Somatostatin Receptor Gene Functions in Growth Regulation in Bivalve Scallop and Clam.

Bivalves hold an important role in marine aquaculture and the identification of growth-related genes in bivalves could contribute to a better understanding of the mechanism governing their growth, which may benefit high-yielding bivalve breeding. Somatostatin receptor (SSTR) is a conserved negative regulator of growth in vertebrates. Although SSTR genes have been identified in invertebrates, their involvement in growth regulation remains unclear. Here, we identified seven SSTRs (PySSTRs) in the Yesso scallop, Patinopecten yessoensis, which is an economically important bivalve cultured in East Asia. Among the three PySSTRs (PySSTR-1, -2, and -3) expressed in adult tissues, PySSTR-1 showed significantly lower expression in fast-growing scallops than in slow-growing scallops. Then, the function of this gene in growth regulation was evaluated in dwarf surf clams (Mulinia lateralis), a potential model bivalve cultured in the lab, via RNA interference (RNAi) through feeding the clams Escherichia coli containing plasmids expressing double-stranded RNAs (dsRNAs) targeting MlSSTR-1. Suppressing the expression of MlSSTR-1, the homolog of PySSTR-1 in M. lateralis, resulted in a significant increase in shell length, shell width, shell height, soft tissue weight, and muscle weight by 20%, 22%, 20%, 79%, and 92%, respectively. A transcriptome analysis indicated that the up-regulated genes after MlSSTR-1 expression inhibition were significantly enriched in the fat digestion and absorption pathway and the insulin pathway. In summary, we systemically identified the SSTR genes in P. yessoensis and revealed the growth-inhibitory role of SSTR-1 in bivalves. This study indicates the conserved function of somatostatin signaling in growth regulation, and ingesting dsRNA-expressing bacteria is a useful way to verify gene function in bivalves. SSTR-1 is a candidate target for gene editing in bivalves to promote growth and could be used in the breeding of fast-growing bivalves.

A Systematical Survey on the TRP Channels Provides New Insight into Its Functional Diversity in Zhikong Scallop (Chlamys farreri).

Transient receptor potential (TRP) channel plays a significant role in mediating various sensory physiological functions. It is widely present in the vertebrate and invertebrate genomes and can be activated by multiple compounds, messenger molecules, temperature, and mechanical stimulation. Mollusks are the second largest phylum of the animal kingdom and are sensitive to environmental factors. However, the molecular underpinnings through which mollusks sense and respond to environmental stimulus are unknown. In this study, we systematically identified and characterized 17 TRP channels (C.FA TRPs, seven subfamilies) in the genome of the Zhikong scallop (Chlamys farreri). All C.FA TRPs had six transmembrane structures (TM1-TM6). The sequences and structural features of C.FA TRPs are highly conserved with TRP channels of other species. Spatiotemporal expression profiling suggested that some C.FA TRPs participated in the early embryonic development of scallops and the sensory process of adult tissues. Notably, the expression of C.FA TRPM3 continuously increased during developmental stages and was highest among all C.FA TRPs. C.FA TRPC-α was specifically expressed in eyes, which may be involved in light transmission of scallop eyes. Under high temperature stress, C.FA TRPA1 and C.FA TRPA1-homolog upregulated significantly, which indicated that the TRPA subfamily is the thermoTRPs channel of scallops. Our results provided the first systematic study of TRP channels in scallops, and the findings will provide a valuable resource for a better understanding of TRP evolution and function in mollusks.

Identification and functional analysis of a sex-biased transcriptional factor Foxl2 in the bay scallop Argopecten irradians irradians.

Transcription factor Foxl2 is an evolutionarily conserved gene playing pivotal roles in regulation of early ovarian differentiation and maintenance in animals. However, the Foxl2 gene has not been thoroughly studied in hermaphroditic scallops. In this study, we cloned and characterized a Foxl2 (designated as AiFoxl2) from the bay scallop Argopecten irradians irradians. The open reading frame of AiFoxl2 was 1122 bp encoding 373 amino acids residues and contained a conserved forkhead box domain. Quantitative real-time PCR showed that AiFoxl2 was mainly expressed in the ovary. Moreover, the highest expression of AiFoxl2 in the ovary was detected at proliferative stage and growing stage, while the lowest level was found at resting stage. During the embryonic and larval development, expression of AiFoxl2 was found first in fertilized eggs, increased significantly at the blastula stage, and reached peak value at the D-larvae stage. When AiFoxl2 was knocked down, testis development-related genes (Dmrt1, Sox7 and Sox9) were up-regulated significantly while the ovary development-related genes (Vg, HSD14, and GATA-1) were down-regulated manifestly. These findings suggested that AiFoxl2 was a female-related gene in A. i. irradians and may be involved in regulation of ovarian development and differentiation.

