The first high-quality chromosome-level genome of the Sipuncula Sipunculus nudus using HiFi and Hi-C data.

Sipuncula is a class of exocoelomic unsegmented animals whose evolutionary relationships are unresolved. The peanut worm Sipunculus nudus is a globally distributed, economically important species belonging to the class Sipuncula. Herein, we present the first high-quality chromosome-level assembly of S. nudus based on HiFi reads and high-resolution chromosome conformation capture (Hi-C) data. The assembled genome was 1,427 Mb, with a contig N50 length of 29.46 Mb and scaffold N50 length of 80.87 Mb. Approximately 97.91% of the genome sequence was anchored to 17 chromosomes. A BUSCO assessment showed that 97.7% of the expectedly conserved genes were present in the genome assembly. The genome was composed of 47.91% repetitive sequences, and 28,749 protein-coding genes were predicted. A phylogenetic tree demonstrated that Sipuncula belongs to Annelida and diverged from the common ancestor of Polychaeta. The high-quality chromosome-level genome of S. nudus will serve as a valuable reference for studies of the genetic diversity and evolution of Lophotrochozoa.

Genome-wide association study analysis to resolve the key regulatory mechanism of biomineralization in Pinctada fucata martensii.

Biomineralization-controlled exo-/endoskeleton growth contributes to body growth and body size diversity. Molluscan shells undergo ectopic biomineralization to form the exoskeleton and biocalcified "pearl" involved in invading defence. Notably, exo-/endoskeletons have a common ancestral origin, but their regulation and body growth are largely unknown. This study employed the pearl oyster, Pinctada fucata marntensii, a widely used experimental model for biomineralization in invertebrates, to perform whole-genome resequencing of 878 individuals from wild and breeding populations. This study characterized the genetic architecture of biomineralization-controlled growth and ectopic biomineralization. The insulin-like growth factor (IGF) endocrine signal interacted with ancient single-copy transcription factors to form the regulatory network. Moreover, the "cross-phylum" regulation of key long noncoding RNA (lncRNA) in bivalves and mammals indicated the conserved genetic and epigenetic regulation in exo-/endoskeleton growth. Thyroid hormone signal and apoptosis regulation in pearl oysters affected ectopic biomineralization in pearl oyster. These findings provide insights into the mechanism underlying the evolution and regulation of biomineralization in exo-/endoskeleton animals and ectopic biomineralization.

Lipidomic insights into the immune response and pearl formation in transplanted pearl oyster Pinctada fucata martensii.

During pearl culture, the excess immune responses may induce nucleus rejection and death of pearl oysters after transplantation. To better understand the immune response and pearl formation, lipidomic analysis was applied to investigate changes in the serum lipid profile of pearl oyster Pinctada fucata martensii following transplantation. In total, 296 lipid species were identified by absolute quantitation. During wound healing, the content of TG and DG initially increased and then decreased after 3 days of transplantation with no significant differences, while the level of C22:6 decreased significantly on days 1 and 3. In the early stages of transplantation, sphingosine was upregulated, whereas PC and PUFAs were downregulated in transplanted pearl oyster. PI was upregulated during pearl sac development stages. GP and LC-PUFA levels were upregulated during pearl formation stage. In order to identify enriched metabolic pathways, pathway enrichment analysis was conducted. Five metabolic pathways were found significantly enriched, namely glycosylphosphatidylinositol-anchor biosynthesis, glycerophospholipid metabolism, alpha-linolenic acid metabolism, linoleic acid metabolism and arachidonic acid metabolism. Herein, results suggested that the lipids involved in immune response, pearl sac maturation, and pearl formation in the host pearl oyster after transplantation, which might lead to an improvement in the survival rate and pearl quality of transplanted pearl oyster.

Characterization of transcription factor activator pretein-1 (AP-1) and its association with cold tolerance in Pinctada fucata martensii.

