Gene expression correlated with delay in shell formation in larval Pacific oysters (Crassostrea gigas) exposed to experimental ocean acidification provides insights into shell formation mechanisms

Authors: DE WIT, PIERRE - University Of Gothenburg; DURLAND, EVAN - Oregon State University; VENTURA, ALEXANDER - University Of Gothenburg; LANGDON, CHRIS - Oregon State University

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2018
Publication Date: 2/22/2018
Citation: De Wit, P., Durland, E., Ventura, A., Langdon, C.J. 2018. Gene expression correlated with delay in shell formation in larval Pacific oysters (Crassostrea gigas) exposed to experimental ocean acidification provides insights into shell formation mechanisms. BMC Genomics. 19:160. https://doi.org/10.1186/s12864-018-4519-y.
DOI: https://doi.org/10.1186/s12864-018-4519-y

Interpretive Summary: Recent work has been conducted to characterize gene expression changes that are associated with larval development in oysters, but the mechanism by which larval oysters first form their shell is still largely unknown. In Pacific oysters (Crassostrea gigas), this shell forms within the first 24 hours after eggs are fertilized, and it has been demonstrated that changes in water chemistry like reduced concentrations of aragonite, the key component of their shell, can cause delays in shell formation, shell deformations and higher mortality rates. In this study, the delay in shell formation associated with exposure to CO2-acidified seawater was used to identify genes correlated with initial shell deposition. By fitting linear models to gene expression data for oyster larvae exposed to ambient and low aragonite saturation treatments, 37 annotated genes were isolated and correlated with initial larval shell formation. The genes were categorized into ion transporters, shell matrix proteins and protease inhibitors and gene expression data also implied an important role of dynein motor proteins as transporters of cellular components during the initial shell formation process. This use of an RNA-Seq approach with high temporal resolution allowed a conceptual model for how oyster larval calcification is initiated to be constructed. Results provide a foundation for further studies on how genetic variation in these identified genes could affect fitness of oyster populations subjected to future environmental changes, such as ocean acidification.

Technical Abstract: Despite recent work to characterize gene expression changes associated with larval development in oysters, the mechanism by which the larval shell is first formed is still largely unknown. In Crassostrea gigas, this shell forms within the first 24 hours post fertilization, and it has been demonstrated that changes in water chemistry can cause delays in shell formation, shell deformations and higher mortality rates. In this study, we use the delay in shell formation associated with exposure to CO2-acidified seawater to identify genes correlated with initial shell deposition. By fitting linear models to gene expression data in ambient and low aragonite saturation treatments, we are able to isolate 37 annotated genes correlated with initial larval shell formation, which can be categorized into 1) ion transporters, 2) shell matrix proteins and 3)protease inhibitors. Clustering of the gene expression data into co-expression networks further supports the result of the linear models, and also implies an important role of dynein motor proteins as transporters of cellular components during the initial shell formation process. Using an RNA-Seq approach with high temporal resolution allows us to identify a conceptual model for how oyster larval calcification is initiated. This work provides a foundation for further studies on how genetic variation in these identified genes could affect fitness of oyster populations subjected to future environmental changes, such as ocean acidification.