Gonadal somatic cell-specific transforming growth factor-ß superfamily member in the Yesso scallop reveals gonadal somatic cell distribution during the reproductive phase.

The objective of this study was to identify the gonadal somatic cells in the Yesso scallop using a novel molecular marker. This study is the first to identify the bone morphogenetic protein 2a (Bmp2a) gene as a gonadal somatic cell-specific gene in this bivalve. We performed a transcriptomic survey to identify the transforming growth factor-ß (TGFß) superfamily members that act in Yesso scallop gonad development. BLAST survey, phylogenetic tree, and RT-PCR analyses screened BMP molecules (i.e., bmp2a and bmp10a), which are members of the TGFß superfamily that show gonad-specific expression. Among the BMPs from the Yesso scallop, in situ hybridization accompanied by RNAscope assay identified that bmp2a mRNA was specifically expressed in the gonadal somatic cells localized in the interspace between germ cells. Real-time quantitative PCR (qPCR) analysis revealed that bmp2a mRNA expression increased during the reproductive phase. The relative expression of bmp2a mRNA was lowest at the beginning of the growing stage and peaked at the mature stage in both sexes. These observations indicate that bmp2a-positive gonadal somatic cells support germ cell growth and differentiation during the reproductive phase for both sexes. This study provides new insights into gonadal somatic cell biology in marine invertebrates and we propose that TGFß signaling is necessary for gonad development in bivalves.

Characterizing transcriptome in female scallop Chlamys farreri provides new insights into the molecular mechanisms of reproductive regulation during ovarian development and spawn.

Bivalve mollusks are descendants of an early-Cambrian lineage and have successfully evolved unique strategies for reproduction. Nonetheless, the molecular mechanisms underlying reproductive regulation in mollusks remain to be elucidated. In this study, transcriptomes of ovary at four reproductive stages in female Chlamys farreri were characterized by RNA-Seq. Regarding signaling pathways, ECM-receptor interaction pathway, mTOR signaling pathway, Fanconi anemia pathway, FoxO signaling pathway, Wnt signaling pathway and Hedgehog signaling pathway were enriched during ovarian development processes. In addition, pathways related to energy metabolism such as Nitrogen metabolism and Arachidonic acid metabolism were enriched at spawn stage. Interestingly, Neuroactive ligand-receptor interaction was significantly enriched involved in ovarian development and spawn, and indicated the potential functions of nervous system on reproductive regulation in C. farreri. What's more, this study identified and characterized fourteen genes involved in "sex hormones synthesis and regulation", "ovarian development and spawn" and "maternal immunity" during the four reproductive stages in C. farreri. We determined that CYP17 uniquely affected gamete release by influencing the physiological balance among the steroid hormones and showed that receptors of the 5-HT and GABA neurotransmitters were tightly associated with ovarian maturation. Furthermore, to the best of our knowledge, this is the first study to report the maternal effect gene Zar1 in bivalve mollusks, likewise the maternal immunity genes displayed coordinated and cooperative expression during reproductive periods, which strengthened the environmental adaptation mechanisms of bivalves. Taken together, this study provides the first dynamic transcriptomic analysis of C. farreri at four key reproductive stages, which will assist in revealing the molecular mechanisms underlying bivalves on reproductive regulation in ovarian development and spawn.

Exposure of bay scallop Argopecten irradians to micro-polystyrene: Bioaccumulation and toxicity.