AP-1 is an important transcription factor for cell proliferation/differentiation and animal immunity/development; however, its role in research in shellfish is poorly understood. Here, the cDNA of AP-1 gene from Pinctada fucata martensii was characterized. Its expression was detected in all six examined tissues, and a high level was observed in the gill and hepatopancreas. Analysis of the developmental transcriptomes showed that the PmAP-1 gene expression levels were high during D-stage larval and spat stages. The gene also exhibited a significantly high expression under cold tolerance stress. SNP analysis of the exon region and 5' flanking region of PmAP-1 revealed 19 SNPs of which 8 showed significant differences between cold tolerance selection line and base stock. Furthermore, three haplotypes generated by the SNPs of PmAP-1 were significantly associated with cold tolerance, respectively.These results suggest that the PmAP-1 gene plays an important role in the response of P. f. martensii to low temperature stress. These SNPs and haplotypes of PmAP-1 may be related to the cold tolerance of P. f. martensii, and could be candidate markers potentially for further selective breeding.

Integrated GC-MS- and LC-MS-Based Untargeted Metabolomics Studies of the Effect of Vitamin D3 on Pearl Production Traits in Pearl Oyster Pinctada fucata martensii.

Pearl oyster Pinctada fucata martensii is widely recognized for biomineralization and has been cultured for high-quality marine pearl production. To ascertain how dietary vitamin D3 (VD3) levels affect the features of pearl production by P. f. martensii and discover the mechanisms regulating this occurrence, five experimental diets with variable levels of VD3 were used with inclusion levels of 0, 500, 1,000, 3,000, and 10,000 IU/kg. The distinct inclusion levels were distributed into five experimental groups (EG1, EG2, EG3, EG4, and EG5). All the experimental groups were reared indoors except the control group (CG) reared at the sea. Pearl oysters, one year and a half old, were used in the grafting operation to culture pearls. During the growing period that lasted 137 days, EG3 had the highest survival rate, retention rate, and high-quality pearl rate. A similar trend was found for EG3 and CG with significantly higher pearl thickness and nacre deposition rates than other groups, but no significant differences were observed between them. A metabolomics profiling using GC-MS and LC-MS of pearl oysters fed with low quantities of dietary VD3 and optimal levels of dietary VD3 revealed 135 statistically differential metabolites (SDMs) (VIP > 1 and p < 0.05). Pathway analysis indicated that SDMs were involved in 32 pathways, such as phenylalanine metabolism, histidine metabolism, glycerophospholipid metabolism, alanine aspartate and glutamate metabolism, arginine and proline metabolism, glycerolipid metabolism, amino sugar and nucleotide sugar metabolism, and tyrosine metabolism. These results provide a theoretical foundation for understanding the impacts of VD3 on pearl production traits in pearl oyster and reinforce forthcoming prospects and application of VD3 in pearl oyster in aquaculture rearing conditions.

Identification and Allelic Variants Associated With Cold Tolerance of PmPIAS in Pinctada fucata martensii.

The protein inhibitor of activated STAT (PIAS) functions in diverse aspects, including immune response, cell apoptosis, cell differentiation, and proliferation. In the present study, the PIAS in the pearl oyster Pinctada fucata martensii was characterized. The sequence features of PmPIAS were similar to that of other PIAS sequences with PIAS typical domains, including SAP, Pro-Ile-Asn-Ile-Thr (PINIT), RLD domain, AD, and S/T-rich region. Homologous analysis showed that PmPIAS protein sequence showed the conserved primary structure compared with other species. Ribbon representation of PIAS protein sequences also showed a conserved structure among species, and the PINIT domain and RLD domain showed the conserved structure compared with the sequence of Homo sapiens. The expression pattern of PmPIAS in different tissues showed significant high expression in the gonad. PmPIAS also exhibited a significantly higher expression in the 1 and 2 days after cold tolerance stress (17°C) and showed its potential in the cold tolerance. The SNP analysis of the exon region of PmPIAS obtained 18 SNPs, and among them, 11 SNPs showed significance among different genotypes and alleles between cold tolerance selection line and base stock, which showed their potential in the breeding for cold tolerance traits.

