Molecular identification and expression of the phosphoglucomutase (PGM) gene from the Pacific oyster Crassostrea gigas

Bioconcentration, biotransformation, and transcriptomic impact of the UV-filter 4-MBC in the manila clam Ruditapes philippinarum

Ultraviolet filters (UV-filters) are compounds extensively used in personal care products. These compounds are produced at increasing rates and discharged into marine ecosystems in unknown quantities and with no regulation, making them emerging contaminants. Among those, the UV-filter 4-Methylbenzylidene camphor (4-MBC) is used in a variety of personal care products such as sunscreens, soaps, or lipsticks. This high consumption has resulted in its presence in various environmental matrices at in concentrations ranging from ng to μg L-1. Very little is known, however, about the possible adverse effects in exposed non-target organisms. Our study presents novel data on the bioconcentration, toxicokinetics, and molecular effects of 4-MBC in a marine bivalve species of commercial interest, Ruditapes philippinarum (Manila clam). Organisms were exposed at two different concentrations (1.34 and 10.79 μg L-1) of 4-MBC for 7 days, followed by a 3-day depuration period (clean sea waters). Bioconcentration factors (BCF) were 3562 and 2229 L kg-1 for the low and high exposure concentrations, respectively, making this pollutant bioaccumulative according to REACH criteria. Up to six 4-MBC biotransformation products (BTPs)were identified, 2 of them for the first time. Transcriptomic analysis revealed between 658 and 1310 differently expressed genes (DEGs) after 4-MBC exposure. Functional and enrichment analysis of the DEGs showed the activation of the detoxification pathway to metabolize and excrete the bioconcentrated 4-MBC, which also involved energy depletion and caused an impact on the metabolism of carbohydrates and lipids and in the oxidative phosphorylation pathways. Oxidative stress and immune response were also evidenced through the activation of cathepsins and the complement system. Such elucidation of the mode of action of a ubiquitous pollutant such as 4-MBC at the molecular level is valuable both from an environmental point of view and for the sustainable production of Manila clam, one of the most cultivated mollusk species worldwide.

Transcriptomic and metabolomic integration to assess the response of gilthead sea bream (Sparus aurata) exposed to the most used insect repellent: DEET

DEET is one of the most frequently detected insect repellents in the environment reaching concentrations of several μg L^-1 in surface water. There is scarce information available regarding its mode of action in non-target organisms. Here, we have used an integrated metabolomic and transcriptomic approach to elucidate the possible adverse effects of DEET exposure in the marine fish gilthead sea bream (Sparus aurata). Individuals were exposed at an environmentally relevant concentration of DEET (10 μg L^-1) for 22 days in a continuous flow-through system. Transcriptomic analysis revealed 250 differentially expressed genes in liver, while metabolomic analysis identified 190 differentially modulated features in liver and 98 in plasma. Multi-omic data integration and visualization allowed elucidation of the modes of action of DEET exposure, including: energy depletion through the disruption of carbohydrate and amino acids metabolisms, oxidative stress leading to DNA damage, lipid peroxidation, and damage to cell membrane and apoptosis. Activation of xenobiotic pathway as well as the inmune-inflammatory reaction was evidenced in the present work.

Balanced Polymorphism at the Pgm-1 Locus of the Pompeii Worm Alvinella pompejana and Its Variant Adaptability Is Only Governed by Two QE Mutations at Linked Sites

The polychaete Alvinella pompejana lives exclusively on the walls of deep-sea hydrothermal chimneys along the East Pacific Rise (EPR), and displays specific adaptations to withstand the high temperatures and hypoxia associated with this highly variable habitat. Previous studies have revealed the existence of a balanced polymorphism on the enzyme phosphoglucomutase associated with thermal variations, where allozymes 90 and 100 exhibit different optimal activities and thermostabilities. Exploration of the mutational landscape of phosphoglucomutase 1 revealed the maintenance of four highly divergent allelic lineages encoding the three most frequent electromorphs over the geographic range of A. pompejana. This polymorphism is only governed by two linked amino acid replacements, located in exon 3 (E155Q and E190Q). A two-niche model of selection, including ‘cold’ and ‘hot’ conditions, represents the most likely scenario for the long-term persistence of these isoforms. Using directed mutagenesis and the expression of the three recombinant variants allowed us to test the additive effect of these two mutations on the biochemical properties of this enzyme. Our results are coherent with those previously obtained from native proteins, and reveal a thermodynamic trade-off between protein thermostability and catalysis, which is likely to have maintained these functional phenotypes prior to the geographic separation of populations across the Equator about 1.2 million years ago.