Marine microplastic pollution poses a threat to aquatic organisms, including bivalves. In this study, we investigated the accumulation of microplastics and their elicited antioxidant stress response in the bay scallop Argopecten irradians. Scallops were exposed to 1 µm diameter micro-polystyrene (MP) beads at 10, 100, and 1000 beads/mL concentrations for a 7 day period. Bead presence in the digestive diverticula and defense responses in the digestive diverticula and hemolymph were measured at 1, 3, 5, and 7 days. The activity and expression of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) and H2O2 in the digestive diverticula and/or hemolymph of scallops increased with microplastic concentration and exposure duration. These results suggest that microplastics can accumulate in the digestive diverticula of A. irradians, and that exposure to microplastics induces oxidative stress in bivalves. It is likely that exposure to high concentrations of micro- or nano-sized plastic particles could potentially have adverse effects in bivalves.

Expression profiling of the Kdm genes in scallop Patinopecten yessoensis suggests involvement of histone demethylation in regulation of early development and gametogenesis.

Histone demethylation modification is an important means of gene expression regulation and is widely involved in biological processes such as animal reproduction and development. Histone lysine demethylases (Kdm) plays an important role in the demethylation of histones. To understand the role of histone demethylation in scallops, we identified the Kdm gene family of the Yesso scallop Patinopecten yessoensis, and analyzed its expression during the gonad and early development. The results showed that the P. yessoensis has a complete Kdm family including seventeen members that belong to sixteen subfamilies (Hif1an, Hspbap1, Jarid2, Jmjd4, Jmjd6, Jmjd7, Jmjd8, Kdm1, Kdm2, Kdm3, Kdm4, Kdm5, Kdm6, Kdm7, Kdm8 and Kdm9). The Kdm genes showed five different expression patterns in the early development of scallop, with some of them (e.g. Jmjd7, Jmjd8 and Kdm8) being highly expressed in only one or two stage and the others (e.g. Kdm1A, Kdm9, Jmjd4 and Jmjd6) in several consecutive stages. During gonadal development, the Kdm genes also display various expression patterns. Some genes (e.g. Kdm2, Kdm4 and Jmjd7) display preferential expression in the testis, and the others have no obvious sex bias but show stage preference (resting, proliferative, growing or maturation stage). These results suggest that various histone demethylation modifications (e.g. H3K4, H3K9 and H3K27) may participate in the regulation of gametogenesis and early development of Yesso scallop. It will facilitate a better understanding of the epigenetic contributions to mollusk development.

Identification and expression profiles of Fox transcription factors in the Yesso scallop (Patinopecten yessoensis).

The forkhead box (Fox) gene family is a family of transcription factors that play important roles in a variety of biological processes in vertebrates, including early development and cell proliferation and differentiation. However, at present, studies on the mollusk Fox family are relatively lacking. In the present study, the Fox gene family of the Yesso scallop (Patinopecten yessoensis) was systematically identified. In addition, the expression profiles of the Fox gene family in early development and adult tissues were analyzed. The results showed that there were 26 Fox genes in P. yessoensis. Of the 26 genes, 24 belonged to 20 subfamilies. The Fox genes belonging to the I, Q1, R and S subfamilies were absent in P. yessoensis. The other 2 genes formed 2 independent clades with the Fox genes of other mollusks and protostomes. They might be new members of the Fox family and were named FoxY and FoxZ. P. yessoensis contained a FoxC-FoxL1 gene cluster similar in structure to that of Branchiostoma floridae, suggesting that the cluster might already exist in the ancestors of bilaterally symmetrical animals. The gene expression analysis of Fox showed that most of the genes were continuously expressed in multiple stages of early development, suggesting that Fox genes might be widely involved in the regulation of embryo and larval development of P. yessoensis. Nine Fox genes were specifically expressed in certain tissues, such as the nerve ganglia, foot, ovary, testis, and gills. For the 9 genes that were differentially expressed between the testis and ovary, their expression levels were analyzed during the 4 developmental stages of gonads. The results showed that FoxL2, FoxE and FoxY were highly expressed in the ovary during all developmental stages, while FoxZ was highly expressed in the testis during all developmental stages. The results suggested that these genes might play an important role in sex maintenance or gametogenesis. The present study could provide a reference for evolutionary and functional studies of the Fox family in metazoans.

Integrated transcriptomic and proteomic analyses of the tissues from the digestive gland of Chlamys farreri following cadmium exposure.

