Receptor activated C kinase is down-regulated in the male gonad of the marine bivalve mollusc Mya arenaria exposed to tributyltin (TBT)

Molecular Cloning, Characterization, and Expression of a Receptor for Activated Protein Kinase C1 (RACK1) Gene in Exopalaemon carinicauda Zoea Larvae under Aroclor 1254 Stress

The receptor for activated protein kinase C1 (RACK1) belongs to the typical WD repeat family, which is extremely conservative and important in multiple signal transduction pathways related to growth and development that coordinate the intracellular role of various life activities. As a novel protein with versatile functions, it was found in a variety of organisms. In a previous study, we identified the RACK1 sequence of white shrimp from transcriptome data. In this study, we employed specialized bioinformatics software to conduct an in-depth analysis of EcRACK1 and compare its amino acid sequence homology with other crustaceans. Furthermore, we investigated the expression patterns of RACK1 at different developmental stages and tissues, as well as at various time points after exposure to Aroclor 1245, aiming to elucidate its function and potential response towards Aroclor 1245 exposure. The length of EcRACK1 is 957 nucleotides, which encodes 318 amino acids. Moreover, there were seven typical WD repeats in EcRACK1, which have more than a 96% sequence identity with the RACK1 proteins of Penaeus. The results of tissue expression and spatiotemporal expression showed that it was significantly increased in the II and IV stages, but had a significant tissue specificity in the hepatopancreas, spermary, and muscle tissues of E. carinicauda, adult stage. Compared to the control, EcRACK1 was significantly induced in E. carinicauda zoea larvae exposed to Aroclor 1254 for 6, 10, 20, and 30 d (p < 0.05). These results suggested that EcRACK1 may play an important role in the larval development and environmental defense of E. carinicauda.

Characterization of the RACK1 gene of Aips cerana cerana and its role in adverse environmental stresses

Receptors for Activated C Kinase 1 (RACK1s) are a kind of multifunction scaffold protein that plays an important role in cell signal transductions and animal development. However, the function of RACK1 in the Chinese honeybee Apis cerana cerana is little known. Here, we isolated and identified a RACK1 gene from Apis cerana cerana, named AccRACK1. By bioinformatic analysis, we revealed a high nucleic acid homology between AccRACK1 and RACK1 of Apis cerana. RT-qPCR analyses demonstrated AccRACK1 was mostly expressed in 3rd instar larvae, darked-eyed pupae and adults (one and thirty days post-emergence), suggesting it might participate in the development of A. cerana cerana. Moreover, the expression of AccRACK1 was highest in the thorax, followed by the venom gland. Compared to the blank control group, AccRACK1 was induced by 24 and 44 °C, HgCl2 and pesticides (paraquat, pyridaben and methomyl) but inhibited by 14 °C, H2O2, UV light and cyhalothrin. Additionally, 0.05, 0.1, 1, 5 and 10 mg/ml PPN (juvenile hormone analogue pyriproxyfen) could promote the expression of AccRACK1, with 1 mg/ml showing the highest upregulation, suggesting it was regulated by hormones. Further study found that after knockdown of AccRACK1 by RNAi, the expression of the eukaryotic initiation factor 6 of A. cerana cerana (AcceIF6), an initiation factor regulating the initiation of translation, was inhibited, indicating AccRACK1 might affect cellular responses by translation. These findings, taken together, suggest AccRACK1 is involved in the development and responses to abiotic stresses of A. cerana cerana, and therefore, it may be of critical importance to the survival of A. cerana cerana.

