Validation of housekeeping genes as internal controls for studying biomarkers of endocrine-disrupting chemicals in disk abalone by real-time PCR

Multi-omic approach to evaluate the response of gilt-head sea bream (Sparus aurata) exposed to the UV filter sulisobenzone

Sulisobenzone (BP-4) is one of the benzophenone type UV filters most frequently detected in aquatic ecosystems. As a suspected endocrine disrupting compound, scarce information is available yet about other molecular effects and its mechanism of action. Here, we used an integrated transcriptomic and metabolomic approach to improve the current understanding on the toxicity of BP-4 towards aquatic species. Gilt-head sea bream individuals were exposed at environmentally relevant concentrations (10 μg L^-1) for 22 days. Transcriptomic analysis revealed 371 differentially expressed genes in liver while metabolomic analysis identified 123 differentially modulated features in plasma and 118 in liver. Integration of transcriptomic and metabolomic data showed disruption of the energy metabolism (>10 pathways related to the metabolism of amino acids and carbohydrates were impacted) and lipid metabolism (5 glycerophospholipids and the expression of 3 enzymes were affected), suggesting oxidative stress. We also observed, for the first time in vivo and at environmental relevant concentrations, the disruption of several enzymes involved in the steroid and thyroid hormones biosynthesis. DNA and RNA synthesis was also impacted by changes in the purine and pyrimidine metabolisms. Overall, the multiomic workflow presented here increases the evidence on suspected effects of BP-4 exposure and identifies additional modes of action of the compounds that could have been overlooked by using single omic approaches.

Molecular Characterization of Carbonic Anhydrase II (CA II) and Its Potential Involvement in Regulating Shell Formation in the Pacific Abalone, Haliotis discus hannai

Carbonic anhydrases (CAs) are a family of metalloenzymes that can catalyze the reversible interconversion of CO₂/HCO₃^–, ubiquitously present in both prokaryotes and eukaryotes. In the present study, a CA II (designated as HdhCA II) was sequenced and characterized from the mantle tissue of the Pacific abalone. The complete sequence of HdhCA II was 1,169 bp, encoding a polypeptide of 349 amino acids with a NH₂-terminal signal peptide and a CA architectural domain. The predicted protein shared 98.57% and 68.59% sequence identities with CA II of Haliotis gigantea and Haliotis tuberculata, respectively. Two putative N-linked glycosylation motifs and two cysteine residues could potentially form intramolecular disulfide bond present in HdhCA II. The phylogenetic analysis indicated that HdhCA II was placed in a gastropod clade and robustly clustered with CA II of H. gigantea and H. tuberculata. The highest level of HdhCA II mRNA expression was detected in the shell forming mantle tissue. During ontogenesis, the mRNA of HdhCA II was detected in all stages, with larval shell formation stage showing the highest expression level. The in situ hybridization results detected the HdhCA II mRNA expression in the epithelial cells of the dorsal mantle pallial, an area known to express genes involved in the formation of a nacreous layer in the shell. This is the first report of HdhCA II in the Pacific abalone, and the results of this study indicate that this gene might play a role in the shell formation of abalone.

Carbonic Anhydrase in Pacific Abalone Haliotis discus hannai: Characterization, Expression, and Role in Biomineralization

Carbonic anhydrases (CAs) are universal zinc ion containing metalloenzymes that play a pivotal role in various physiological processes. In this study, a CA I (designated as Hdh CA I) was isolated and characterized from the mantle tissue of Pacific abalone, Haliotis discus hannai. The full-length cDNA sequence of Hdh CA I was 1,417-bp in length, encoding a protein of 337 amino acids with molecular weight of 37.58 kDa. Hdh CA I sequence possessed a putative signal peptide of 22 amino acids and a CA catalytic function domain. The predicted protein shared 94 and 78% sequence identities with Haliotis gigantea and Haliotis tuberculata CA I, respectively. Results of phylogenetic analysis indicated that Hdh CA I was evolutionarily close to CA I of H. gigantea and H. tuberculata with high bootstrap values. Significantly higher levels of Hdh CA I mRNA transcript were found in mantle than other examined tissues. In situ hybridization results showed strong hybridization signals in epithelial cells of the dorsal mantle pallial, an area known to synthesize and secrete proteins responsible for the nacreous layer formation of shell. This is the first study on Hdh CA I in H. discus hannai and the results may contribute to further study its physiological functions in shell biomineralization of abalone.

Effects of Antifreeze Protein III on Sperm Cryopreservation of Pacific Abalone, Haliotis discus hannai

Pacific abalone (Haliotis discus hannai) is a highly commercial seafood in Southeast Asia. The aim of the present study was to improve the sperm cryopreservation technique for this valuable species using an antifreeze protein III (AFPIII). Post-thaw sperm quality parameters including motility, acrosome integrity (AI), plasma membrane integrity (PMI), mitochondrial membrane potential (MMP), DNA integrity, fertility, hatchability, and mRNA abundance level of heat shock protein 90 (HSP90) were determined to ensure improvement of the cryopreservation technique. Post-thaw motility of sperm cryopreserved with AFPIII at 10 µg/mL combined with 8% dimethyl sulfoxide (DMSO) (61.3 ± 2.7%), 8% ethylene glycol (EG) (54.3 ± 3.3%), 6% propylene glycol (PG) (36.6 ± 2.6%), or 2% glycerol (GLY) (51.7 ± 3.0%) was significantly improved than that of sperm cryopreserved without AFPIII. Post-thaw motility of sperm cryopreserved with 2% MeOH and 1 µg/mL of AFPIII was also improved than that of sperm cryopreserved without AFPIII. A combination of 10 µg/mL AFPIII with 8% DMSO resulted in the highest post-thaw motility, showing AI of 60.1 ± 3.9%, PMI of 67.2 ± 4.0%, and MMP of 59.1 ± 4.3%. DNA integrity of sperm cryopreserved using 10 µg/mL AFPIII combined with 8% DMSO was not significantly (p > 0.05) different from that of fresh sperm. Cryopreservation using a combination of AFPIII with 8% DMSO improved fertilization and hatching rates of sperm compared to that of cryopreservation without supplementation of 10 µg/mL AFPIII. Sperm cryopreserved using AFPIII showed higher mRNA abundance levels of HSP90 than those cryopreserved without AFPIII. Results of the present study suggest that 10 µg/mL AFPIII combined with 8% DMSO can be used for large scale cryopreservation of Pacific abalone sperm and for hatchery production.

Selection and Validation of the Optimal Panel of Reference Genes for RT-qPCR Analysis in the Developing Rat Cartilage

Real-time fluorescence quantitative PCR (RT-qPCR) is widely used to detect gene expression levels, and selection of reference genes is crucial to the accuracy of RT-qPCR results. Minimum Information for Publication of RT-qPCR Experiments (MIQE) proposes that using the panel of reference genes for RT-qPCR is conducive to obtaining accurate experimental results. However, the selection of the panel of reference genes for RT-qPCR in rat developing cartilage has not been well documented. In this study, we selected eight reference genes commonly used in rat cartilage from literature (GAPDH, ACTB, 18S, GUSB, HPRT1, RPL4, RPL5, and SDHA) as candidates. Then, we screened out the optimal panel of reference genes in female and male rat cartilage of fetus (GD20), juvenile (PW6), and puberty (PW12) in physiology with stability analysis software of genes expression. Finally, we verified the reliability of the selected panel of reference genes with the rat model of intrauterine growth retardation (IUGR) induced by prenatal dexamethasone exposure (PDE). The results showed that the optimal panel of reference genes in cartilage at GD20, PW6, and PW12 in physiology was RPL4 + RPL5, which was consistent with the IUGR model, and there was no significant gender difference. Further, the results of standardizing the target genes showed that RPL4 + RPL5 performed smaller intragroup differences than other panels of reference genes or single reference genes. In conclusion, we found that the optimal panel of reference genes in female and male rat developing cartilage was RPL4 + RPL5, and there was no noticeable difference before and after birth.