OBJECTIVES: Cadmium causes the pollution of marine habitat and Chlamys farreri is an effective concentrator of heavy metals, the aim of this study was to study the response mechanism of C. farreri to cadmium stress at transcriptomic and proteomic levels. METHODS: Transcriptomic analysis based on RNA-sequencing and proteomic analysis based on isobaric tags for relative and absolute quantitation were performed to reveal the molecular response of C. farreri to different concentrations of cadmium (0.1, 0.3, and 1 mg/L). In addition, a protein-protein interaction (PPI) network was constructed based on the Cytoscape tool to identify hub proteins related to the response of C. farreri to cadmium stress. RESULTS: A total of 24 190 unigenes from 58 683 candidates were annotated in known databases. The numbers of the differentially expressed unigenes (DEGs) was different among the three cadmium-treated groups compared with the control group. DEGs were involved in many pathways such as ABC transporters, protein processing in endoplasmic reticulum and endocytosis. A total of 660 proteins were identified, and differentially expressed proteins (DEPs) among different groups were determined. The overlapping DEGs and DEPs were associated with cadmium response. The upregulated unigene0002618 and downregulated unigene0000904 may be more important for the response of C. farreri to cadmium stress. Unigene0009750 was the hub protein in the PPI network with the highest degree of 20. CONCLUSIONS: Our transcriptomic and proteomic analyses elucidated the molecular response of C. farreri to cadmium stress.

Histological and Expression Differences Among Different Mantle Regions of the Yesso Scallop (Patinopecten yessoensis) Provide Insights into the Molecular Mechanisms of Biomineralization and Pigmentation.

The molecular mechanisms of shell formation and pigmentation are issues of great interest in molluscan studies due to the unique physical and biological properties of shells. The Yesso scallop, Patinopecten yessoensis, is one of the most important maricultural bivalves in Asian countries, and its shell color shows polymorphism. To gain more information about the underlying mechanisms of shell formation and pigmentation, this study presents the first analyses of histological and transcriptional differences between different mantle regions of the Yesso scallop, which are thought to be responsible for the formation of different shell layers. The results showed major microstructural differences between the edge and central mantles, which were closely associated with their functions. Different biomineralization-related GO functions, which might participate in the formation of different shell layers, were significantly enriched in the different mantle regions, indicating the different molecular functions of the two mantle regions in shell formation. The melanogenesis pathway, which controls melanin biosynthesis, was the most significantly enriched pathway in the DEGs between the two mantle regions, indicating its important role in shell pigmentation. Tyr, the key and rate-limiting gene in melanogenesis, was expressed at a remarkably high level in the central mantle, while the upstream regulatory genes included in melanogenesis were mainly upregulated in the edge mantle, suggesting the different molecular functions of the two mantle regions in shell pigmentation.

Diverse expression regulation of Hsp70 genes in scallops after exposure to toxic Alexandrium dinoflagellates.

Heat shock proteins 70KD (Hsp70s) are highly conserved molecular chaperones with essential roles against biotic and abiotic stressors. Marine bivalves inhabit highly complex environments and could accumulate paralytic shellfish toxins (PSTs), the well-noted neurotoxins generated during harmful algal blooms. Here, we systematically analyzed Hsp70 genes (CfHsp70s) in Zhikong scallop (Chlamys farreri), an important aquaculture mollusk in China. Sixty-five CfHsp70s from eight sub-families were identified, and 47 of these genes showed expansion in the Hspa12 sub-family. After exposure to different PST-producing dinoflagellates, Alexandrium minutum and Alexandrium catenella, diverse CfHsp70s regulation presented in scallop hepatopancreas, mainly accumulating incoming PSTs, and kidneys, transforming PSTs into higher toxic analogs. All the up-regulated CfHsp70s were from CfHsp70B2, CfHspa12, and CfHspa5 sub-families. CfHsp70B2 sub-family was mainly induced in the hepatopancreas, and CfHspa12 sub-family was highly induced in the kidneys. CfHsp70s up-regulation under two dinoflagellates exposure was stronger in the kidneys (log2FC: 19.5 and 18.6) than that in hepatopancreas (log2FC: 4.3 and 6.1). Exposure to different Alexandrium species had varying effects, that in hepatopancreas, CfHsp70B2s were chronically induced only after A. catenella exposure, whereas in kidney, CfHspa12s were more acutely induced after exposure of A. minutum than A. caenella. Moreover, in Yesso scallops (Patinopecten yessoensis), only Hspa12s were up-regulated in hepatopancreas after A. catenella exposure, and all the Hsp70B2s were down-regulated. These organ-, toxin-, and species-dependent Hsp70 regulation suggested the functional diversity of duplicated Hsp70s in response to the stress by PST-producing algae. Our findings provide insights into the evolution and functional characteristics of Hsp70s in scallops.