Global expression response of genes in sex-undifferentiated Nile tilapia gonads after exposure to trace letrozole

The aromatase inhibitor letrozole can be found in rivers, effluents, and even drinking water. Studies have demonstrated that letrozole affects various metabolic pathways and may cause reproductive toxicity, especially in fish exposed during development. However, studies on the effect of a low concentration of letrozole at the whole-gonad transcriptomic level in the early stage of fish sexual development have not been investigated. The aim of our study was to explore the potential effects of a low concentration of letrozole on the gonad transcriptome of Nile tilapia at an early stage of sexual development. In this study, 9 dpf (days postfertilization) Nile tilapia were exposed to trace letrozole for 12 days. Letrozole exposure from 9 dpf to 21 dpf persistently altered phenotypic sex development and induced the male-biased sex ratio. The transcriptome results showed that 1173 differentially expressed genes (DEGs) were present in the female control vs 1.5 μg/L letrozole-treated female comparison group and that 1576 DEGs were present in the 1.5 μg/L letrozole-treated female vs male control comparison group. Differentially expressed gene enrichment analysis revealed several crucial pathways, including the drug metabolism-cytochrome P450 pathway, the ErbB-PI3K/Akt/mTOR pathway, and the calcium signalling pathway. Further analysis of these identified DEGs indicated that some key genes correlated with metabolism and epigenetic regulation were significantly affected by letrozole, such as UDP-glucuronosyltransferase (Ugt), glutathione S-transferase omega-1 (Gsto1), lysine-specific demethylase 6bb (Kdm6bb, original name is Kdm6a), jumonji and AT-rich interaction domain containing 2 (Jarid2b, original name is Jarid2), growth arrest and DNA damage inducible gamma (Gadd45g), and chromobox protein 7 (Cbx7). The qRT-PCR validation results for twelve DEGs showed that the Pearson's correlation of the log₁₀^{fold change} values between the qPCR and RNA-Seq results was 0.90, indicating the accuracy and reliability of the RNA-Seq results. Our study is the first to report the effect of letrozole on the transcriptome of gonads from fish during early-stage sexual development. These findings will be useful for understanding the toxic effects and molecular mechanisms of letrozole exposure at the early stage of gonad development on the sexual development of aquatic organisms.

The receptor for activated C kinase 1 (RACK1) mediating immune response in thick shell mussel Mytilus coruscus

The receptor for activated C kinase 1 (RACK1) is a intracellular receptor for the protein kinase C family which mediates various biological processes. Here, a novel RACK1 gene termed Mc-RACK1 was identified from thick shell mussel, Mytilus coruscus. Mc-RACK1 shared typical RACK1 domains containing WD repeats, PKC phosphorylation sites, N-myristoylation sites, PKC activation sites, TK phosphorylation site and WD motifs. Mc-RACK1 was constitutively expressed in all examined tissues, and its expression in gills, haemocytes and digestive glands were significantly up-regulated upon LPS challenge. Mc-RACK1 showed a significantly down-regulated expression in gills and haemocytes at the early phase upon copper exposure. Mc-RACK1 in haemocytes was silenced after receiving its dsRNA, meanwhile, the increases of SOD and CAT activity were investigated. Further, Mc-RACK1 could activate the NF-κB and ISRE reporter in HEK-293T cells. These suggested that Mc-RACK1 had a deeper involvement in mollusc immunity, and played an important role in antioxidant system.

Imposex in Nassarius nitidus (Jeffreys, 1867) as a possible investigative tool to monitor butyltin contamination according to the Water Framework Directive: A case study in the Venice Lagoon (Italy)

