Project description:Endogenously determined inter-individual differences in growth rate of bivalve molluscs have been widely analyzed at different organizational levels. Most studies have focused on the characterization of the physiological differences between fast (F) and slow (S) growing individuals. Although several genes have been described to be up regulated on fast growing individuals, the molecular basis underlying the mechanisms at the origin of growth variation is still poorly understood. In the present study we reared mussel spat of the species Mytilus galloprovincialis under diets below the pseudofaeces threshold (BP) and above the pseudofaeces threshold (AP). After 3 months, F and S mussels on each condition were selected, so that 4 experimental groups were obtained: FBP, SBP, FAP and SAP. We hypothesized that nurturing conditions during their growing period would modify the molecular basis of growth rate differences. However, results of feeding experiments showed that F mussels displayed higher clearance and ingestion rates and higher efficiencies of food selection prior to ingestion, as well as higher gill surface areas, irrespective of the rearing nutritional environment. To decipher molecular mechanism at the origin of growth variation, gills of the 4 mussel groups were dissected, and used for transcriptome analysis with a custom Agilent single channel microarray. Gene expression analysis revealed i) a low number (12) of genes differentially expressed associated to maintenance condition differences and ii) 117 genes differentially expressed when comparing fast and slow growing mussels (FBP + FAP vs. SBP + SAP). We further investigated this comparison: GO terms and KEGG pathway association of the differentially expressed genes allowed us to analyze the functions involved on the differentially expressed encoding. Transcriptomic differences between F and S mussels were mainly based on the up-regulation of response to stimulus, growth and cell activity Biological Process GO terms. Regarding the KEGG terms, carbohydrate metabolism and Krebs cycle were found to be up-regulated in F mussels whereas biosynthetic processes were up-regulated in S mussels. Among the differentially expressed genes that are annotated, the following ones were found to be up regulated in F mussels: i) Mucin, related to mucus secretion, known to be crucial in food acquisition and pre-ingestive selection processes in bivalves, ii) genes related to growth such as Myostatin or Insulin-like growth factor, iii) genes involved in feeding activity, such as Fibrocystin or Dynein and iv) genes involved in the energetic metabolism; Citrate synthase. S mussels mainly over-expressed genes related to immune system and defence (Leucine-rich repeat-containing protein, Metalloendopeptidase, Small heat shock protein 24, Multidrug resistance,…).The present results suggest that differences in feeding activity and in the allocation of metabolic energy between growth groups could account for the differences in growth rate in spat of Mytilus galloprovincialis. In accordance with their higher feeding rates and growth, fast growing mussels were found to mainly over-express genes involved in the development and maintenance of such activities, however, slow growing mussels needed to expend energy in immune and defence processes to ensure survival at the expense of growth rate.

Project description:Transcriptional profiling of natural population of mussels (Mytilus galloprovincialis) -digestive gland tissue- comparing female individuals sampled in the Bizerta Lagoon, Tunisia, across May 2007 - April 2008. Background: Seasonal environmental changes may affect the physiology of Mytilus galloprovincialis (Lam.), an intertidal filter-feeder bivalve occurring commonly in Mediterranean and Atlantic coastal areas. We investigated seasonal variations in relative transcript abundance of the digestive gland and the mantle (gonads) of males and females. To identify gene expression trends, we used a medium-density cDNA microarray (1.7 K probes) in dual-color competitive hybridization analyses. Results: Hierarchical clustering of digestive gland microarray data showed two main branches, distinguishing profiles associated with the M-bM-^@M-^\hotM-bM-^@M-^] months (MayM-bM-^@M-^SAugust) from the other months. Genes involved in chitin metabolism, associated with mussel nutrition and digestion, showed higher expression during summer. Moreover, we found different gene expression patterns in the digestive glands of males and females during the four stages of mussel gonadal development. Microarray data from gonadal transcripts also displayed clear patterns during the different developmental phases with peak relative mRNA abundance at the ripe phase (stage III) for both sexes. Conclusion: These data showed a clear temporal pattern in gene expression profiles of mussels sampled over an annual cycle. Physiological response to thermal variation, food availability, and reproductive status across months may contribute to variation in gene expression. Loop design: Female individuals from 12 different months across one year (May 2007 to April 2008). Dual color competitive hybridizations (month n vs month n+1) including dye swap. Single individuals. Three (May 2007 to December 2007) or four biological replicates (January 2008 to April 2008 ). One replicate per array.

Project description:Transcriptional profiling of mussel (Mytilus galloprovincialis) digestive gland tissue comparing control tissue with tissue obtained from animals exposed to sublethal amounts of Chlorpyrifos, animals injected into the posterior adductor muscle with 25 pico-moles 17β-estradiol (E2) and animals pre-exposed for three days to the pesticide and further injected with E2. Background: Many pesticides have been shown to act as endocrine disrupters. Although the potencies of currently used pesticides as hormone agonists/antagonists in vitro are low compared with those of natural ligands, their ability to act via multiple mechanisms might enhance the biological effect. The organophosphate Chlorpyrifos (CHP) has been shown to be weakly estrogenic and cause adverse neurodevelopmental effects in mammals. However, no information is available on the possible endocrine effects of CHP in aquatic organisms. In the digestive gland of the bivalve Mytilus galloprovincialis, a target tissue for the action of both estrogens and pesticides, the possible effects of CHP on the responses to the natural estrogen 17β-estradiol (E2) were investigated. Methodology/Principal findings: Mussels were exposed to CHP (4.5 mg/l, 72 hrs) and subsequently injected with E2 (6.75 ng/g dw). Responses were evaluated in CHP, E2 and CHP/E2 treatment groups at 24 h p.i. by a biomarker/transcriptomic approach. CHP and E2 induced additive, synergistic, and antagonistic effects on lysosomal biomarkers (lysosomal membrane stability, lysosome/cytoplasm volume ratio, lipofuscin and neutral lipid accumulation). Additive and synergistic effects were also observed on the expression of estrogen-responsive genes (GSTπ, catalase and 5-HTR) evaluated by RT-Q-PCR. The use of a 1.7K cDNA Mytilus microarray showed that CHP, E2 and CHP/E2, induced 81, 44, and 65 Differentially Expressed Genes (DEGs), respectively. 24 genes were exclusively shared between CHP and CHP/E2, only 2 genes between E2 and CHP/E2. Moreover, 36 genes were uniquely modulated by CHP/E2. Gene ontology annotation was used to elucidate the putative mechanisms involved in the responses elicited by different treatments. Conclusions: The results show complex interactions between CHP and E2 in mussel digestive gland, indicating that the combination of certain pesticides and hormones may give rise to unexpected effects at the molecular/cellular level. Overall, these data demonstrate that CHP can interfere with the mussel responses to natural estrogens.

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Molecular basis of fast and slow growing individuals of the mussel Mytilus galloprovincialis

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