Beschreibung: Marine organisms have to cope with increasing CO2 partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pCO2 treatments (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm) on mantle gene expression patterns in the blue mussel Mytilus edulis from the Baltic Sea. Based on the M. edulis mantle tissue transcriptome, the expression of several genes involved in metabolism, calcification and stress responses was assessed in the outer (marginal and pallial zone) and the inner mantle tissues (central zone) using quantitative real-time PCR. The expression of genes involved in energy and protein metabolism (F-ATPase, hexokinase and elongation factor alpha) was strongly affected by acclimation to moderately elevated CO2 partial pressures. Expression of a chitinase, potentially important for the calcification process, was strongly depressed (maximum ninefold), correlating with a linear decrease in shell growth observed in the experimental animals. Interestingly, shell matrix protein candidate genes were less affected by CO2 in both tissues. A compensatory process toward enhanced shell protection is indicated by a massive increase in the expression of tyrosinase, a gene involved in periostracum formation (maximum 220-fold). Using correlation matrices and a force-directed layout network graph, we were able to uncover possible underlying regulatory networks and the connections between different pathways, thereby providing a molecular basis of observed changes in animal physiology in response to ocean acidification.

Beschreibung: Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pallial mantle could be induced in central mantle tissue underlying the damaged shell areas. This experimental approach makes it possible to identify gene products that control the chemical micro-environment during calcification as well as organic matrix components. This is unlike existing methodological approaches that work retroactively to characterize calcification relevant molecules and are just able to examine organic matrix components that are present in completed shells. In our assay an orthogonal array of nine 1 mm holes was drilled into the left valve, and mussels were suspended in net cages for 20, 29 and 36 days to regenerate. Structural observations using stereo-microscopy, SEM and Raman spectroscopy revealed organic sheet synthesis (day 20) as the first step of shell-repair followed by the deposition of calcite crystals (days 20 and 29) and aragonite tablets (day 36). The regeneration period was characterized by time-dependent shifts in gene expression in left central mantle tissue underlying the injured shell, (i) increased expression of two tyrosinase isoforms (TYR3: 29-fold and TYR6: 5-fold) at day 20 with a decline thereafter, (ii) an increase in expression of a gene encoding a nacrein-like protein (max. 100-fold) on day 29. The expression of an acidic Asp-Ser-rich protein was enhanced during the entire regeneration process. This proof-of-principle study demonstrates that genes that are specifically expressed in pallial and marginal mantle tissue can be induced (4 out of 10 genes) in central mantle following experimental injury of the overlying shell. Our findings suggest that regeneration assays can be used systematically to better characterize gene products that are essential for distinct phases of the shell formation process, particularly those that are not incorporated into the organic shell matrix.

Beschreibung: Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pallial mantle could be induced in central mantle tissue underlying the damaged shell areas. This experimental approach makes it possible to identify gene products that control the chemical micro-environment during calcification as well as organic matrix components. This is unlike existing methodological approaches that work retroactively to characterize calcification relevant molecules and are just able to examine organic matrix components that are present in completed shells. In our assay an orthogonal array of nine 1 mm holes was drilled into the left valve, and mussels were suspended in net cages for 20, 29 and 36 days to regenerate. Structural observations using stereo-microscopy, SEM and Raman spectroscopy revealed organic sheet synthesis (day 20) as the first step of shell-repair followed by the deposition of calcite crystals (days 20 and 29) and aragonite tablets (day 36). The regeneration period was characterized by time-dependent shifts in gene expression in left central mantle tissue underlying the injured shell, (i) increased expression of two tyrosinase isoforms (TYR3: 29-fold and TYR6: 5-fold) at day 20 with a decline thereafter, (ii) an increase in expression of a gene encoding a nacrein-like protein (max. 100-fold) on day 29. The expression of an acidic Asp-Ser-rich protein was enhanced during the entire regeneration process. This proof-of-principle study demonstrates that genes that are specifically expressed in pallial and marginal mantle tissue can be induced (4 out of 10 genes) in central mantle following experimental injury of the overlying shell. Our findings suggest that regeneration assays can be used systematically to better characterize gene products that are essential for distinct phases of the shell formation process, particularly those that are not incorporated into the organic shell matrix.

Beschreibung: Marine organisms have to cope with increasing CO2 partial pressures and decreasing pH in the oceans. We elucidated the impacts of an 8-week acclimation period to four seawater pCO2 treatments (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm) on mantle gene expression patterns in the blue mussel Mytilus edulis from the Baltic Sea. Based on the M. edulis mantle tissue transcriptome, the expression of several genes involved in metabolism, calcification and stress responses was assessed in the outer (marginal and pallial zone) and the inner mantle tissues (central zone) using quantitative real-time PCR. The expression of genes involved in energy and protein metabolism (F-ATPase, hexokinase and elongation factor alpha) was strongly affected by acclimation to moderately elevated CO2 partial pressures. Expression of a chitinase, potentially important for the calcification process, was strongly depressed (maximum ninefold), correlating with a linear decrease in shell growth observed in the experimental animals. Interestingly, shell matrix protein candidate genes were less affected by CO2 in both tissues. A compensatory process toward enhanced shell protection is indicated by a massive increase in the expression of tyrosinase, a gene involved in periostracum formation (maximum 220-fold). Using correlation matrices and a force-directed layout network graph, we were able to uncover possible underlying regulatory networks and the connections between different pathways, thereby providing a molecular basis of observed changes in animal physiology in response to ocean acidification.