Association and Functional Analyses Revealed That PPP1R3B Plays an Important Role in the Regulation of Glycogen Content in the Pacific Oyster Crassostrea gigas

The Pacific oyster (Crassostrea gigas) is one of the most important aquaculture species worldwide. Glycogen contributes greatly to the special taste and creamy white color of oysters. Previous genome-wide association studies (GWAS) identified several single nucleotide polymorphism (SNP) sites that were strongly related to glycogen content. Genes within 100 kb upstream and downstream of the associated SNPs were screened. One gene annotated as protein phosphatase 1 regulatory subunit 3B (PPP1R3B), which can promote glycogen synthesis together with protein phosphatase 1 catalytic subunit (PPP1C) in mammals, was selected as a candidate gene in this study. First, full-length CgPPP1R3B was cloned and its function was characterized. The gene expression profiles of CgPPP1R3B in different tissues and seasons showed a close relationship to glycogen content. RNA interference (RNAi) experiments of this gene in vivo showed that decreased CgPPP1R3B levels resulted in lower glycogen contents in the experimental group than in the control group. Co-immunoprecipitation (Co-IP) and yeast two-hybrid (Y2H) assays indicated that CgPPP1R3B can interact with CgPPP1C, glycogen synthase (CgGS) and glycogen phosphorylase (CgGP), thus participating in glycogen metabolism. Co-sedimentation analysis in vitro demonstrated that the CgPPP1R3B protein can bind to glycogen molecules directly, and these results indicated the conserved function of the CgPPP1R3B protein compared to that of mammals. In addition, thirteen SNPs were precisely mapped in this gene. Ten of the thirteen SNPs were confirmed to be significantly (p < 0.05) related to glycogen content in an independent wild population (n = 288). The CgPPP1R3B levels in oysters with high glycogen content were significantly higher than those of oysters with low glycogen content, and gene expression levels were significantly associated with various genotypes of four associated SNPs (p < 0.05). The data indicated that the associated SNPs may control glycogen content by regulating CgPPP1R3B expression. These results suggest that CgPPP1R3B is an important gene for glycogen metabolic regulation and that the associated SNPs of this gene are potential markers for oyster molecular breeding for increased glycogen content.

Seasonal monitoring of blue mussel (Mytilus spp.) populations in a harbor area: A focus on responses to environmental factors and chronic contamination

Coastal waters corresponding to macrotidal systems are among the most variable marine biotopes. Sessile animals as bivalve mollusks may however be found forming intertidal beds at high densities, as allowed by full adaptation to local conditions. A better knowledge of adaptive responses to environmental factors is required to foresee possible adverse effects of global change. At the sub-cellular level, transcriptional responses are among the earliest signals of environmental disturbances and they can reveal subtle and meaningful changes in organism exposed to stress. Three blue mussel (Mytilus spp.) populations inhabiting the Bay of Brest (France) in sites exposed to different levels of chronic pollution, from low to moderate, were surveyed upon a seasonal schedule, with special attention to the reproductive cycle. Major seawater parameters were monitored over a full-year in the framework of the S!RANO project, based on an automatic high frequency acquisition system installed aboard a ship of opportunity. The health status of mussels has been assessed by measuring a condition index and gametogenesis has been followed by histology. Selected biological responses to environmental stress were detected using a multimarker approach including expression of genes involved in chemical stress response and energetic metabolism, and cellular immune parameters. Environmental parameters showed deep seasonal variations which differed among sites. Most biological responses followed a seasonal pattern. Late winter and spring corresponded to an active reproduction period in the Bay of Brest. Earlier spawning was observed in harbor areas compared to the oceanic site and an altered physiological state was assumed in commercial harbor mussels during the reproductive period, suggesting that their health is compromised at this time of year. However, no signs of severe chemical stress were detected in both harbor mussel populations, which could reflect adaptive responses to adverse environmental conditions.