Novel nicotinic acetylcholine receptor involved in immune regulation in pearl oyster (Pinctada fucata martensii).

The cholinergic anti-inflammatory pathway has been identified as a reflex monitoring system that contributes to the physiological and pathological regulation of cytokines. Nicotinic acetylcholine receptor (nAChR) plays an important role in immune regulation as a key molecule in neuronal communication. In this work, we investigated the characteristics and functions of a novel nAChR ß gene identified from the pearl oyster Pinctada fucata martensii (PmnAChR-ß). PmnAChR-ß displays structural similarities to nAChR molecules described in mammals, including a typical neurotransmitter-gated ion-channel ligand binding domain (LBD) and transmembrane (TM) domain. The result of phylogenetic analysis speculated that nAChR-ß in Mollusca, Chordata and Arthropoda were separated into three branches. The LBD of PmnAChR-ß was highly conserved, but its TM was variable. PmnAChR-ß was highly expressed in eggs and fertilized eggs and had the most abundant mRNA expression in the gills of pearl oyster. The expression of PmnAChR-ß mRNA was dramatically upregulated 12 h after lipopolysaccharide stimulation. Furthermore, PmnAChR-ß was highly expressed at 12 h and 6-18 d after transplantation in hemocytes. Pm-miR-516b-5p was identified as the regulatory microRNA of PmnAChR-ß. These results indicated that PmnAChR-ß may be an important component of the cholinergic anti-inflammatory pathway and participates in the immune regulation process of pearl oysters.

LncMSEN1, a mantle-specific LncRNA participating in nacre formation and response to polyI:C stimulation in pearl oyster Pinctada fucata martensii.

Long noncoding RNA (LncRNA) regulates various life processes, including biomineralization and innate immune response through complex mechanisms. In this research, we identified a LncRNA named LncMSEN1 from pearl oyster Pinctada fucata martensii. LncMSEN1 sequence was validated by PCR, and its expression was high in mantle tissues according to qRT-PCR. LncMSEN1 was co-located with the nacre matrix protein N-U8 and fibrinogen domain-containing protein. And LncMSEN1 and N-U8 expression levels in the mantle were positively correlated. RNA interference was used to detect its effect on nacre formation in shells. Results showed that the decreased LncMSEN1 expression in mantle can cause the disordered growth of crystals on the inner surface of nacre in the shells, as well as the decrease expression of N-U8. In addition, the LncMSEN1 expression level significantly increased at 24 h after polyI:C stimulation in the mantle (P < 0.05). These findings suggested the involvement of LncMSEN1 in the formation of nacre in shells and related to innate immune response in pearl oyster, which provided additional insights into the roles of LncRNAs in pearl oysters.

Effect of vitamin D3 on immunity and antioxidant capacity of pearl oyster Pinctada fucata martensii after transplantation: Insights from LC-MS-based metabolomics analysis.

Postoperative care is a critical step of pearl culture that ultimately determines culture success. To determine the effect of dietary vitamin D3 (VD3) levels on immunity and antioxidant capacity of pearl oyster Pinctada fucata martensii during postoperative care and explore the mechanisms behind this phenomenon, five isonitrogenous and isolipidic experimental diets were formulated by adding different levels of dietary VD3 (0, 500, 1000, 3000, and 10000 IU/kg), and the diets were fed to five experimental groups (EG1, EG2, EG3, EG4, and EG5) in turn and cultured indoors. The control group (CG) was cultured in the natural sea. Pearl oysters that were 1.5 years old were subjected to nucleus insertion. After culturing for 30 days, EG3 exhibited significantly higher survival rates than those in CG and EG5 (P < 0.05). Moreover, EG3 exhibited the highest activities of alkaline phosphatase, acid phosphatase, catalase, superoxide dismutase, and lysozyme. However, EG5 achieved the highest activities of glutathione peroxidase. Metabolomics-based profiling of pearl oysters fed with high levels of dietary VD3 (EG5) and optimum levels of dietary VD3 (EG3) revealed 76 significantly differential metabolites (SDMs) (VIP > 1 and P < 0.05). Pathway analysis indicated that SDMs were involved in 21 pathways. Furthermore, integrated key metabolic pathway analysis suggested that pearl oysters in EG5 regulated the pentose phosphate pathway, glutathione metabolism, sphingolipid metabolism, and arachidonic acid metabolism in response to stress generated from excessive VD3. These findings had significant implications on strengthening the future development and application of VD3 in aquaculture of pearl oyster P. f. martensii.

