) techniques. The full-length cDNA of PmHSP40 was 1251 bp in length, which included a 5' untranslated region (UTR) of 75 bp, an open reading frame (ORF) of a 663 bp, and a 3' UTR of 513 bp. The deduced amino acid sequence of PmHSP40 contains a J domain in the N-terminus. In response to thermal and low salinity stress challenges, the expression of PmHSP40 in hemocytes and the gill were inducible in a time-dependent manner. After bacterial challenge, PmHSP40 transcripts in hemocytes increased and peaked at 6 h post injection. In the gill, PmHSP40 expression increased, similar to expression in hemocytes; however, transcript expression of PmHSP40 was significantly up-regulated at 12 h post injection. Furthermore, the transcripts of PmHSP70 showed similar kinetics as that of PmHSP40, with highest induction during thermal, low salinity stress and bacterial challenges. Altogether these results demonstrate that PmHSP40 is an inducible protein under thermal, low salinity and bacterial challenges, suggesting its involvement in both environmental and biological stresses, and in the innate immunity of the pearl oyster.

miR-29a Participated in Nacre Formation and Immune Response by Targeting Y2R in Pinctada martensii

miR-29a is a conserved miRNA that participates in bone formation and immune response in vertebrates. miR-29a of Pinctada martensii (Pm-miR-29a) was identified in the previous research though deep sequencing. In this report, the precise sequence of mature Pm-miR-29a was validated using miRNA rapid amplification of cDNA ends (miR-RACE) technology. The precursor sequence of Pm-miR-29a was predicted to have 87 bp. Stem loop qRT-PCR analysis showed that Pm-miR-29a was easily detected in all the tissues, although expressions in the mantle and gill were low. The microstructure showed the disrupted growth of the nacre after Pm-miR-29a over-expression, which was induced by mimic injection into P. martensii. Results of the target analysis indicated that neuropeptide Y receptor type 2 (Y2R) was the potential target of Pm-miR-29a. Meanwhile, Pm-miR-29a mimics could obviously inhibit the relative luciferase activity of the reporter containing 3′ UTR (Untranslated Regions) of the Y2R gene. Furthermore, the expression of Y2R was downregulated whereas expressions of interleukin 17 (IL-17) and nuclear factor κB (NF-κB) were upregulated after Pm-miR-29a over-expression in the mantle and gill, thereby suggesting that Pm-miR-29a could activate the immune response of the pearl oyster. Results showed that Pm-miR-29a was involved in nacre formation and immune response by regulating Y2R in pearl oyster P. martensii.

Gene cloning and expression analysis of AhR and CYP4 from Pinctada martensii after exposed to pyrene

Pyrene, a typical polycyclic aromatic hydrocarbon, is a common pollutant in the marine environment. Polycyclic aromatic hydrocarbons initiate cellular detoxification in an exposed organism via the activation of the aryl hydrocarbon receptor (AhR). Subsequent metabolism of these xenobiotics is mainly by the cytochrome P450 enzymes of the phase I detoxification system. Full-length complementary DNA sequences from the pearl oyster Pinctada martensii (pm) encoding AhR and cytochrome P4 were cloned. The P. martensii AhR complementary DNA sequence constitutes an open reading frame that encodes for 848 amino acids. Sequence analysis indicated PmAhR showed high similarity with its homologues of other bivalve species. The cytochrome P(CYP)4 complementary DNA sequence of P. martensii constitutes an open reading frame that encodes for 489 amino acids. Quantitative real-time analysis detected both PmAhR and PmCYP4 messenger RNA expressions in the mantle, gill, hepatapancreas and adductor muscle of P. martensii exposed to pyrene. The highest transcript-band intensities of PmAhR and PmCYP4 were observed in the gill. Temporal expression of PmAhR and PmCYP4 messenger RNAs induction was observed in gills and increased between 3 and 5 days post exposure; then returned to control level. These results suggest that messenger RNAs of PmAhR and PmCYP4 in pearl oysters might be useful parameters for monitoring marine environment pyrene pollution.