Quadruple domain-containing galectin from marine invertebrate disk abalone (Haliotis discus discus): Molecular perspectives in early development, immune expression, and potent antiviral responses

Galectins are well-known β-galactoside-binding proteins, which play vital roles in innate immune responses of both vertebrates and invertebrates. However, knowledge regarding invertebrate galectins is still in its infancy. With the intention of filling the knowledge gap, here we identified a quadruple domain-containing galectin from marine invertebrate disk abalone, Haliotis discus discus (AbGalec), and characterized it. AbGalec consisted of four distinct carbohydrate-recognition domains (CRDs) and lacked a signal peptide. Expression analysis revealed AbGalec to be ubiquitously expressed in all the examined early embryonic stages of abalone, with highest expression in the 16-cell stage, suggesting the importance of AbGalec in early developmental processes. Tissue distribution analysis revealed the highest expression of AbGalec in abalone mantle, followed by that in gills and hemocytes. Immune challenge experiments revealed significant upregulation of AbGalec at 24 h and 48 h post injection (p.i.) with bacterial and viral components. These results suggested the possible involvement of AbGalec in host defense mechanisms. Polyinosinic: polycytidylic acid (Poly I:C) and viral hemorrhagic septicemia virus (VHSV) injections were capable of inducing AbGalec transcript expression more prominently than bacterial stimulants, thus providing evidence for its role in viral infections. We determined the virus-neutralizing ability of a quadruple domain-containing galectin for the first time, by analyzing the downregulation of VHSV transcripts during the overexpression of AbGalec. Significant downregulation of VHSV transcripts was observed after 24 h and 48 h of post infection. Collectively, our findings reveal the potent antiviral responses of molluscan quadruple domain-containing galectin, AbGalec, along with its involvement in innate immunity.

Characterization of Insulin-Like Growth Factor Binding Protein 7 (Igfbp7) and Its Potential Involvement in Shell Formation and Metamorphosis of Pacific Abalone, Haliotis discus hannai

Insulin-like growth factor binding proteins (IGFBPs) are secreted proteins that play an important role in IGF regulation of growth and development of vertebrate and invertebrates. In this study, the IGFBP7 gene was cloned and characterized from mantle tissues of H. discus hannai, and designated as Hdh IGFBP7. The full-length cDNA sequence transcribed from the Hdh IGFBP7 gene was 1519-bp long with an open reading frame of 720-bp corresponding to a putative polypeptide of 239 amino acids. The molecular mass of its mature protein was approximately 23.44 KDa with an estimated isoelectric point (pI) of 5.35, and it shared significant homology with IGFBP7 gene of H. madaka. Hdh IGFBP7 has a characteristic IGFBP N-terminal domain (22–89 aa), a kazal-type serine proteinase inhibitor domain (77–128), and an immunoglobulin-like C2 domain (144–223). Furthermore, twelve cysteine residues and a signature motif of IGFBPs (XCGCCXXC) were found in its N-terminal domain. Phylogenetic analysis revealed that Hdh IGFBP7 was aligned with IGFBP7 of H. madaka. Tissue distribution analysis showed that the mRNA of Hdh IGFBP7 was expressed in all examined tissues, with the highest expression level observed in the mantle and gill tissues. The expression level of Hdh IGFBP7 mRNA was relatively higher at the juvenile stage during its metamorphosis period. In situ hybridization showed that Hdh IGFBP7 transcript was expressed in epithelial cells of the dorsal mantle pallial and mucus cells of the branchial epithelium in gill. These results provide basic information for future studies on the role of IGFBP7 in IGF regulation of shell growth, development and metamorphosis of abalone.

Reference genes for proximal femoral epiphysiolysis expression studies in broilers cartilage

The use of reference genes is required for relative quantification in gene expression analysis and the stability of these genes can be variable depending on the experimental design. Therefore, it is indispensable to test the reliability of endogenous genes previously to their use. This study evaluated nine candidate reference genes to select the most stable genes to be used as reference in gene expression studies with the femoral cartilage of normal and epiphysiolysis-affected broilers. The femur articular cartilage of 29 male broilers with 35 days of age was collected, frozen and further submitted to RNA extraction and quantitative PCR (qPCR) analysis. The candidate reference genes evaluated were GAPDH, HMBS, HPRT1, MRPS27, MRPS30, RPL30, RPL4, RPL5, and RPLP1. For the gene stability evaluation, three software were used: GeNorm, BestKeeper and NormFinder, and a global ranking was generated using the function RankAggreg. In this study, the RPLP1 and RPL5 were the most reliable endogenous genes being recommended for expression studies with femur cartilage in broilers with epiphysiolysis and possible other femur anomalies.

Ovarian transcriptome profiles associated with sexual maturation in Pacific abalone (Haliotis discus hannai)

BACKGROUND

There is now abundant information on genes involved in molluscan oogenesis and their associations with ovarian development. However, few studies have investigated the ovarian transcriptome of Pacific abalone (Haliotis discus hannai).

OBJECTIVE

The objective of this study was to identify genes related to ovarian development and maturation in Pacific abalone utilizing RNA-sequencing (RNA-seq) and to verify the genes most relevant to different stages of maturation.

METHODS

RNA samples from the ovarian tissues of sexually immature and mature abalone were used to construct cDNA libraries, which were paired-end sequenced on an Illumina HiSeq 2500 platform. Reads from individual samples (unigenes) were aligned to reference transcriptome databases for identification of differentially expressed genes (DEGs) between immature and mature ovarian libraries. Reverse transcription-quantitative polymerase chain reaction was used to verify the RNA-seq data.

RESULTS

A total of 8779 unigenes were obtained from the ovaries of immature and mature abalone, with a total length of 3323,279 bp and an average length of 379 bp per gene. Gene ontology analysis assigned 5860 unigenes to biological processes, 855 to cellular components, and 1352 to molecular functions. Overall, 470 DEGs were identified, including 213 and 257 genes down-regulated and up-regulated in mature abalone, respectively. Among these, 13 relevant transcripts, including VTG1 and FZD7, were significantly highly expressed in the ovaries of mature abalone (p < 0.05, fold change > 2).

CONCLUSION

This H. discus hannai ovary transcriptome provides molecular targets to better understand ovarian development, oogenesis, and sexual maturation, and to enhance Pacific abalone production.