Effects of stocking density on the growth performance, bacterial load and antioxidant response systems of noble scallop Chlamys nobilis.

Stocking density is a crucial factor in shellfish aquaculture that affects overall growth performance and health status. Present study analyzes the effects of stocking densities on growth, survival and hemolymph immune status of noble scallop Chlamys nobilis. The scallops with the same size were separately placed in the lantern cages (10 layers per cage) using high stocking density (500 scallops per cage) and low stocking density (100 scallops per cage) and cultivated in the same location for 60 days. The results indicated that the scallops cultivated at high stocking density had significantly higher mortality and slower growth than those cultivated at low stocking density. Moreover, the hemolymph of scallops cultivated at high density showed significantly higher bacterial load, higher reactive oxygen species (ROS), higher expression level of Nrf2 and lower expression level of Keap1, as well as lower antibacterial ability of Vibrio parahemolyticus than that of scallops cultivated at low density. The present results demonstrated that long-term overcrowding is detrimental for the scallops, which can not only lead to high mortality and slow growth, but also cause more vulnerable to pathogenic bacteria. Therefore, we speculated that high stocking density culture practice of scallops in China might be the root of infectious bacteria outbreaks.

The impact of ocean acidification on the gonads of three key Antarctic benthic macroinvertebrates.

CO2 atmospheric pressure is increasing since industrial revolution, leading to a lowering of the ocean surface water pH, a phenomenon known as ocean acidification, with several reported effects on individual species and cascading effects on marine ecosystems. Despite the great amount of literature on ocean acidification effects on calcifying organisms, the response of their reproductive system still remains poorly known. In the present study, we investigated the histopathological effects of low pH on the gonads of three key macroinvertebrates of the Terra Nova Bay (Ross Sea) littoral area: the sea urchin Sterechinus neumayeri, the sea star Odontaster validus and the scallop Adamussium colbecki. After 1 month of exposure at control (8.12) and reduced (7.8 and 7.6) pH levels, we dissected the gonads and performed histological analyses to detect potential differences among treatments. Results showed significant effects on reproductive conditions of A. colbecki and S. neumayeri, while O. validus did not show any kind of alteration. Present results reinforce the need to focus on ocean acidification effects on soft tissues, particularly the gonads, whose damage may exert large effects on the individual fitness, with cascading effects on the population dynamic of the species.

Dynamics of DNA Methylation and DNMT Expression During Gametogenesis and Early Development of Scallop Patinopecten yessoensis.

DNA methylation reprograms during gametogenesis and embryo development, which is essential for germ cell specification and genomic imprinting in mammals. Corresponding process remains poorly investigated in molluscs. Here, we examined global DNA methylation level in the gonads of scallop Patinopecten yessoensis during gametogenesis and in embryos/larvae at different stages. DNA methylation level fluctuates during gametogenesis and early development, peaking at proliferative stage of ovary, growing stage of testis, and in blastulae. To understand the mechanisms underlying these changes, we conducted genome-wide characterization of DNMT family and investigated their expression profiles based on transcriptomes and in situ hybridization. Three genes were identified, namely PyDNMT1, PyDNMT2, and PyDNMT3. Expression of PyDnmt3 agrees with DNA methylation level during oogenesis and early development, suggesting PyDNMT3 may participate in de novo DNA methylation that occurs mainly at proliferative stage of ovary and testis, and in blastulae and gastrulae. PyDnmt1 expression is positively correlated with DNA methylation level during spermatogenesis, and is higher at maturation stage of ovary and in 2-8 cell embryos than other stages, implying possible involvement of PyDNMT1 in DNA methylation maintenance during meiosis and embryonic development. This study will facilitate better understanding of the developmental epigenetic reprogramming in bivalve molluscs.