HSP40 gene family in pearl oyster Pinctada fucata martensii: Genome-Wide identification and function analysis.

HSP40, also called DnaJ, functions as a molecular chaperone by binding to Hsp70 and plays critical roles in the growth, development, and response to heat stress. However, this gene family is rarely reported in pearl oyster. In this study, 31 putative HSP40 genes from Pinctada fucata martensii (PmHSP40) were identified through bioinformatics methods and classified into three groups according to the presence of the complete three domains (J, G/F zinc finger domain, and cysteine rich domain). Further analysis showed that the PmHSP40 genes are highly diverse in sequence, domain structure, and tissue and development expression profile, implying diversified functions. In addition, one highly induced PmHSP40 in low-temperature (PmHSP40LT) was cloned, and its function in temperature response was explored. PmHSP40LT has a full length of 1741 bp, containing 1059 bp ORF, 152 bp 5'UTR, and a 507 bp 3'UTR, and encodes 352 amino acids. PmHSP40LT expression was significantly induced at low (17 °C) and high temperature (32 °C) at 6 h, 1 d, and 3 d relative to the control group. Thus, PmHSP40LT possibly participates in response to high and low temperatures in pearl oyster. In conclusion, all these results provide a comprehensive basis for the further analysis of PmHSP40 function in pearl oysters.

Comprehensive transcriptome analysis reveal key molecular events in the pearl oyster after pre-grafting conditioning.

Pre-grafting conditioning is a crucial procedure before transplant surgery during pearl production. To investigate the molecular response of the pearl oyster Pinctada fucata martensii to conditioning, we constructed two hemocyte transcriptomes from pearl oysters with and without conditioning. A total of 134,222,686 raw reads were generated and assembled using the reference genome of the pearl oyster. Transcriptome analysis revealed 3,074 differentially expressed genes (DEGs). Gene ontology and pathway enrichment analyses revealed that these DEGs were mainly associated with "microtubule-based process", "regulation of actin cytoskeleton", and "cell cycle". All related genes were over-expressed in pearl oysters after conditioning. Some nucleotide-binding oligomerization domain-like receptors (NLR), toll-like receptor, myd88, proinflammatory cytokine interleukin-17 (IL-17), and apoptosis-related genes were highly expressed in pearl oysters after conditioning, indicating that conditioning induced the immune response of pearl oysters. "Fatty acid biosynthesis" (FA biosynthesis) was included in the enriched terms, and all eight FA synthase genes in this pathway were highly induced after conditioning. Four tandemly duplicated arginine kinase genes (PmAK) were found in the genome of P. f. martensii, gene structure and sequence analysis indicated PmAK genes were more diverse compared with that from human and zebra fish. The four tandemly duplicated PmAKs were highly up-regulated after conditioning. These findings will help to elucidate the responding molecular events after conditioning and explain the high pearl oyster survival rate with conditioning after transplantation, thereby providing useful information in perfecting the conditioning method to improve pearl oyster survival rate after transplantation.

Genome and transcriptome analyses providing insight into the immune response of pearl oysters after allograft and xenograft transplantations.