Characterization of Insulin-Like Growth Factor Binding Protein-5 (IGFBP-5) Gene and Its Potential Roles in Ontogenesis in the Pacific Abalone, Haliotis discus hannai

Insulin-like growth factor binding protein family is known to be involved in regulating biological actions of insulin-like growth factors (IGFs). In the present study, a full-length cDNA encoding the IGFBP-5 gene was cloned and characterized from the cerebral ganglion of Haliotis discus hannai. The 921-bp full-length sequence of Hdh IGFBP-5 cDNA transcript had an open reading frame of 411 bp encoding a predicted polypeptide of 136 amino acids, sharing high sequence identities with IGFBP-5 of H. diversicolor. The deduced Hdh IGFBP-5 protein contained a putative transmembrane domain (13-35 aa) in the N-terminal region. It also possessed a signature domain of IGFBP protein family (IB domain, 45-120 aa). Six cysteine residues (Cys-47, Cys-55, Cys-73, Cys-85, Cys-98, and Cys-118) in this cloned sequence could potentially form an intrachain disulfide bond. Phylogenetic analysis indicated that the Hdh IGFBP-5 gene was robustly clustered with IGFBP-5 of H. diversicolor. Tissue distribution analysis based on qPCR assay showed that Hdh IGFBP-5 was widely expressed in all examined tissues, with significantly (p < 0.05) higher expression in the cerebral ganglion. In male and female gametogenetic cycles, Hdh IGFBP-5 mRNA was expressed at all stages, showing significantly higher level at ripening stage. The expression level of Hdh IGFBP-5 mRNA was significantly higher in the polar body stage than in other ontogenic stages. In situ hybridization revealed that Hdh IGFBP-5 mRNA was present in the neurosecretory cells of the cerebral ganglion. This is the first study describing IGFBP-5 in H. discus hannai that might be synthesized in the neural ganglia. Our results demonstrate Hdh IGFBP-5 is involved in regulating ontogenic development and reproductive regulation of H. discus hannai.

Structural and functional analysis of three Iκb kinases (IKK) in disk abalone (Haliotis discus discus): Investigating their role in the innate immune responses

The IκB kinases (IKK) are large multiprotein complexes that regulate the activation of the transcription factor NF-κB and are involved in a diverse range of biological processes, including innate immunity, inflammation, and development. To explore the potential roles of invertebrate IKKs on immunity, three IKK encoding genes have been identified from molluscan species disk abalone and designed as AbIKK1, AbIKK2 and AbIKK3 at the transcriptional level. Coding sequences of AbIKK1, AbIKK2 and AbIKK3 encode the peptides of 746, 751 and 713 amino acids with the predicted molecular mass of 86.16, 86.12 and 81.88 kDa respectively. All three AbIKKs were found to share conserved IKK family features including the kinase superfamily domain (KD), ubiquitin-like domain (ULD), and α-helical scaffold/dimerization domain (SDD), similar to their mammalian counterparts. Under normal physiological conditions, AbIKKs were ubiquitously detected in six different tissues, with the highest abundance in the digestive tract and gills. Temporal transcriptional profiles in abalone hemocytes revealed the induction of AbIKK1, AbIKK2, and AbIKK3 expression following exposure to Gram-negative (Vibrio parahemolyticus) and Gram-positive (Listeria monocytogenes) bacteria, viruses (viral hemorrhagic septicemia virus, VHSV), LPS, or poly I:C. The overexpression of AbIKKs in HEK293T or RAW264.7 murine macrophage cells induced NF-κB promoter activation independent of stimulation by TNF-α or LPS. Moreover, iNOS and COX2 expression was induced in AbIKK transfected RAW264.7 murine macrophage cells and the induced state was maintained post-LPS treatment. Furthermore, mRNA levels of three selected cytokine-encoding genes (IL-1β, IL-6, and TNF-α) were found to be elevated in abalone IKK overexpressed RAW264.7 murine macrophage cells, both with and without LPS exposure. Overall, our findings demonstrated that AbIKKs identified in this study were positively involved in eliciting innate immune responses in abalone. In addition, the data revealed the presence of an evolutionarily conserved signaling mechanism for IKK mediated NF-κB activation in mollusks.

Molecular Identification, Characterization, and Expression Analysis of a Gonadotropin-Releasing Hormone Receptor (GnRH-R) in Pacific Abalone, Haliotis discus hannai

A full-length cDNA sequence encoding a GnRH receptor was cloned from the pleuropedal ganglion of the Pacific abalone, Haliotis discus hannai. The cloned sequence is 1499-bp in length encoding a protein of 460 amino acid residues, with a molecular mass of 52.22 kDa and an isoelectric point (pI) of 9.57. The architecture of HdhGnRH-R gene exhibited key features of G protein-coupled receptors (GPCRs), including seven membrane spanning domains, putative N-linked glycosylation motifs, and phosphorylation sites of serine and threonine residues. It shared 63%, 52%, and 30% sequence identities with Octopus vulgaris, Limulus polyphemus, and Mizuhopecten yessoensis GnRH-R II sequences, respectively. Phylogenetic analysis indicated that HdhGnRH-R gene was clustered with GnRH-R II of O. vulgaris and O. bimaculoides. qPCR assay demonstrated that the mRNA expression level of this receptor was significantly higher in the pleuropedal ganglion than that in any other examined tissue. Transcriptional activities of this gene in gonadal tissues were significantly higher in the ripening stage. The mRNA expression of this gene was significantly higher in pleuropedal ganglion, testis, and ovary at higher effective accumulative temperature (1000 °C). In situ hybridization revealed that HdhGnRH-R mRNA was expressed in neurosecretory cells of pleuropedal ganglion. Our results suggest that HdhGnRH-R gene synthesized in the neural ganglia might be involved in the control of gonadal maturation and gametogenesis of H. discus hannai. This is the first report of GnRH-R in H. discus hannai and the results may contribute to further studies of GPCRs evolution or may useful for the development of aquaculture method of this abalone species.

Tissue-specific evaluation of suitable reference genes for RT-qPCR in the pond snail, Lymnaea stagnalis

Reverse transcription quantitative PCR (RT-qPCR) is a robust technique for the quantification and comparison of gene expression. To obtain reliable results with this method, one or more reference genes must be employed to normalize expression measurements among treatments or tissue samples. Candidate reference genes must be validated to ensure that they are stable prior to use in qPCR experiments. The pond snail (Lymnaea stagnalis) is a common research organism, particularly in the areas of learning and memory, and is an emerging model for the study of biological asymmetry, biomineralization, and evolution and development. However, no systematic assessment of qPCR reference genes has been performed in this animal. Therefore, the aim of our research was to identify stable reference genes to normalize gene expression data from several commonly studied tissues in L. stagnalis as well as across the entire body. We evaluated a panel of seven reference genes across six different tissues in L. stagnalis with RT-qPCR. The genes included: elongation factor 1-alpha, glyceraldehyde-3-phosphate dehydrogenase, beta-actin, beta-tubulin, ubiquitin, prenylated rab acceptor protein 1, and a voltage gated potassium channel. These genes exhibited a wide range of expression levels among tissues. The tissue-specific stability of each of the genes was consistent when measured by the standard stability assessment algorithms: geNorm, NormFinder, BestKeeper, and RefFinder. Our data indicate that the most stable reference genes vary among the tissues that we examined (central nervous system, tentacles, lips, penis, foot, mantle). Our results were generally congruent with those obtained from similar studies in other molluscs. Given that a minimum of two reference genes are recommended for data normalization, we provide suggestions for strong pairs of reference genes for single- and multi-tissue analyses of RT-qPCR data in L. stagnalis.