Proteome and Transcriptome Analysis of Ovary, Intersex Gonads, and Testis Reveals Potential Key Sex Reversal/Differentiation Genes and Mechanism in Scallop Chlamys nobilis.

Bivalve mollusks exhibit hermaphroditism and sex reversal/differentiation. Studies generally focus on transcriptional profiling and specific genes related to sex determination and differentiation. Few studies on sex reversal/differentiation have been reported. A combination analysis of gonad proteomics and transcriptomics was conducted on Chlamys nobilis to provide a systematic understanding of sex reversal/differentiation in bivalves. We obtained 4258 unique peptides and 93,731 unigenes with good correlation between messenger RNA and protein levels. Candidate genes in sex reversal/differentiation were found: 15 genes differentially expressed between sexes were identified and 12 had obvious sexual functions. Three novel genes (foxl2, ß-catenin, and sry) were expressed highly in intersex individuals and were likely involved in the control of gonadal sex in C. nobilis. High expression of foxl2 or ß-catenin may inhibit sry and activate 5-HT receptor and vitellogenin to maintain female development. High expression of sry may inhibit foxl2 and ß-catenin and activate dmrt2, fem-1, sfp2, sa6, Amy-1, APCP4, and PLK to maintain male function. High expression of sry, foxl2, and ß-catenin in C. nobilis may be involved in promoting and maintaining sex reversal/differentiation. The downstream regulator may not be dimorphic expressed genes, but genes expressed in intersex individuals, males and females. Different expression patterns of sex-related genes and gonadal histological characteristics suggested that C. nobilis may change its sex from male to female. These findings suggest highly conserved sex reversal/differentiation with diverged regulatory pathways during C. nobilis evolution. This study provides valuable genetic resources for understanding sex reversal/differentiation (intersex) mechanisms and pathways underlying bivalve reproductive regulation.

Expression characteristics and functional analysis of Krüppel-like factor 4 in adductor muscle and mantle of Zhikong scallop Chlamys farreri.

Krüppel-like factor 4 (KLF4) is an important transcription factor involving in formation and maintenance of muscles in mammals. However, no data are available on KLF4 function in shellfish muscles which play vital roles in the movement, stress response, and physiology in shellfish. In the present study, we revealed that the Klf4 mRNA of Zhikong scallop Chlamys farreri was expressed in most tissues, which has high level in adductor muscle, mantle, kidney, and testis. Positive signals of the Klf4 mRNA and protein were visible in all skeletal muscle fibers of adductor muscle, and all the cells of C. farreri mantle. Furthermore, the knockdown of Klf4 mRNA in adductor muscle and mantle by means of in vivo RNA interference led to some different phenotypes, including disordered arrangement of muscle fibers in adductor muscle and mantle, abnormal structures of skeletal muscles, and reduced muscle fibers under endepidermis of mantle. Our findings demonstrated that Klf4 plays important roles in maintenance of muscle functions in C. farreri adductor muscle and mantle, and suggested that its regulatory way in skeletal muscle may be different from the smooth muscle in shellfish.

Multiple field-based methods to assess the potential impacts of seismic surveys on scallops.

Marine seismic surveys are an important tool to map geology beneath the seafloor and manage petroleum resources, but they are also a source of underwater noise pollution. A mass mortality of scallops in the Bass Strait, Australia occurred a few months after a marine seismic survey in 2010, and fishing groups were concerned about the potential relationship between the two events. The current study used three field-based methods to investigate the potential impact of marine seismic surveys on scallops in the region: 1) dredging and 2) deployment of Autonomous Underwater Vehicles (AUVs) were undertaken to examine the potential response of two species of scallops (Pecten fumatus, Mimachlamys asperrima) before, two months after, and ten months after a 2015 marine seismic survey; and 3) MODIS satellite data revealed patterns of sea surface temperatures from 2006-2016. Results from the dredging and AUV components show no evidence of scallop mortality attributable to the seismic survey, although sub-lethal effects cannot be excluded. The remote sensing revealed a pronounced thermal spike in the eastern Bass Strait between February and May 2010, overlapping the scallop beds that suffered extensive mortality and coinciding almost exactly with dates of operation for the 2010 seismic survey. The acquisition of in situ data coupled with consideration of commercial seismic arrays meant that results were ecologically realistic, while the paired field-based components (dredging, AUV imagery) provided a failsafe against challenges associated with working wholly in the field. This study expands our knowledge of the potential environmental impacts of marine seismic survey and will inform future applications for marine seismic surveys, as well as the assessment of such applications by regulatory authorities.