Butyltin (TBT, DBT, and MBT) effects on molluscs, especially endocrine disruption in bivalves and gastropods, have been widely investigated. Imposex, the superimposition of male characters onto female gonochoristic Caenogastropods, is the most studied biological effect of TBT. TBT compounds are among the priority hazardous substances within Directives 2000/60/EC (WFD) and 2008/105/EC. The Environmental Quality Standards (EQSs) set by the WFD for TBT are quite difficult to quantify by means of chemical analysis, without the use of expensive and high performance methods. Assuming that EQSs set for TBT were derived from evidence of imposex development at very low concentrations, this specific biomarker could be used as an indirect measure of assessing levels of bioavailable BTs. Therefore, this study aims to validate the use of imposex development as an investigative tool to monitor the bioavailable fraction of BTs within the WFD, by comparing imposex levels and BT concentrations in Nassarius nitidus from the Venice Lagoon. BT concentrations and imposex levels in N. nitidus, collected in 2013, had decreased when compared to previous studies in the same area. Both VDSI and RPLI correlated positively with BT body burden in females, confirming that imposex is a valid tool to monitor bioavailable BTs. However, TBT is still a matter of concern in the Venice Lagoon, as TBT concentrations were still higher than its degradation products suggesting recent fresh TBT inputs in the studied area. To propose imposex levels as an indicator of the impact of BTs within the WFD, classification class boundaries and Ecological Quality Ratios were introduced. As a preliminary attempt, imposex levels were also compared to the OSPAR Commission EcoQOs which linked imposex levels in Nassarius reticulatus with TBT concentrations in water. Based on this comparison the degree of imposex development in the Venice Lagoon suggested that TBT concentrations in water should be over the EQS-AA concentration and, at one site, also over the EQS-MAC. From all the results obtained in this work, it appears that imposex evaluation in N. reticulatus could give information about the ecological status regarding BT compounds under the WFD and also be used to monitor their effects and support chemical analyses until more sensitive methods become available.

Identification of interacting proteins with aryl hydrocarbon receptor in scallop Chlamys farreri by yeast two hybrid screening

The aryl hydrocarbon receptor (AhR) belongs to the basic-helix-loop helix (bHLH) Per-Arnt-Sim (PAS) family of transcription factors. AhR has been known primarily for its role in the regulation of several drug and xenobiotic metabolizing enzymes, as well as the mediation of the toxicity of certain xenobiotics, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Although the AhR is well-studied as a mediator of the toxicity of certain xenobiotics in marine bivalves, the normal physiological function remains unknown. In order to explore the function of the AhR, the bait protein expression plasmid pGBKT7-CfAhR and the cDNA library of gill from Chlamys farreri were constructed. By yeast two hybrid system, after multiple screening with the high screening rate medium, rotary verification, sequencing and bioinformatics analysis, the interactions of the CfAhR with receptor for activated protein kinase C 1 (RACK1), thyroid peroxidase-like protein (TPO), Toll-like receptor 4(TLR 4), androglobin-like, store-operated Ca(2+) entry (SocE), ADP/ATP carrier protein, cytochrome b, thioesterase, actin, ferritin subunit 1, poly-ubiquitin, short-chain collagen C4-like and one hypothetical protein in gill cells were identified. This study suggests that the CfAhR played fundamental roles in immune system homeostasis, oxidative stress response, and in grow and development of C. farreri. The elucidation of these protein interactions is of much importance both in understanding the normal physiological function of AhR, and as potential targets for further research on protein function in AhR interactions.

The receptor for activated C kinase 1 (RACK1) functions in hematopoiesis through JNK activation in Chinese mitten crab Eriocheir sinensis

Receptor for activated C kinase 1 (RACK1) is a WD-domain repeating protein which involves in the mediation of various biological processes, including innate immune response. In the present study, a RACK1 (designed as EsRACK1) gene from Chinese mitten crab E. sinensis was cloned by rapid amplification of cDNA ends (RACE) technique. The full-length cDNA sequence of EsRACK1 was of 1117 bp with an open reading frame (ORF) of 957 bp encoding a polypeptide of 318 amino acids containing seven WD repeats. EsRACK1 shared 62%-99% similarities with previously identified RACK1s in amino acid sequence, and it was clustered with the RACK1 from Pacifastacus leniusculus in the phylogenetic tree. The mRNA transcripts of EsRACK1 were constitutively expressed in various tissues with the highest expression level in hepatopancreas. The expression of EsRACK1 mRNA in hemocytes were significantly up-regulated post the stimulations with Vibrio anguillarum and Pichia pastoris. After exposure to CdCl2 and pentachlorophenol, the transcripts of EsRACK1 in hemocytes were up-regulated at the late phase from 12 h. When EsRACK1 was knocked down by dsRNA based RNAi, the total hemocyte counts, new-born hemocytes and phosphorylation of JNK were all significantly decreased. In addition, EsRACK1 transcription and phosphorylation of JNK were both decreased in hematopoietic tissue post Aeromonas hydrophila challenge. All the results suggested that EsRACK1 was involved in the innate immune response of the crab and participated in the production of new-born hemocytes through activation of JNK.