Immune and xenobiotic responses of glutathione S-Transferase theta (GST-θ) from marine invertebrate disk abalone (Haliotis discus discus): With molecular characterization and functional analysis

Representing a multifunctional complex group of proteins, glutathione S- transferases (GSTs) play a major role in the phase II detoxification process in a wide range of organisms. This study focused on the potential detoxification ability of disk abalone (Haliotis discus discus) GST theta (AbGST-θ) under different stress conditions with special reference to post immune challenges. Characterization of AbGST-θ revealed with 226 amino acids, 26.6 kDa of predicted molecular mass and 8.9 of theoretical isoelectric point. As illustrated in the multiple sequence alignment, eight glutathione binding sites (G-sites) and ten substrate binding sites (H-sites) were identified in well-distinct N-terminal and C-terminal domains of AbGST-θ, respectively. AbGST-θ exhibited its highest sequence identity with Mizuhopecten yessoensis (59.1%) and the phylogenetic tree clearly positioned AbGST-θ with pre-defined GST-θ molluscan homologues. The AbGST-θ was highly expressed in the digestive tract of un-challenged abalones. Upon administering the challenge experiment, AbGST-θ showed significant modulations in their transcriptional levels depending on the time and the tissue type. The optimum temperature was 37 °C and optimum pH was 7.5 for AbGST-θ. The determined enzyme kinetic parameters of AbGST-θ showed low affinity towards 1-Chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH) as substrates. Nonetheless, with Cibacron blue IC₅₀ (half maximal inhibitory concentration) was calculated to be 0.08 μM while observing 100% inhibition with 100 μM. Furthermore, AbGST-θ resulted in significant protection ability towards H₂O₂, CdCl_2, and ZnCl₂ in the disk diffusion assay. Collectively, this study provides evidences for the detoxification ability and the immunological host defensive capability of AbGST-θ in disk abalone.

Molecular characterization, expression analysis, and functional properties of multiple 5-hydroxytryptamine receptors in Pacific abalone (Haliotis discus hannai)

Neurotransmitters such as serotonin (5-hydroxytryptamine; 5-HT) in the central nervous system regulate diverse physiological functions, including reproduction, feeding, learning, and memory, in diverse animal phyla. 5-HT and the 5-HT1 subtype receptor play important roles in sexual maturation and in the initiation of gamete release in mollusks. However, little is known about the involvement of other 5-HT receptor subfamilies in the reproduction process. In the present study, we identified the cDNAs encoding eight subtypes of 5-HT receptors from the ganglia tissues of the Pacific abalone Haliotis discus hannai (Mollusca; Gastropoda; Haliotidae), and examined the gonadal expression of the transcripts of 5-HT receptors. A phylogenetic analysis indicated that the molluskan 5-HT receptors are largely classified into four major clades: 5-HT1/5/7, 5-HT2, 5-HT4, and 5-HT6. Among the H. discus hannai (Hdh) 5-HT1-7 transcripts, Hdh5-HT1B, 4A, 4B, and 6 were the major subtypes detected in the mature ovary. Estradiol-17β injection into the pedal sinus induced the downregulation of 5-HT4B and upregulation of 5-HT6 transcripts in the ovary of mature abalone within 72 h. In HEK293 cells overexpressing Hdh5-HT1B, forskolin-stimulated cAMP response element luciferase (CRE-Luc) reporter activity was inhibited by 5-HT in a dose-dependent manner, whereas serum response element luciferase (SRE-Luc) activity was not affected. In Hdh5-HT4A-expressing HEK293 cells, forskolin-stimulated CRE-Luc and SRE-Luc reporter activities were both marginally increased by treatment with a high dose of 5-HT. Our results provide new insights into the roles of 5-HT through diverse G protein-coupled 5-HT receptors in the reproductive process of mollusks.

Transcriptome-wide identification, functional characterization, and expression analysis of two novel invertebrate-type Toll-like receptors from disk abalone (Haliotis discus discus)

Toll-like receptors (TLRs) are well-known pattern recognition receptors that play key immunological roles in a diverse range of organisms. In this study, two novel invertebrate TLRs from disk abalone (designated as AbTLR-A and AbTLR-B) were identified and functionally characterized for the first time. AbTLR-A and AbTLR-B comprised the typical TLR domain architecture containing an extracellular leucine-rich repeat domain, transmembrane domain, and Toll/interleukin-1 receptor domain. Expressional analysis revealed that both TLRs were constitutively expressed at all the early embryonic stages of disk abalone analyzed, with the highest level of AbTLR-A found at the 16-cell stage and AbTLR-B at the trochophore stage. According to tissue distribution analysis, prominent mRNA expression of AbTLR-A and AbTLR-B was detected in the hemocytes and gills, respectively. AbTLR-A and AbTLR-B mRNAs were significantly up-regulated in response to Gram-negative Vibrio parahemolyticus, Gram-positive Listeria monocytogenes, and viral hemorrhagic septicemia virus injections in abalone hemocytes and gills. Overexpression of AbTLR-A and AbTLR-B in HEK293T cells directly activated nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) responsive reporters. Neither TLRs showed a high response to pathogen-associated molecular patterns in vitro. Co-expression of AbTLR-A and AbTLR-B with AbMyD88-2 and AbMyD88-X activated NF-κB-responsive reporters in a synergetic manner. These findings demonstrate the involvement of AbTLR-A and AbTLR-B in abalone innate immunity.

Selection of reference genes for reverse transcription-qPCR analysis in the biomonitor macrophyte Bidens laevis L

The RT-qPCR has been the method used to analyze gene expression in plants but its benefits have not been completely exploited in the field of plants ecotoxicology when used as molecular biomarkers. The correct use of RT-qPCR demands to establish a certain number of reference genes (RG) which are expected to be invariable in their expression although it does not always happen. The main goals of this work were to: (1) analyze the stability of six potential RG, (2) establish the optimum number of RG, (3) select the most suitable RG to be applied in Bidens laevis under different test conditions and tissues and (4) confirm its convenience by normalizing the expression of one gene of interest under three different challenges. When all data were pooled together, the geNorm algorithm pointed out beta-actin and beta-tubulin (TUB) as the optimal RG pair while NormFinder algorithm selected nicotinamide adenine dinucleotide dehydrogenase (NADHD) and histone 3 (H3) as possessing the most invariable levels of expression. On the other hand, when data were grouped by tissues, ANOVA test selected H3 and TUB, while data grouped by conditions indicated that H3 and NADHD were the most stable RG under this analysis. Therefore, for a general-purpose set of RG, the overall analysis showed that a set of three RG would be optimum, and H3, TUB and NADHD were the selected ones. On the other hand, as RG can vary depending on the tissues or conditions, results achieved with ANOVA would be more reliable. Thus, appropriate normalization process would clearly need more than one RG.