MicroRNA, Pm-miR-2305, Participates in Nacre Formation by Targeting Pearlin in Pearl Oyster Pinctada martensii

MicroRNAs (miRNAs) are noncoding RNA molecules that function as negative regulators of target genes. In our previous research, 258 pm-miRNAs were identified in Pinctada martensii by Solexa deep sequencing. Pm-miR-2305 was one of the identified pm-miRNAs with a potential function in biomineralization. In the present study, the precursor of pm-miR-2305 was predicted with 96 bp, containing a characteristic hairpin structure. Stem-loop qRT-PCR analysis indicated that pm-miR-2305 was constitutively expressed in all the tissues (adductor muscle, gill, mantle, hepatopancreas, foot, and gonad) of P. martensii and was highly expressed in the foot. After the over-expression of pm-miR-2305 in the mantle by mimics injection into the muscle of P. martensii, nacre demonstrated disorderly growth, as detected by scanning electron microscopy. Dual luciferase reporter gene assay indicated that pm-miR-2305 mimics could significantly inhibit the luciferase activity of the reporter containing the 3'UTR of the pearlin gene. Western blot analysis demonstrated that the protein expression of pearlin was down-regulated in the mantle tissue after the over-expression of pm-miR-2305. Therefore, our data showed that pm-miR-2305 participated in nacre formation by targeting pearlin in P. martensii.

Computational prediction of candidate miRNAs and their potential functions in biomineralization in pearl oyster Pinctada martensii

MicroRNAs (miRNAs) are a class of non-coding RNA molecules with presumed post-transcriptional regulatory activity in various biological processes, such as development and biomineralization. Pinctada martensii is one of the main species cultured for marine pearl production in China and Japan. In our previous research, 258 pm-miRNAs had been identified by solexa deep sequencing in P. martensii, while it is far from the number of miRNAs found in other species. In this study, based on the transcriptome database of pearl sac, we identified 30 candidate pm-miRNAs by computational prediction. Among the obtained 30 pm-miRNAs, 13 pm-miRNAs were generated from the complementary strand of protein-coding mRNAs, and 17 pm-miRNAs could not be annotated using blastx and tblastn analysis. Notably, 10 of the 30 pm-miRNAs, such as pm-miR-1b, pm-miR-205b and pm-miR-375b, were homologous with the reported pm-miRNAs, respectively. To validate the existence of the identified pm-miRNAs, eight randomly selected pm-miRNAs were tested by stem loop quantitative RT-PCR analyses using 5.8S as the internal reference gene. Target prediction between the obtained pm-miRNAs and biomineralization-related genes by microTar, miRanda and RNA22 indicated pm-miR-2386 and pm-miR-13b may be the key factors in the regulation network by regulating the formation of organic matrix or the differentiation of mineralogenic cell during shell formation. Thus, this study enriched miRNA databases of pearl oyster and provided a new way to understand biomineralization.

Tissue inhibitor of metalloproteinase gene from pearl oyster Pinctada martensii participates in nacre formation

Tissue inhibitors of metalloproteinases (TIMPs) are nature inhibitors of matrix metalloproteinases and play a vital role in the regulation of extracellular matrix turnover, tissue remodeling and bone formation. In this study, the molecular characterization of TIMP and its potential function in nacre formation was described in pearl oyster Pinctada martensii. The cDNA of TIMP gene in P. martensii (Pm-TIMP) was 901 bp long, containing a 5' untranslated region (UTR) of 51 bp, a 3' UTR of 169 bp, and an open reading fragment (ORF) of 681 bp encoding 226 amino acids with an estimated molecular mass of 23.37 kDa and a theoretical isoelectric point of 5.42; The predicted amino acid sequence had a signal peptide, 13 cysteine residues, a N-terminal domain and a C-terminal domain, similar to that from other species. Amino acid multiple alignment showed Pm-TIMP had the highest (41%) identity to that from Crassostrea gigas. Tissue expression analysis indicated Pm-TIMP was highly expressed in nacre formation related-tissues, including mantle and pearl sac. After decreasing Pm-TIMP gene expression by RNA interference (RNAi) technology in the mantle pallium, the inner nacreous layer of the shells showed a disordered growth. These results indicated that the obtained Pm-TIMP in this study participated in nacre formation.