Intersex related gene expression profiles in clams Scrobicularia plana: Molecular markers and environmental application

Intersex, the appearance of female characteristics in male gonads, has been identified in several aquatic species. It is a widespread phenomenon in populations of the bivalve, Scrobicularia plana, from the southwest coast of the U.K. Genes previously identified as differentially expressed (ferritin, testicular haploid expressed gene, THEG, proliferating cell nuclear antigen, PCNA; receptor activated protein kinase C, RACK; cytochrome B, CYB; and cytochrome c oxidase 1, COX1) in intersex clams relative to normal male clams, were selected for characterisation and an environmental survey of the Channel region. Transcripts were significantly differentially expressed at sites with varying intersex incidence and contaminant burdens. Significant correlations between specific gene expressions, key contaminants and sampling locations have been identified, though no single gene was associated with intersex incidence. The results highlight the difficulty in understanding the intersex phenomenon in molluscs where there is still a lack of knowledge on the control of normal reproduction.

Intersex in Scrobicularia plana: transcriptomic analysis reveals novel genes involved in endocrine disruption

Intersex, the appearance of female characteristics in male gonads, has been identified in a wide range of aquatic species worldwide, yet the underpinning molecular etiology remains uncharacterized. The presence of intersex has been shown to be a widespread phenomenon in bivalve, S. plana, populations from the southwest coast of the U.K., as well as inducible in an experimental exposure regime using endocrine disrupting compounds (EDCs). Herein, we use the suppressive subtractive hybridization approach to isolate differentially expressed transcripts in S. plana males exhibiting intersex. Transcripts involved in cell signaling, cell cycle control, energy production/metabolism, microtubule assembly, and sperm physiology are all highlighted as differentially expressed in intersex male clams. These provide both an insight into the molecular mechanisms of action involved in the development of intersex, as well as facilitating potential molecular-level "early warning" biomarkers of the condition.

Molecular cloning, characterization and expression analysis of receptor for activated C kinase 1 (RACK1) from pearl oyster (Pinctada martensii) challenged with bacteria and exposed to cadmium

Receptor for activated C kinase 1 (RACK1) is involved in superoxide anion generation and play an important role in the immune response. In the study, we cloned the full-length sequence of pearl oyster, Pinctada martensii, RACK1 (designated as PmRACK1) by a combination of expression sequence tag (EST) analysis and rapid amplification of cDNA ends (RACE). The full-length cDNA of PmRACK1 is 1176 bp in length, containing a 5' UTR of 83 bp, a 3' UTR of 139, and an open reading frame (ORF) of 954 bp encoding 317 amino acids. Analysis of protein domain features showed that the deduced polypeptide contain seven WD domains characteristic of RACK1 protein family. The tissue distribution of PmRACK1 in unchallenged pearl oysters and temporal expression pattern of PmRACK1 in pearl oysters challenged with bacteria and exposed to 0.1 ppm cadmium were analyzed by quantitative real-time PCR (qRT-PCR). The transcript was detected in all tissues tested, and the expression level was highest in hepatopancreas and lowest in adductor muscle. After challenge with bacteria, expression level of PmRACK1 in haemocytes was gradually decreased until 6 h post challenge, and then up-regulated over time. After exposure to cadmium, its expression level in gill decreased on 1 d post exposure, and then increased as time elapsed, and its expression level in hepatopancreas gradually decreased until 2 d post exposure, and then increased over time. These results suggested that PmRACK1 was involved in oxidative stress response caused by bacteria and cadmium and was a useful biomarker for cadmium exposure. The expression pattern of PmRACK1 in response to bacterial challenge also has a potential link with organism's immune response.