Identification and validation of reference genes for qPCR in the terrestrial gastropod Cepaea nemoralis

Identifying and understanding mechanisms that generate phenotypic diversity is a fundamental goal of evolutionary biology. With a diversity of pigmented shell morphotypes governed by Mendelian patterns of inheritance, the common grove snail Cepaea nemoralis (Linnaeus, 1758) has been a model for evolutionary biologists and population geneticists for decades. However, the genetic mechanisms by which C. nemoralis generates this pigmented shell diversity remain unknown. An important first step in investigating this pigmentation pattern is to establish a set of validated reference genes for differential gene expression assays. Here we have evaluated eleven candidate genes for reverse transcription quantitative polymerase chain reaction (qPCR) in C. nemoralis. Five of these were housekeeping genes traditionally employed as qPCR reference genes in other species, while six alternative genes were selected de novo from C. nemoralis transcriptome data based on the stability of their expression levels. We tested all eleven candidates for expression stability in four sub-adult tissues of C. nemoralis: pigmented mantle, unpigmented mantle, head and foot. We find that two commonly employed housekeeping genes (alpha tubulin, glyceraldehyde 3-phosphate dehydrogenase) are unsuitable for use as qPCR reference genes in C. nemoralis. The traditional housekeeping gene UBIquitin on the other hand performed very well. Additionally, an RNA-directed DNA polymerase (RNAP), a Potassium Channel Protein (KCHP) and a Prenylated Rab acceptor protein 1 (PRAP), identified de novo from transcriptomic data, were the most stably expressed genes in different tissue combinations. We also tested expression stability over two seasons and found that, although other genes are more stable within a single season, beta actin (BACT) and elongation factor 1 alpha (EF1α) were the most reliable reference genes across seasons.

Molecular identification and functional analysis of two variants of myeloid differentiation factor 88 (MyD88) from disk abalone (Haliotis discus discus)

Myeloid differentiation factor 88 (MyD88) is a crucial adaptor protein of the Toll-like receptor (TLR)- and interleukin 1 receptor-mediated signaling pathways and is involved in a diverse array of inflammatory responses via NF-κB activation. In the present study, two MyD88 variants were identified from disk abalone (Haliotis discus discus) and designated AbMyD88-2 and AbMyD88-X. The deduced AbMyD88-2 and AbMyD88-X comprised 433 and 354 amino acids with predicted molecular masses of 48.85 kDa and 40.17 kDa, respectively. AbMyD88-2 and AbMyD88-X possessed typical MyD88 domain structural features including an N-terminal death domain (DD) and C-terminal toll interleukin 1 receptor (TIR) domain similar to those in mammals. Expression analysis of AbMyD88-2 and AbMyD88-X mRNA at different early embryonic developmental stages of abalone by qPCR revealed that their constitutive expression at all developmental stages analyzed with the considerably higher values at the 16-cell (AbMyD88-2) and morula stages (AbMyD88-X). In unchallenged disk abalones, AbMyD88-2 was highly expressed in muscles, while AbMyD88-X mRNA was predominantly transcribed in hemocytes. Moreover, AbMyD88-2 and AbMyD88-X mRNA were differentially modulated in abalone hemocytes after a challenge with live bacteria (Vibrio parahaemolyticus, Listeria monocytogenes), virus (viral hemorrhagic septicemia virus), and pathogen-associated molecular patterns (lipopolysaccharides and Poly I:C). Overexpression of AbMyD88-2 and AbMyD88-X in HEK293T cells induced the activation of the NF-κB promoter. AbMyD88-2 and AbMyD88-X involvement in inflammatory responses was characterized by their overexpression in RAW264.7 murine macrophage cells. These results revealed comparatively higher NO (Nitric oxide) production, induction of inflammatory mediator genes (iNOS and COX2), and proinflammatory genes (IL1β, IL6 and TNFα) expression in abalone MyD88s-overexpressing cells than in mock control in the presence or absence of LPS stimulation. Altogether, these results suggest that existence of a MyD88-dependent like signaling pathway in disk abalone and that both AbMyD88-2 and AbMyD88-X might be involved in innate immune and inflammatory responses.

Identification and characterization of molluscan caveolin-1 ortholog from Haliotis discus discus: Possible involvement in embryogenesis and host defense mechanism against pathogenic stress

Caveolins are principal membrane proteins of caveolae that play a central role in signal transduction, substrate transport, and membrane trafficking in various cell types. Numerous studies have reported the crucial role of caveolin-1 (CAV1) in response to invading microbes; yet, very little is known about molluscan CAV1. In this study, we identified and characterized CAV1 ortholog from the disk abalone, Haliotis discus discus (HdCAV1). The cDNA sequence of HdCAV1 is 826 bp long and encodes a 127-amino acid polypeptide. Characteristic caveolin superfamily domain (Glu³ - Lys¹²⁶) and two possible transmembrane domains (Cys⁴⁸ - Tyr⁶⁷ and Ile¹⁰³ - Phe¹²⁰) were identified in the HdCAV1 protein. Homology analysis revealed that HdCAV1 shared higher identity (>47%) with molluscans, but lower identity with other species. Phylogenetic tree constructed by the neighbor-joining (NJ) method revealed a distinct evolutionary pathway for molluscans. Transcriptional analysis by SYBR Green qPCR showed the highest expression of HdCAV1 mRNA in late veliger stage, as compared to that in other embryonic developmental stages of disk abalone. In adult animals, gill tissue showed highest HdCAV1 transcript levels under normal physiological condition. Stimulations with two bacteria (Vibrio parahaemolyticus and Listeria monocytogenes), viral hemorrhagic septicemia virus, and two pathogen-associated molecular patterns (LPS and poly I:C) significantly modulated the expression of HdCAV1 transcripts. Collectively, these data suggest that CAV1 plays an important role in embryogenesis and host immune defense in disk abalone.

Molecular identification of disk abalone (Haliotis discus discus) tetraspanin 33 and CD63: Insights into potent players in the disk abalone host defense system

Tetraspanins are a superfamily of transmembrane proteins involved in a diverse range of physiological processes including differentiation, adhesion, signal transduction, cell motility, and immune responses. In the present study, two tetraspanins, CD63 and tetraspanin 33 (TSPAN33) from disk abalone (AbCD63 and AbTSPAN33), were identified and characterized at the molecular level. The coding sequences for AbCD63 and AbTSPAN33 encoded polypeptides of 234 and 290 amino acids (aa) with predicted molecular mass of 25.3 and 32.5 kDa, respectively. The deduced AbCD63 and AbTSPAN33 protein sequences were also predicted to have a typical tetraspanin domain architecture, including four transmembrane domains (TM), short N- and C- terminal regions, a short intracellular loop, as well as a large and small extracellular loop. A characteristic CCG motif and cysteine residues, which are highly conserved across CD63 and TSPAN33 proteins of different species, were present in the large extracellular loop of both abalone tetraspanins. Phylogenetic analysis revealed that the AbCD63 and AbTSPAN33 clustered in the invertebrate subclade of tetraspanins, thus exhibiting a close relationship with tetraspanins of other mollusks. The AbCD63 and AbTSPAN33 mRNA transcripts were detected at early embryonic development stages of disk abalone with significantly higher amounts at the trochophore stage, suggesting the involvement of these proteins in embryonic development. Both AbCD63 and AbTSPAN33 were ubiquitously expressed in all the tissues of unchallenged abalones analyzed, with the highest expression levels found in hemocytes. Moreover, significant induction of AbCD63 and AbTSPAN33 mRNA expression was observed in immunologically important tissues, such as hemocytes and gills, upon stimulation with live bacteria (Vibrio parahaemolyticus and Listeria monocytogenes), virus (viral hemorrhagic septicemia virus), and two potent immune stimulators [polyinosinic:polycytidylic acid (poly I:C) and lipopolysaccharide (LPS)]. Collectively, these findings suggest that AbCD63 and AbTSPAN33 are involved in innate immune responses in disk abalone during pathogenic stress.