Embryo-larvae and juvenile toxicity of Pb and Cd in Northern Chilean scallop Argopecten purpuratus.

This study aimed to investigate the effects of Cd and Pb on earlier stage of the commercially important scallop (Argopecten purpuratus) in the contamination context of Northern Chile where this specie is farmed, through acute exposure bioassays in embryo-larvae measuring cumulative abnormality (EC50) and juvenile cumulative mortality (LC50) as endpoints, based on environmentally detected concentrations and available toxicological data from similar species. Embryo-larvae exposure indicates 48 h EC50 of 1.55 mg/L Cd, and 0.044 mg/L Pb. On the contrary, 96 h LC50 in juvenile scallops was 0.48 mg/L Cd and 1.47 mg/L Pb. Our results demonstrated differential toxicity between embryo and juvenile scallops that might relate to different primary defense mechanisms or effect in morphological development of individuals in each ontogenetic stage. Compared to similar bivalve metal toxicity tests, this study demonstrated that A. purpuratus embryos are more sensitive to Pb than most other bivalve species. Our results indicate that maximum permitted levels of Pb in marine waters and estuaries (according to Chilean regulation) could pose a risk for scallops' first stage of life (embryo-larvae) development, and needs to be reviewed. Furthermore, Chilean environmental regulations do not have quality standards for marine sediments (currently under discussion), where high levels of metals have been continuously reported.

Complete characterization of new isolates of Neptunomonas phycophila leads to emend its description and opens possibilities of biotechnological applications.

Five strains were isolated from gonad of Great scallop (Pecten maximus) broodstock in a Norwegian hatchery. The study of 16S rRNA gene sequences showed that these isolates belong to Neptunomonas phycophila, a bacterium originally isolated from a symbiont of the anemone Aiptasia tagetes from Puerto Rico. The gyrB and rpoB genes sequences confirmed the affiliation of the scallop isolates to this species. Phenotypic characterization was performed and some differences between the Norwegian isolates and the type strain of N. phycophila were detected, such as ranges of temperature, pH, and tolerance to salinity or the use of several substrates as sole carbon source which lead to an emended description of the species. The strain 3CM2.5 showed phosphatidylethanolamine and phosphatidylglycerol as the major polar lipids. The whole genomes of the scallop strain 3CM2.5 and type strain of the species CECT 8716T were obtained and the annotation of these genomes revealed the presence of genes involved in degradation of aromatic compounds in both strains. Results obtained not only widen the geographical and host ranges of N. phycophila, but also point out possible biotechnological applications for this bacterial species.

Molecular characterization and expression analysis of the myostatin gene and its association with growth traits in Noble scallop (Chlamys nobilis).

Myostatin (MSTN), also called growth and differentiation factor-8 (GDF-8), is a member of the transforming growth factor-ß (TGF-ß) superfamily and an inhibitor of muscle differentiation and growth. In this report, we identified and characterized a MSTN gene (CnMSTN) from the scallop Chlamys nobilis. The open reading frame of CnMSTN was 1374bp in length, encoding 457 amino acids. The structure of CnMSTN included a putative signal peptide, a TGF-ß propeptide domain, and a conserved TGF-ß domain. Phylogenetic analysis showed that the CnMSTN gene was clustered in the same subgroup with the MSTN gene found in Mollusca. Quantitative real-time PCR showed that the CnMSTN gene was widely expressed in all tissues tested, with the highest expression level observed in the adductor muscle. Six single nucleotide polymorphisms (SNPs) were identified in the promoter region, but no SNP was detected in the exon regions. Association analysis showed that SNP g.-579A/C had significant effects on body mass, soft-tissue mass, and adductor muscle mass. The CC and AC genotypes of g.-579A/C had significantly higher growth trait values than that of genotype AA (P<0.05). These results suggest that CnMSTN could be used as a candidate gene for the selective breeding of C. nobilis.