Effects of pesticide compounds (chlorothalonil and mancozeb) and benzo[a]pyrene mixture on aryl hydrocarbon receptor, p53 and ubiquitin gene expression levels in haemocytes of soft-shell clams (Mya arenaria)

The aim of this study is to investigate the effects of the pesticides/polycyclic aromatic hydrocarbon mixture on aryl hydrocarbon receptor (AhR), p53 and ubiquitin mRNA level in haemocytes of Mya arenaria exposed to a mixture of chlorothalonil, mancozeb and benzo[a]pyrene (BaP) for 48 and 72 h. AhR, p53 and ubiquitin gene expression levels were quantified using quantitative Real-time PCR. For robust and accurate quantification of transcripts, suitable housekeeping genes were selected from four sets of ribosomal and elongation factors transcripts previously sequenced from Mya arenaria using geNorm open source software. Quantitative Real-time PCR data exhibited a significantly high expression of AhR after 72 h of exposure (P ≤ 0.05). p53 gene expression seems to be up-regulated by the mixture after 48 h, however not significantly; but the level of p53 mRNA is down-regulated by the xenobiotics between 48 and 72 h after exposure. This study postulates that AhR mRNA levels could be used as an indicator of the exposure of clams' haemocytes to a mixture of xenobiotics such as chlorothalonil, mancozeb and BaP. However, further studies have to be pursued in order to unravel the molecular mechanisms involved in the p53 signaling pathway.

Gene expression profiling in respond to TBT exposure in small abalone Haliotis diversicolor

In this study, we investigated the gene expression profiling of small abalone, Haliotis diversicolor by tributyltin (TBT) exposure using a cDNA microarray containing 2473 unique transcripts. Totally, 107 up-regulated genes and 41 down-regulated genes were found. For further investigation of candidate genes from microarray data and EST analysis, quantitative real-time PCR was performed at 6 h, 24 h, 48 h, 96 h and 192 h TBT exposure. 26 genes were found to be significantly differentially expressed in different time course, 3 of them were unknown. Some gene homologues like cellulose, endo-beta-1,4-glucanase, ferritin subunit 1 and thiolester containing protein II CG7052-PB might be the good biomarker candidate for TBT monitor. The identification of stress response genes and their expression profiles will permit detailed investigation of the defense responses of small abalone genes.

Differential gene expression of gamma-actin, Toll-like receptor 2 (TLR-2) and interleukin-1 receptor-associated kinase 4 (IRAK-4) in Mya arenaria haemocytes induced by in vivo infections with two Vibrio splendidus strains

Immune function gene expression in Mya arenaria haemocytes was evaluated following in vivo infection with Vibrio splendidus LGP32-GFP and 7SHRW. Elongation factor 1alpha (EF-1alpha) with 2 (EF-2), after challenge with LGP32-GFP, and EF-1alpha with the ribosomal protein S-18, after challenge with 7SHRW, were found to be the most stable housekeeping genes. Using these internal controls and comparing the regulation induced by both strains, up-regulation of gamma-actin, down-regulation of TLR-2 and up-regulation of IRAK-4 was significantly higher after challenge with LGP32-GFP (p<0.001, p=0.001 and p<0.05, respectively). These results suggest specific responses at a molecular level modulated by the bacterial strains. LGP32-GFP induced marked responses which coincide with a similar trend previously found on phenotypic responses under our experimental model.