Selection of housekeeping genes as internal controls for quantitative RT-PCR analysis of the veined rapa whelk (Rapana venosa)

Background

The veined rapa whelk Rapana venosa is an important commercial shellfish in China and quantitative real-time PCR (qRT-PCR) has become the standard method to study gene expression in R. venosa. For accurate and reliable gene expression results, qRT-PCR assays require housekeeping genes as internal controls, which display highly uniform expression in different tissues or stages of development. However, to date no studies have validated housekeeping genes in R. venosa for use as internal controls for qRT-PCR.

Methods

In this study, we selected the following 13 candidate genes for suitability as internal controls: elongation factor-1α (EF-1α), α-actin (ACT), cytochrome c oxidase subunit 1 (COX1), nicotinamide adenine dinucleotide dehydrogenase (ubiquinone) 1α subcomplex subunit 7 (NDUFA7), 60S ribosomal protein L5 (RL5), 60S ribosomal protein L28 (RL28), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), β-tubulin (TUBB), 40S ribosomal protein S25 (RS25), 40S ribosomal protein S8 (RS8), ubiquitin-conjugating enzyme E2 (UBE2), histone H3 (HH3), and peptidyl-prolyl cis-trans isomerase A (PPIA). We measured the expression levels of these 13 candidate internal controls in eight different tissues and twelve larvae developmental stages by qRT-PCR. Further analysis of the expression stability of the tested genes was performed using GeNorm and RefFinder algorithms.

Results

Of the 13 candidate genes tested, we found that EF-1α was the most stable internal control gene in almost all adult tissue samples investigated with RL5 and RL28 as secondary choices. For the normalization of a single specific tissue, we suggested that EF-1α and NDUFA7 are the best combination in gonad, as well as COX1 and RL28 for intestine, EF-1α and RL5 for kidney, EF-1α and COX1 for gill, EF-1α and RL28 for Leiblein and mantle, EF-1α, RL5, and NDUFA7 for liver, GAPDH, PPIA, and RL28 for hemocyte. From a developmental perspective, we found that RL28 was the most stable gene in all developmental stages measured, and COX1 and RL5 were appropriate secondary choices. For the specific developmental stage, we recommended the following combination for normalization, PPIA, RS25, and RL28 for stage 1, RL5 and RL28 for stage 2 and 5, RL28 and NDUFA7 for stage 3, and PPIA and TUBB for stage 4.

Discussion

Our results are instrumental for the selection of appropriately validated housekeeping genes for use as internal controls for gene expression studies in adult tissues or larval development of R. venosa in the future.

Characterization and spatiotemporal expression of gonadotropin-releasing hormone in the Pacific abalone, Haliotis discus hannai

Gonadotropin-releasing hormone (GnRH) is a key neuropeptide regulating reproduction in humans and other vertebrates. Recently, GnRH-like cDNAs and peptides were reported in marine mollusks, implying that GnRH-mediated reproduction is an ancient neuroendocrine system that arose prior to the divergence of protostomes and deuterostomes. Here, we evaluated the reproductive control system mediated by GnRH in the Pacific abalone Haliotis discus hannai. We cloned a prepro-GnRH cDNA (Hdh-GnRH) from the pleural-pedal ganglion (PPG) in H. discus hannai, and analyzed its spatiotemporal gene expression pattern. The open reading frame of Hdh-GnRH encodes a protein of 101 amino acids, consisting of a signal peptide, a GnRH dodecapeptide, a cleavage site, and a GnRH-associated peptide. This structure and sequence are highly similar to GnRH-like peptides reported for mollusks and other invertebrates. Quantitative polymerase chain reaction demonstrated that Hdh-GnRH mRNA was more strongly expressed in the ganglions (PPG and cerebral ganglion [CG]) than in other tissues (gonads, gills, intestine, hemocytes, muscle, and mantle) in both sexes. In females, the expression levels of Hdh-GnRH mRNA in the PPG and branchial ganglion (BG) were significantly higher at the ripe and partial spent stages than at the early and late active stages. In males, Hdh-GnRH mRNA levels in the BG showed a significant increase in the partial spent stage. Unexpectedly, Hdh-GnRH levels in the CG were not significantly different among the examined stages in both sexes. These results suggest that Hdh-GnRH mRNA expression profiles in the BG and possibly the PPG are tightly correlated with abalone reproductive activities.

An invertebrate signal transducer and activator of transcription 5 (STAT5) ortholog from the disk abalone, Haliotis discus discus: Genomic structure, early developmental expression, and immune responses to bacterial and viral stresses

Signal transducer and activator of transcription (STAT) family members are key signaling molecules that transduce cellular responses from the cell membrane to the nucleus upon Janus kinase (JAK) activation. Although seven STAT members have been reported in mammals, very limited information on STAT genes in molluscans is available. In this study, we identified and characterized a STAT paralog that is homologous to STAT5 from the disk abalone, Haliotis discus discus, and designated as AbSTAT5. Comparison of the deduced amino acid sequence for AbSTAT5 (790 amino acids) with other counterparts revealed conserved residues important for functions and typical domain regions, including the N-terminal domain, coiled-coil domain, DNA-binding domain, linker domain, and Src homology 2 (SH2) domains as mammalian counterparts. Analysis of STAT phylogeny revealed that AbSTAT5 was clustered with the molluscan subgroup in STAT5 clade with distinct evolution. According to the genomic structure of AbSTAT5, the coding sequence was distributed into 20 exons with 19 introns. Immunologically essential transcription factor-binding sites, such as GATA-1, HNF, SP1, C/EBP, Oct-1, AP1, c-Jun, and Sox-2, were predicted at the 5'-proximal region of AbSTAT5. Expression of AbSTAT5 mRNA was detected in different stages of embryonic development and observed at considerably higher levels in the morula and late veliger stages. Tissue-specific expressional studies revealed that the highest level of AbSTAT5 transcripts was detected in hemocytes, followed by gill tissues. Temporal expressions of AbSTAT5 were analyzed upon live bacterial (Vibrio parahemolyticus and Listeria monocytogenes), viral (viral hemorrhagic septicemia virus), and pathogen-associated molecular pattern (lipopolysaccharides and Poly I:C) stimulations, and significant elevations indicated immune modulation. These results suggest that AbSTAT5 may be involved in maintaining innate immune responses from developmental to adult stages in the disk abalone. Further, this study provides a basis for structural and functional exploration of STAT members in the invertebrate JAK/STAT signaling pathway.

Two variants of selenium-dependent glutathione peroxidase from the disk abalone Haliotis discus discus: Molecular characterization and immune responses to bacterial and viral stresses

Glutathione peroxidase (GPx) is an essential member of the antioxidant systems of living organisms and may be involved in immune defense against pathogenic invasion. In the current study, two selenium-dependent glutathione peroxidases (AbSeGPxs) that shared 54.3% identity were identified from the disk abalone Haliotis discus discus. The open reading frames (ORFs) of AbSeGPx-a and AbSeGPx-b coded for 222 and 220 amino acids, respectively, with a characteristic selenocysteine residue encoded by an opal stop codon (TGA). The conserved selenocysteine insertion sequence (SECIS) element was predicted in the 3' untranslated region (UTR) of both isoforms, and they were found to form two stem-loop structures. Amino acid comparison and phylogenetic studies revealed that the AbSeGPxs were closely related to those in other mollusk species and were evolutionarily distinct from those of other taxonomic groups. The SYBR Green qPCR was employed in investigating the transcripts of AbSeGPxs. The expression of AbSeGPxs mRNA was examined in different embryonic developmental stages and differential expression patterns for AbSeGPx-a and AbSeGPx-b were noted. Meanwhile, the highest expression of AbSeGPxs was detected in the hepatopancreas of healthy adult animals. Next, transcriptional levels were profiled in hemocytes of adults to determine the immune responses of AbSeGPxs to microbial infections. The results revealed the significant up-regulation of AbSeGPx-a in a time-dependent manner after bacterial (Listeria monocytogenes and Vibrio parahaemolyticus) and viral (viral hemorrhagic septicemia virus) infections. Consequently, these findings indicate that AbSeGPx-a and AbSeGPx-b might be involved in the embryonic development of disk abalone and the regulation of immune defense system of adult animals.