The immune response after allograft or xenograft transplantation in the pearl oyster is a major factor that cause its nucleus rejection and death. To determine the mechanism underlying the immune response after allograft and xenograft transplantations in the pearl oyster Pinctada fucata martensii, we constructed two sets of transcriptomes of hemocytes at different times (6 and 12 h; 1, 3, 6, 12, and 30 d) after allograft and xenograft transplantations, in which the xenografted mantle tissue was from Pinctada maxima. The transcriptomic analysis reveals many genes are involved in the immune response to transplantation, such as transient receptor potential cation channel (TRP), calmodulin (CaM), DNA replication-related genes, and sugar and lipid metabolism-related genes. The expression of these identified genes was higher in the host pearl oyster transplanted with xenograft than that by allograft. The histological analysis of the pearl sac also confirmed that many hemocytes were still gathered around the transplanted nucleus, and no pearl sac was formed in the host pearl oysters at 30 d after xenograft transplantation. The genomic analysis indicated that pearl oysters evolved many copies of genes, such as TRP, CaM, and GST, to sense and cope with the immune response after transplantation. "Ribosome" and "Cytosolic DNA-sensing pathway" were specifically induced in the xenograft group, whereas "Notch signaling pathway" specifically responded to the allograft transplantation. These results can improve our understanding of the mechanism underlying the immune response of pearl oysters after allograft and xenograft transplantations.

Evolution and function analysis of interleukin-17 gene from Pinctada fucata martensii.

Interleukin-17 (IL-17) is a proinflammatory cytokine that plays an important role in immune responses. In this study, we identified 57 IL-17 genes from the genomes of six marine invertebrates, including Pinctada fucata martensii, Crassostrea gigas, Lottia gigantea, Capitella teleta, Mizuhopecten yessoensis, and Mytilus galloprovincialis. Phylogenetic analysis showed that all invertebrate IL-17 genes were clustered into one group, implying that invertebrate IL-17 evolved from one common ancestral gene. From the extron-intron analysis, we found many intronless IL-17 genes in mollusks, which may be caused by retroposition. Tissue and development transcriptomic analysis showed that the expression of PmIL-17 was tissue and developmental stage-specific. Moreover, we cloned the full length of the IL-17-2 gene from P. f. martensii (PmIL-17-2) and explored its function in the immune response. The full-length cDNA of PmIL-17-2 is 719 bp, containing an open reading frame of 564 bp, a 5' -untranslated region (UTR) of 31 bp, and a 3' -UTR of 124 bp with a 30 bp poly (A) tail. PmIL-17-2 had a strong response to lipopolysaccharide (LPS), indicating that the PmIL-17-2 participates in innate immune responses. In situ hybridization of hemocytes showed that PmIL-17-2 was mainly produced by granulosa cells, and the number of the stained granulosa increased after LPS stimulation. These results lay the foundation for the research of IL-17 family in marine invertebrates.

Integrated application of transcriptomics and metabolomics provides insights into unsynchronized growth in pearl oyster Pinctada fucata martensii.

Similar to other marine bivalves, Pinctada fucata martensii presents unsynchronized growth, which is one of the problems farmers currently face. However, the underlying mechanisms have not been studied. In the present study, pearl oyster P. f. martensii from cultured stocks were selected to produce a progeny stock. At 180 days, the stock was sorted by size, and fast- and slow-growing individuals were separately sampled. Then, metabolomic and transcriptomic approaches were applied to assess the metabolic and transcript changes between the fast- and slow-growing P. f. martensii groups and understand the mechanism underlying their unsynchronized growth. In the metabolomics assay, 30 metabolites were considered significantly different metabolites (SDMs) between the fast- and slow-growing groups and pathway analysis indicated that these SDMs were involved in 20 pathways, including glutathione metabolism; sulfur metabolism; valine, leucine, and isoleucine biosynthesis; and tryptophan metabolism. The transcriptome analysis of different growth groups showed 168 differentially expressed genes (DEGs) and pathway enrichment analysis indicated that DEGs were involved in extracellular matrix-receptor interaction, pentose phosphate pathway, aromatic compound degradation. Integrated transcriptome and metabolome analyses showed that fast-growing individuals exhibited higher biomineralization activity than the slow-growing group, which consumed more energy than the fast-growing group in response to environmental stress. Fast-growing group also exhibited higher digestion, anabolic ability, and osmotic regulation ability than the slow-growing group. This study is the first work involving the integrated metabolomic and transcriptomic analyses to identify the key pathways to understand the molecular and metabolic mechanisms underlying unsynchronized bivalve growth.