Spreading by snail (Lymnaea stagnalis) defence cells is regulated through integrated PKC, FAK and Src signalling

Cell adhesion and spreading are vital to immune function. In molluscs, haemocytes (circulating phagocytes) are sentinels and effectors of the internal defence system; however, molecular mechanisms that regulate integrin-mediated spreading by haemocytes have not been characterised in detail. Visualisation of Lymnaea stagnalis haemocytes by scanning electron microscopy revealed membrane ruffling, formation of lamellipodia and extensive filopodia during early stages of cell adhesion and spreading. These events correlated with increased phosphorylation (activation) of protein kinase C (PKC) and focal adhesion kinase (FAK), sustained for 60 min. Treatment of haemocytes with the PKC inhibitors GF109203X or Gö 6976, or the Src/tyrosine kinase inhibitors SrcI or herbimycin A, attenuated haemocyte spread by 64, 46, 32 and 35%, respectively (P <or= 0.001); PKC or Src inhibition also prevented focal adhesion formation. Western blotting demonstrated that during spreading and adhesion these inhibitors also impaired PKC and FAK activation, with Gö 6976 or SrcI inhibiting FAK phosphorylation by at least 70% (P <or= 0.001), and herbimycin A or SrcI inhibiting PKC phosphorylation by at least 46% (P <or= 0.01). Confocal microscopy revealed phosphorylated PKC colocalised with focal adhesion sites, particularly during early phases of adhesion and spreading. Finally, fibronectin promoted PKC and FAK phosphorylation in suspended haemocytes demonstrating that activation can occur independent of cell adhesion. These novel data are consistent with PKC and FAK/Src playing an integrated role in integrin activation and integrin-mediated spreading by L. stagnalis haemocytes. We propose a model in which integrin engagement mediates association of PKC with FAK/Src complexes to promote focal adhesion assembly during immune recognition by these cells.

Peroxisomal proteomics: biomonitoring in mussels after the Prestige's oil spill

Peroxisomal proteomics was applied to assess possible biological effects after the Prestige's oil spill. Mussels were sampled in July 2004 and 2005 in four stations in the NW (closest to the spill) and NE coasts of the Iberian Peninsula. Principal components analysis (PCA) suggested differences in protein expression among stations and sampling years. Several proteins were putatively identified by mass spectrometry and immunolocalization. PC1 separated the NW stations in 2004 from the rest of the stations and sampling years mainly due to up-regulation of peroxisomal beta-oxidation proteins and PMP70. PC3 separated the NE stations, based on up-regulation of the antioxidant enzyme catalase in 2004 compared to 2005. PC4 separated the stations in the NE and the NW. This work shows that environmental proteomics, together with multivariate data analysis, could provide information to interpret the effects of oil spills at cellular level in mussels.

Identification and expression of differentially expressed genes in the hard clam, Mercenaria mercenaria, in response to quahog parasite unknown (QPX)

Background

The hard clam, Mercenaria mercenaria, has been affected by severe mortality episodes associated with the protistan parasite QPX (Quahog Parasite Unknown) for several years. Despite the commercial importance of hard clams in the United States, molecular bases of defense mechanisms in M. mercenaria, especially during QPX infection, remain unknown.

Results

Our study used suppression subtractive hybridization (SSH), as well as the construction of cDNA libraries from hemocytes to identify genes related to the defense of the hard clam against its parasite. Hard clams were experimentally infected with QPX and SSH was performed on mRNA samples extracted from mantle and gill tissues at different times post-challenge. A total of 298 clones from SSH libraries and 1352 clones from cDNA libraries were sequenced. Among these sequences, homologies with genes involved in different physiological processes related to signal transduction, stress response, immunity and protein synthesis were identified. Quantitative PCR revealed significant changes in the expression of several of these genes in response to QPX challenge and demonstrated significant correlations in terms of levels of gene expression between intermediates of signalling pathways and humoral defense factors, such as big defensin and lysozyme.

Conclusion

Results of this study allowed the detection of modifications caused by QPX at the transcriptional level providing insight into clam immune response to the infection. These investigations permitted the identification of candidate genes and pathways for further analyses of biological bases of clam resistance to QPX allowing for a better understanding of bivalve immunity in general.