Three novel clade B serine protease inhibitors from disk abalone, Haliotis discus discus: Molecular perspectives and responses to immune challenges and tissue injury

Serine protease inhibitors (SERPINs) control cellular protease activity in order to maintain cellular homeostasis. The immune and inflammatory responses of invertebrate clade B SERPINs have not been widely reported. In the present study, three proteins with high similarity to clade B SERPINs, referred to as AbSERPIN-1, AbSERPIN-2 and AbSERPIN-3, were identified from disk abalone (Haliotis discus discus). While AbSERPIN-1 (399 aa) was of a typical size for this protein class, AbSERPIN-2 (506 aa) and AbSERPIN-3 (532 aa) were relatively larger. Bioinformatic analysis revealed the characteristic SERPIN domain in each AbSERPIN. In addition, the N-terminal region of both AbSERPIN-2 and AbSERPIN-3 contained a predicted low complexity region (LCR) and a signal peptide, suggesting that these proteins are secretory proteins and are, thus, novel peptides. Tertiary structural models of the AbSERPINs highlighted their structural and functional conservation. Ubiquitous expression of AbSERPIN transcripts was evaluated by quantitative real time PCR (qPCR) analysis in seven tissue types. AbSERPIN-1, AbSERPIN-2, and AbSERPIN-3 transcript levels were highest in mantle, hemocytes, and muscles, respectively. Temporal expression analysis revealed that AbSERPINs were significantly (P < 0.05) elevated in hemocytes during the early/middle stages following the injection of a bacterial pathogen (Vibrio parahaemolyticus or Listeria monocytogenes) or an immuno-stimulant (lipopolysaccharide). Moreover, mantle tissue injury led to significant changes in the temporal expression of AbSERPIN mRNA. Specifically, transcription of AbSERPIN-1 and AbSERPIN-3 was considerably up-regulated, while expression of AbSERPIN-2 was suppressed. These results suggest a potential role of AbSERPINs in response to pathogen invasion and tissue injury in disk abalone.

Antibacterial activity and immune responses of a molluscan macrophage expressed gene-1 from disk abalone, Haliotis discus discus

The membrane-attack complex/perforin (MACPF) domain-containing proteins play an important role in the innate immune response against invading microbial pathogens. In the current study, a member of the MACPF domain-containing proteins, macrophage expressed gene-1 (MPEG1) encoding 730 amino acids with the theoretical molecular mass of 79.6 kDa and an isoelectric point (pI) of 6.49 was characterized from disk abalone Haliotis discus discus (AbMPEG1). We found that the characteristic MACPF domain (Val(131)-Tyr(348)) and transmembrane segment (Ala(669)-Ile(691)) of AbMPEG1 are located in the N- and C-terminal ends of the protein, respectively. Ortholog comparison revealed that AbMPEG1 has the highest sequence identity with its pink abalone counterpart, while sequences identities of greater than 90% were observed with MPEG1 members from other abalone species. Likewise, the furin cleavage site KRRRK was highly conserved in all abalone species, but not in other species investigated. We identified an intron-less genomic sequence within disk abalone AbMPEG1, which was similar to other mammalian, avian, and reptilian counterparts. Transcription factor binding sites, which are important for immune responses, were identified in the 5'-flanking region of AbMPEG1. qPCR revealed AbMPEG1 transcripts are present in every tissues examined, with the highest expression level occurring in mantle tissue. Significant up-regulation of AbMPEG1 transcript levels was observed in hemocytes and gill tissues following challenges with pathogens (Vibrio parahemolyticus, Listeria monocytogenes and viral hemorrhagic septicemia virus) as well as pathogen-associated molecular patterns (PAMPs: lipopolysaccharides and poly I:C immunostimulant). Finally, the antibacterial activity of the MACPF domain was characterized against Gram-negative and -positive bacteria using a recombinant peptide. Taken together, these results indicate that the biological significance of the AbMPEG1 gene includes a role in protecting disk abalone through the ability of AbMPEG1 to initiate an innate immune response upon pathogen invasion.

Evidences for the involvement of an invertebrate goose-type lysozyme in disk abalone immunity: cloning, expression analysis and antimicrobial activity

Lysozymes are ubiquitously distributed enzymes with hydrolytic activity against bacterial peptidoglycan and function to protect organisms from microbial pathogens. In this study, an invertebrate goose-type lysozyme, designated as abLysG, was identified in the disk abalone, Haliotis discus discus. The full-length cDNA of abLysG was 894 bp in length with an open reading frame of 789 bp encoding a polypeptide of 263 amino acids containing a signal peptide and a characteristic soluble lytic transglycosylase domain. Six cysteine residues and two catalytic residues (Glu(142) and Asp(168)) conserved among molluscs were also identified. The 3D homology structural models of abLysG and hen egg white lysozyme had similar conformations of the active sites involved in the binding of substrate. BAC sequence data revealed that the genomic structure of disk abalone g-type lysozyme comprises 7 exons with 6 intervening introns. The deduced amino acid sequence of abLysG shared 45.2-61.6% similarity with those of other molluscs and vertebrates. The TFSEARCH server predicted a variety of transcription factor-binding sites in the 5'-flanking region of the abLysG gene, some of which are involved in transcriptional regulation of the lysozyme gene. abLysG expression was detected in multiple tissues with the highest expression in mantle. Moreover, qPCR analysis of abLysG mRNA expression demonstrated significant up-regulation in gill in response to infection by live bacteria (Vibrio parahaemolyticus and Listeria monocytogenes), virus (viral hemorrhagic septicemia) and bacterial mimics (LPS and PGN). Expression of the recombinant disk abalone g-type lysozyme in Escherichia coli BL21, demonstrated its bacteriolytic activity against several Gram-negative and Gram-positive bacterial species. Collectively these data suggest that abLysG is an antimicrobial enzyme with a potential role in the disk abalone innate immune system to protect it from bacterial and viral infections.