Response to different dietary carbohydrate and protein levels of pearl oysters (Pinctada fucata martensii) as revealed by GC-TOF/MS-based metabolomics.

Land-based culturing can avoid the effects of environmental pollution and natural disasters, thus ensuring food safety for shellfish. However, food availability, in this case, is limited. To achieve the optimum balance of dietary carbohydrates and proteins and explore the mechanisms behind the phenomenon, we formulated five isoenergetic and isolipidic diets (C30P40, C35P35, C40P30, C45P25, and C50P20) with different levels of carbohydrates (C) and proteins (P). There were five experimental groups (C30P40, C35P35, C40P30, C45P25, and C50P20) and two control groups (CG1 and CG2). CG1 was fed with mixed powders of yeast and Chlorella sp., and CG2 was cultured in natural sea. After 60-day feeding, the highest rates of survival and absolute growth appeared in C45P25. C45P25 exhibited significantly higher activities of amylase, protease, alkaline phosphatase, acid phosphatase, superoxide dismutase, catalase, glutathione peroxidase, and phenoloxidase and significantly lower malondialdehyde content than C30P40, C35P35, C40P30, C50P20, and CG1. No significant differences were observed between C45P25 and CG2. Furthermore, the total antioxidant capacity of the pearl oysters in C45P25 was significantly higher than that in C30P40, C35P35, C40P30, and C50P20. On the basis of these results, the optimal balance of proteins and carbohydrates for pearl oysters was the C45P25 diet. Metabolomics-based profiling of the pearl oysters fed with high-carbohydrate/low-protein diet (C45P25) and low-carbohydrate/high-protein diet (C30P40) revealed 80 significantly different metabolites (VIP > 1 and P < 0.05). Furthermore, integrated key metabolic pathway analysis showed that C45P25 regulated starch and sucrose metabolism, alanine, aspartate and glutamate metabolism and glycine, serine and threonine metabolism to meet the energy demand and increase the glucogenic amino acid, thereby promoting protein synthesis and reducing fatty acid ß-oxidation in comparison with C30P40. This finding helps elucidate the underlying mechanisms leading to the high-carbohydrate/low-protein diet characteristic of the optimal dietary carbohydrate and protein levels of P. f. martensii.

Metabolomics Responses of Pearl Oysters (Pinctada fucata martensii) Fed a Formulated Diet Indoors and Cultured With Natural Diet Outdoors.

Natural disasters and environmental pollution are the main problems in traditional offshore cultivation. While culturing pearl oysters through industrial farming can avoid these problems, food availability in this case is limited. This study compares the metabolomics responses of pearl oysters, Pinctada fucata martensii, fed a formulated diet indoors with those of oysters cultured with natural diet outdoors by using a gas chromatography time-of-flight mass spectrometry (GC-TOF/MS)-based metabolomics approach. The animals were divided into two groups as follows: the experimental group (EG) was fed a formulated diet indoors and the control group (CG) was cultured with natural diet outdoors. After 45 days of feeding, the survival rate of EG was significantly higher than that of CG. The absolute growth rate (AGR) of the total weight of EG did not significantly differ from that of CG, but the AGRs of the shell length, shell height, and shell width of CG were significantly higher than those of EG. EG showed significantly higher amylase activities than CG, and the hexokinase and glucose-6-phosphate isomerase concentrations of the former were significantly lower than those of the latter. Metabolomics revealed 125 metabolites via mass spectrum matching with a spectral similarity value > 700 in the hepatopancreas, and 48 metabolites were considered to be significantly different between groups (VIP > 1 and P < 0.05). Pathway analysis results indicated that these significantly different metabolites were involved in 34 pathways. Further integrated key metabolic pathway analysis showed that, compared with CG, EG had lower capabilities for cysteine and methionine metabolism, sulfur metabolism, and starch and sucrose metabolism. This study demonstrated that the formulated diet could be an excellent substitute for natural diet; however, its nutrients were insufficient. Effective strategies should be developed to enhance the utilization of formulated diets.

