The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong SAR.
State Key Laboratory of Respiratory Disease, The Third Affiliated Hospital of Guangzhou Medical University, Guangzhou, China.
Glob Chang Biol. 2021 Aug;27(16):3779-3797. doi: 10.1111/gcb.15675. Epub 2021 May 27.
Biomineralization is one of the key processes that is notably affected in marine calcifiers such as oysters under ocean acidification (OA). Understanding molecular changes in the biomineralization process under OA and its heritability, therefore, is key to developing conservation strategies for protecting ecologically and economically important oyster species. To do this, in this study, we have explicitly chosen the tissue involved in biomineralization (mantle) of an estuarine commercial oyster species, Crassostrea hongkongensis. The primary aim of this study is to understand the influence of DNA methylation over gene expression of mantle tissue under decreased ~pH 7.4, a proxy of OA, and to extrapolate if these molecular changes can be observed in the product of biomineralization-the shell. We grew early juvenile C. hongkongensis, under decreased ~pH 7.4 and control ~pH 8.0 over 4.5 months and studied OA-induced DNA methylation and gene expression patterns along with shell properties such as microstructure, crystal orientation and hardness. The population of oysters used in this study was found to be moderately resilient to OA at the end of the experiment. The expression of key biomineralization-related genes such as carbonic anhydrase and alkaline phosphatase remained unaffected; thus, the mechanical properties of the shell (shell growth rate, hardness and crystal orientation) were also maintained without any significant difference between control and OA conditions with signs of severe dissolution. In addition, this study makes three major conclusions: (1) higher expression of Ca binding/signalling-related genes in the mantle plays a key role in maintaining biomineralization under OA; (2) DNA methylation changes occur in response to OA; however, these methylation changes do not directly control gene expression; and (3) OA would be more of a 'dissolution problem' rather than a 'biomineralization problem' for resilient species that maintain calcification rate with normal shell growth and mechanical properties.
生物矿化是海洋钙化生物（如牡蛎）在海洋酸化（OA）下受到显著影响的关键过程之一。因此，了解 OA 下生物矿化过程中的分子变化及其遗传性，是制定保护具有生态和经济重要性的牡蛎物种的保护策略的关键。为此，在这项研究中，我们明确选择了河口商业牡蛎物种香港牡蛎（Crassostrea hongkongensis）的参与生物矿化的组织（套膜）。本研究的主要目的是了解在 ~pH7.4 降低的条件下（OA 的替代物），套膜组织中的 DNA 甲基化对基因表达的影响，并推断这些分子变化是否可以在生物矿化产物-贝壳中观察到。我们在 ~pH7.4 降低和 ~pH8.0 对照条件下，经过 4.5 个月的时间，培育了早期的香港牡蛎幼虫，并研究了 OA 诱导的 DNA 甲基化和基因表达模式，以及贝壳的特性，如微观结构、晶体取向和硬度。研究结束时，发现该研究中的牡蛎种群对 OA 具有中等的弹性。关键的生物矿化相关基因（如碳酸酐酶和碱性磷酸酶）的表达不受影响；因此，贝壳的机械性能（贝壳生长速度、硬度和晶体取向）也得以维持，在对照和 OA 条件下没有显著差异，只是有严重溶解的迹象。此外，本研究得出了三个主要结论：（1）套膜中与钙结合/信号相关的基因表达较高，在 OA 下对维持生物矿化起着关键作用；（2）DNA 甲基化变化是对 OA 的响应；然而，这些甲基化变化并不直接控制基因表达；（3）OA 对具有弹性的物种来说，更像是一个“溶解问题”，而不是“生物矿化问题”，因为这些物种能够保持钙化率，同时具有正常的贝壳生长和机械性能。