Range-wide genetic homogeneity in the California sea mussel (Mytilus californianus): a comparison of allozymes, nuclear DNA markers, and mitochondrial DNA sequences

We tested for genetic differentiation among six populations of California sea mussels (Mytilus californianus) sampled across 4000 km of its geographical range by comparing patterns of variation at four independent types of genetic markers: allozymes, single-copy nuclear DNA markers, and DNA sequences from the male and female mitochondrial genomes. Despite our extensive sampling and genotyping efforts, we detected no significant differences among localities and no signal of isolation by distance suggesting that M. californianus is genetically homogeneous throughout its range. This concordance differs from similar studies on other mytilids, especially in the role of postsettlement selection generating differences between exposed coastal and estuarine habitats. To assess if this homogeneity was due to M. californianus not inhabiting estuarine environments, we reviewed studies comparing allozymes with other classes of nuclear DNA markers. Although both types of markers gave broadly consistent results, there was a bias favouring studies in which allozymes were more divergent than DNA markers (nine to three) and a disproportionate number of these cases involved marine taxa (seven). Furthermore, allozymes were significantly more heterogeneous than DNA markers in three of the four studies that sampled coastal and estuarine habitats. We conclude that the genetic uniformity exhibited by M. californianus may result from a combination of extensive gene flow and the lack of exposure to strong selective gradients across its range.

Selection and evaluation of housekeeping genes for haemocytes of soft-shell clams (Mya arenaria) challenged with Vibrio splendidus

Gene expression studies have opened a tremendous field of investigation in biological research over the last decades. Expression of genes is most frequently quantified by real time PCR (RT-qPCR), as this method has proven to be highly sensitive. One of the critical steps, however, in comparing transcription profiles is the availability of selected housekeeping genes. Expression of these genes should be steadily stable across the conditions under study so that they provide a baseline for gene expression comparison. Such a baseline is best established using a set of few housekeeping genes. Usually, those genes are involved in maintaining homeostasis and cell viability. In our study, nine candidate genes were used, including some commonly used housekeeping genes, such as ribosomal RNA (18S, S-15, S-18 and L-37), beta actin, ubiquitin, receptor activated C kinase (RACK) and elongation factor 1 and 2, in order to determine the most stable housekeeping genes, after haemocytes of Mya arenaria were exposed to Vibrio splendidus for 2 h. Our results showed that EF-1, S-18 and ubiquitin appear to be the most stable genes for this experimental condition. On the other hand, both 18S and beta actin, the most widely used housekeeping genes, turned out to be the least stable. This demonstrates the absolute need for preliminary assessment of housekeeping genes in gene expression studies.

Biological indices, energy reserves, steroid hormones and sexual maturity in the infaunal bivalve Scrobicularia plana from three sites differing by their level of contamination

The aim of this work was to investigate in situ biometric (condition index, hepato-somatic index, gonado-somatic index), biochemical (glycogen, lipids, sexual steroids) and histological (sex, sexual maturation stage) variables in the infaunal bivalve Scrobicularia plana. First, the reproductive cycle of S. plana was assessed by collecting bivalves from a reference site (the bay of Bourgneuf, Fr) in April, May, July, September and November 2005 and in January and March 2006. Then, S. plana were collected at three key periods of their sexual cycle (March 2006, beginning of gametogenesis; June 2006, spawning; and September 2006, spent) in three sites differing by their level of contamination (bay of Bourgneuf, reference site; Loire and Seine estuaries; Fr, impacted sites). The reproductive cycle of S. plana was well defined with a clear spawning period between May and July, sexual repose from November to January. Development of the gonad began in January and ended in September. Sex-ratio was determined during spawning and the influence of sex on biochemical variables was examined. Progesterone, 17beta-estradiol and testosterone levels in the gonad of S. plana were close to those reported in other bivalves. This study is the first to demonstrate in situ influence of site, sex and sexual maturity on energy reserves, and sexual steroids in S. plana. Even if interpretation of results is complex due to interferences between natural and anthropogenic factors, S. plana is a suitable species for estuarine studies and a better understanding of its reproduction will permit to assess impacts of environmental pollutants.