Molecular and functional analysis of PmCHST1b in nacre formation of Pinctada fucata martensii.

Keratan sulfate possesses considerable amounts of negatively charged sulfonic acid groups and participates in biomineralization. In the present study, we investigated characteristics and functions of a CHST1 gene identified from the pearl oyster Pinctada fucata martensii (PmCHST1b) which participated in the synthesis of keratan sulfate. PmCHST1b amino acid sequence carried a typical sulfotransferase-3 domain (sulfotransfer-3 domain) and belonged to membrane-associated sulfotransferases. Homologous analysis of CHST1 from different species showed the conserved motif (5' PSB motif and 3' PB motif) which interacted with 3'-phosphoadenosine-5'-phosphosulfate (PAPS). Structure analysis of sulfotransferase domain indicted that PmCHST1b showed the conserved catalytic structure character and the relationships presented in the phylogenetic tree conformed to that of traditional taxonomy. Expression pattern of PmCHST1b in different tissues and development stages showed that PmCHST1b widely expressed in all the detected tissues and development stages and showed the highest expression level in the central zone of mantle (MC). PmCHST1b expressed highly in the trochophore, D-stage larvae and spat which corresponded to prodissoconch and dissoconch shell formation, respectively. RNA interference (RNAi) successfully inhibited expression level of PmCHST1b in MC (P<0.05), and sulfate polymer content in the extrapallial fluid significantly reduced (P<0.05). Crystallization of shell nacre became irregular. Results above indicated that PmCHST1b may affect nacre formation by participating in synthesis of keratan sulfate in extrapallial fluid. This study provided fundamental materials for further research on the role of sulfotransferases and keratan sulfate in nacre formation.

Molecular cloning and characteristics analysis of Pmtgfbr1 from Pinctada fucata martensii.

Pinctada fucata martensii is cultured for pearl production. Growth improvement has received considerable research interest. Transforming growth factor ß type Ⅰ receptor (TßR-I), which is involved in signals transmission of transforming growth factor beta (TGF-ß), participates in cell proliferation and growth. In this study, we characterized a Tgfbr1 gene which encoded TßR-I from P. fucata martensii (Pmtgfbr1). Pmtgfbr1 cDNA contains an open reading frame of 1569 bp and encodes a polypeptide of 522 amino acids (aa). Pmtgfbr1 possesses a typical TßR-I structure (extracellular receptor ligand domain, transmembrane domain, and cytoplasmic tyrosine kinase catalytic domain). Pmtgfbr1 is expressed in all the studied tissues and exhibited the highest expression level in the adductor muscle. Moreover, Pmtgfbr1 exhibited the lower expression level in the larger group (L) than that in the smaller group (S) and is negatively correlated with growth traits (P < 0.01). Our results indicated that Pmtgfbr1 is a candidate functional gene associated with growth traits.

Identification of EGFR in pearl oyster (Pinctada fucata martensii) and correlation analysis of its expression and growth traits.

Marine pearl production is directly influenced by the growth speed of Pinctada fucata martensii. However, the slow growth rate of this organism remains the main challenge in aquaculture production. Epidermal growth factor receptor (EGFR), an important receptor of tyrosine kinases in animals, plays versatile functions in development, growth and tissue regeneration. In this study, we described the characteristic and function of an EGFR gene identified from P. f. martensii (PmEGFR). PmEGFR possesses a typical EGFR structure and is expressed in all studied tissues, with the highest expression level in adductor muscle. PmEGFR expression level is significantly higher in the fast-growing group than that in the slow-growing one. Correlation analysis represents that shell height and shell weight show positive correlation with PmEGFR expression (p < 0.05), and total weight and tissue weight exhibit positive correlation with it (p < 0.01). This study indicates that PmEGFR is a valuable functional gene associated with growth traits.