Two duplicated chicken-type lysozyme genes in disc abalone Haliotis discus discus: molecular aspects in relevance to structure, genomic organization, mRNA expression and bacteriolytic function

Lysozymes are crucial antibacterial proteins that are associated with catalytic cleavage of peptidoglycan and subsequent bacteriolysis. The present study describes the identification of two lysozyme genes from disc abalone Haliotis discus discus and their characterization at sequence-, genomic-, transcriptional- and functional-levels. Two cDNAs and BAC clones bearing lysozyme genes were isolated from abalone transcriptome and BAC genomic libraries, respectively and sequences were determined. Corresponding deduced amino acid sequences harbored a chicken-type lysozyme (LysC) family profile and exhibited conserved characteristics of LysC family members including active residues (Glu and Asp) and GS(S/T)DYGIFQINS motif suggested that they are LysC counterparts in disc abalone and designated as abLysC1 and abLysC2. While abLysC1 represented the homolog recently reported in Ezo abalone [1], abLysC2 shared significant identity with LysC homologs. Unlike other vertebrate LysCs, coding sequence of abLysCs were distributed within five exons interrupted by four introns. Both abLysCs revealed a broader mRNA distribution with highest levels in mantle (abLysC1) and hepatopancreas (abLysC2) suggesting their likely main role in defense and digestion, respectively. Investigation of temporal transcriptional profiles post-LPS and -pathogen challenges revealed induced-responses of abLysCs in gills and hemocytes. The in vitro muramidase activity of purified recombinant (r) abLysCs proteins was evaluated, and findings indicated that they are active in acidic pH range (3.5-6.5) and over a broad temperature range (20-60 °C) and influenced by ionic strength. When the antibacterial spectra of (r)abLysCs were examined, they displayed differential activities against both Gram positive and Gram negative strains providing evidence for their involvement in bacteriolytic function in abalone physiology.

Genomic characterization and expression profiles upon bacterial infection of a novel cystatin B homologue from disk abalone (Haliotis discus discus)

Cystatins are a large family of cysteine proteinase inhibitors which are involved in diverse biological and pathological processes. In the present study, we identified a gene related to cystatin superfamily, AbCyt B, from disk abalone Haliotis discus discus by expressed sequence tag (EST) analysis and BAC library screening. The complete cDNA sequence of AbCyt B is comprised of 1967 nucleotides with a 306 bp open reading frame (ORF) encoding for 101 amino acids. The amino acid sequence consists of a single cystatin-like domain, which has a cysteine proteinase inhibitor signature, a conserved Gly in N-terminal region, QVVAG motif and a variant of PW motif. No signal peptide, disulfide bonds or carbohydrate side chains were identified. Analysis of deduced amino acid sequence revealed that AbCyt B shares up to 44.7% identity and 65.7% similarity with the cystatin B genes from other organisms. The genomic sequence of AbCyt B is approximately 8.4 Kb, consisting of three exons and two introns. Phylogenetic tree analysis showed that AbCyt B was closely related to the cystatin B from pacific oyster (Crassostrea gigas) under the family 1.Functional analysis of recombinant AbCyt B protein exhibited inhibitory activity against the papain, with almost 84% inhibition at a concentration of 3.5 μmol/L. In tissue expression analysis, AbCyt B transcripts were expressed abundantly in the hemocyte, gill, mantle, and digestive tract, while weakly in muscle, testis, and hepatopancreas. After the immune challenge with Vibrio parahemolyticus, the AbCyt B showed significant (P<0.05) up-regulation of relative mRNA expression in gill and hemocytes at 24 and 6 h of post infection, respectively. These results collectively suggest that AbCyst B is a potent inhibitor of cysteine proteinases and is also potentially involved in immune responses against invading bacterial pathogens in abalone.

Gene expression patterns and stress response in marine copepods

Aquatic organisms are constantly exposed to both physical (e.g. temperature and salinity variations) and chemical (e.g. endocrine disruptor chemicals, heavy metals, hydrocarbons, diatom toxins, and other toxicants) stressors which they react to by activating a series of defense mechanisms. This paper reviews the literature on the defense systems, including detoxification enzymes and proteins (e.g. glutathione S-transferases, heat shock proteins, superoxide dismutase and catalase), studied in copepods at the molecular level. The data indicate high inter- and intra-species variability in copepod response, depending on the type of stressor tested, the concentration and exposure time, and the enzyme isoform studied. Ongoing -omics approaches will allow the identification of new genes which will give a more comprehensive overview of how copepods respond to specific stressors in laboratory and/or field conditions and the effects of these responses on higher trophic levels.

Characterization of a cytochrome P450 gene (CYP4G) and modulation under different exposures to xenobiotics (tributyltin, nonylphenol, bisphenol A) in Chironomus riparius aquatic larvae

Cytochrome P450 family members participate in xenobiotic transformation as a detoxification mechanism. We have characterized a CYP gene, assigned to the 4G family, in Chironomus riparius, a reference organism in aquatic toxicology. Due to the potential interest of CYP genes and P450 proteins for monitoring pollution effects at the molecular level, the alterations in the pattern of expression of this gene, induced by different xenobiotics, were analyzed. Different compounds, such as the biocide tributyltin (TBTO) and two other well-known endocrine disruptors, nonylphenol (NP) and bisphenol A (BPA), were tested at different concentrations and acute exposures. Upregulation of the CrCYP4G gene was found after exposures to TBTO (1 ng/L 24h-0.1 ng/L 96 h) and, as measured by RT-PCR mRNA quantification, its level was up to twofold that of controls. However, in contrast, NP (1, 10, 100 μg/L, 24h) and BPA (0.5mg/L 24h-3mg/L 96 h) downregulated the gene (by around a half of the control level) suggesting that this gene responds specifically to particular chemicals in the environment. Glutathione-S-transferase (GST) enzymatic activity was also evaluated for each condition. A fairly good correlation was found with CYP4G gene behavior, as it was activated by TBTO (96 h), but inhibited by NP and BPA (24h). Only the higher concentration of BPA tested activated GST, whereas it inhibited CYP4G activity. The results show that different xenobiotics can induce distinct responses in the detoxification pathway, suggesting multiple xenobiotic transduction mechanisms. This work confirms that specific P450 codifying genes, as well as GST enzyme activities, could be suitable biomarkers for ecotoxicological studies.

Molecular evidence of the toxic effects of diatom diets on gene expression patterns in copepods

BACKGROUND

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy through marine food chains. However, these unicellular plants at times produce secondary metabolites such as polyunsaturated aldehydes and other products deriving from the oxidation of fatty acids that are collectively termed oxylipins. These cytotoxic compounds are responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment in marine organisms such as crustacean copepods.

PRINCIPAL FINDINGS

Here we show that two days of feeding on a strong oxylipin-producing diatom (Skeletonema marinoi) is sufficient to inhibit a series of genes involved in aldehyde detoxification, apoptosis, cytoskeleton structure and stress response in the copepod Calanus helgolandicus. Of the 18 transcripts analyzed by RT-qPCR at least 50% were strongly down-regulated (aldehyde dehydrogenase 9, 8 and 6, cellular apoptosis susceptibility and inhibitor of apoptosis IAP proteins, heat shock protein 40, alpha- and beta-tubulins) compared to animals fed on a weak oxylipin-producing diet (Chaetoceros socialis) which showed no changes in gene expression profiles.

CONCLUSIONS

Our results provide molecular evidence of the toxic effects of strong oxylipin-producing diatoms on grazers, showing that primary defense systems that should be activated to protect copepods against toxic algae can be inhibited. On the other hand other classical detoxification genes (glutathione S-transferase, superoxide dismutase, catalase, cytochrome P450) were not affected possibly due to short exposure times. Given the importance of diatom blooms in nutrient-rich aquatic environments these results offer a plausible explanation for the inefficient use of a potentially valuable food resource, the spring diatom bloom, by some copepod species.