Identification of cadmium-induced Agaricus blazei genes through suppression subtractive hybridization

Cadmium (Cd) is one of the most serious environmental pollutants. Filamentous fungi are very promising organisms for controlling and reducing the amount of heavy metals released by human and industrial activities. However, the molecular mechanisms involved in Cd accumulation and tolerance of filamentous fungi are not fully understood. Agaricus blazei Murrill, an edible mushroom with medicinal properties, demonstrates high tolerance for heavy metals, especially Cd. To investigate the molecular mechanisms underlying the response of A. blazei after Cd exposure, we constructed a forward subtractive library that represents cadmium-induced genes in A. blazei under 4 ppm Cd stress for 14 days using suppression subtractive hybridization combined with mirror orientation selection. Differential screening allowed us to identify 39 upregulated genes, 26 of which are involved in metabolism, protein fate, cellular transport, transport facilitation and transport routes, cell rescue, defense and virulence, transcription, and the action of proteins with a binding function, and 13 are encoding hypothetical proteins with unknown functions. Induction of six A. blazei genes after Cd exposure was further confirmed by RT-qPCR. The cDNAs isolated in this study contribute to our understanding of genes involved in the biochemical pathways that participate in the response of filamentous fungi to Cd exposure.

Responses of Pacific oyster Crassostrea gigas populations to abiotic stress in environmentally contrasted estuaries along the Atlantic coast of France

Genetic and ecophysiological responses of oyster, Crassostrea gigas, populations to environmental stress were investigated in three highly contaminated French estuaries (the Gironde, Loire and Vilaine) and compared to a control, the Belon estuary. A strong response in both metallothionein CgMT4 mRNA expression, as determined by semi-quantitative RT-PCR, and amount of protein, as determined by ELISA tests, was demonstrated in estuarine populations subjected to differential contamination, with an inhibition in the area most highly contaminated with metals. In these same estuarine populations, we found polymorphisms of the metallothionein CgMT4 gene and three other genes (glutamine synthetase--GS, delta-9 desaturase--D9 and phosphoglucomutase--PGM) involved in stress response of C. gigas. We showed that genetic differentiation was observed for MT4 and PGM genes in the Gironde estuary which is highly contaminated with metals. A strong seasonal effect was observed. Phenotype-genotype coupling revealed that one particular MT4 allele and one PGM allele seemed to be associated with metal sensitivity expressed as lower detoxification efficiency and higher metal bioaccumulation. The MT4 gene is a good physiological and genetic marker of stress response and susceptibility.

Genotype-dependent recovery from acute exposure to heavy metal contamination in the freshwater clam Sphaerium novaezelandiae

The ability to recover from environmental perturbations is essential for the sustainability of ecological systems. Variation in the ability of individual organisms to recover from stressors influences overall resilience at higher levels of biological organisation. Such variation is likely to be genetically based. To investigate this hypothesis we examined the genetic basis of both resistance to and recovery from zinc, a common stormwater contaminant, in the New Zealand freshwater clam Sphaerium novaezelandiae. We undertook a 4-day toxicity test using zinc exposure concentrations ranging from 0.31 to 5.00 mg/L. These concentrations are consistent with levels recorded in urban streams during the first flush of storms. As our response measures we recorded mortality at the end of the 4-day period, as well as reburial rate (time to rebury in sediment) following the 4-day exposure ("exposure") and then again following a 24h period of recovery ("recovery"). Genotypic composition was determined using allozyme electrophoresis, focusing on the enzyme Pgm (phosphoglucomutase). Overall, a significant effect on mortality was observed, with an average value of 78.6% (+/-7.9) at 5.00 mg/L zinc, compared with only 3.8% (+/-3.8) mortality at 0.31 mg/L zinc. An inhibition concentration (IC(50)) of 1.16 mg/L was recorded, when considered regardless of genotypes. There was no significant genotype-specific differences in mortality. There was a significant difference in reburial rates across all genotypes at the end of the exposure period with an average reburial time of 83.0+/-3.6 min at 5.00 mg/L (22.8+/-2.9 min at 0.31 mg/L). There was a near-significant (p=0.058) difference in time taken to rebury when comparing between genotypes at the "exposure" stage for any concentration. Significant differences in reburial rates across all genotypes were also observed following 24h recovery. When individual genotypes were compared at this stage, genotype 33 reburied on average significantly faster (24.0+/-4.5 min) than other genotypes at the highest exposure concentration and was also significantly faster than genotype 44 at 1.25mg/L. Studies investigating the genetic basis to recovery from stressors at an individual level are limited. This study has shown that populations of organisms display genetically-based variation in their ability to recover from zinc exposure in the laboratory and that such variation is linked to a physiological trait (reburial). The potential effects on other life history traits (e.g. feeding), possible physiological trade-offs and the implications for such variation on ecosystem resilience requires further investigation.