Recently the group of Professor Caihuan Ke has published the paper “Transcriptome analysis of the key role of GAT2 gene in the hyper-accumulation of copper in the oyster Crassostrea angulate”in Scientific Reports. This paper attempts to explain the molecular mechanisms of the intra-species differences in Cu body concentrations in oyster Crassostrea angulata and to identify the key genes related to Cu accumulation.

Oysters are considered as the hyper-accumulators of various metals, especially for Cu, zinc (Zn), and cadmium (Cd), which have been extensively employed in metal contamination monitoring. Due to human activities, an increasing amount of industrial sewage is released into rivers and coastal waters, and high levels of Cu have been reported in some aquatic ecosystem. One paradigm of oysters as the hyper-accumulators of Cu is the inter-individual variations, but the molecular mechanisms remain very elusive.

In this study, a comprehensive analysis of the transcriptome of Crassostrea angulata was conducted to reveal the relationship between gene expression and differential Cu body burdens (3-4 fold) in oysters. Scientific hypotheses are put forward after analysing for the differentially expressed genes: the neurotransmitter transporter (GAT2) might affect the oyster behavior, which in turn led to differences in Cu accumulation；the expression levels of genes related to Cu binding and transport (ABCBs, Laccases, apolipophorin) were significantly up-regulated，which played an important role in the maintenance of cell Cu homeostasis（Fig.1）。

Fig. 1 The sketch map of important functional genes related to the inter-individual variations of Cu in oysters.

In order to prove the scientific hypothesis, we further studied the roles of GAT2 in mediating Cu accumulation. GAT2-silenced oysters showed a significant reduction in Cu concentration in both the gills and mantles. Gill Cu concentrations increased significantly after GABA receptor antagonists treatments. This finding suggested that the differences in GAT2 transcriptional expression could lead to changes in Cu concentrations. When the GAT2 gene was upregulated in some individuals, inhibitory and excitatory actions in the central neurons were elicited by GABA suppressed. We therefore inferred that neurotransmitters, especially GABA, which was regulated by GAT2, can change the oyster behavior, which may have an impact on the biodynamics of Cu. It is the first report that neurotransmitters can affect the metal accumulation in molluscs.

Abstract：

One paradigm of oysters as the hyper-accumulators of many toxic metals is the inter-individual variation of metals, but the molecular mechanisms remain very elusive. A comprehensive analysis of the transcriptome of Crassostreaangulata was conducted to reveal the relationship between gene expression and differential Cu body burden in oysters. Gene ontology analysis for the differentially expressed genes showed that the neurotransmitter transporter might affect the oyster behavior, which in turn led to difference in Cu accumulation. The ATP-binding cassette transporters superfamily played an important role in the maintenance of cell Cu homeostasis, vitellogenin and apolipophorin transport, and elimination of excess Cu. Gill and mantle Cu concentrations were significantly reduced after silencing the GABA transporter 2 (GAT2) gene, but increased after the injection of GABA receptor antagonists, suggesting that the function of GABA transporter 2 gene was strongly related to Cu accumulation. These findings demonstrated that GABA transporter can control the action of transmitter GABA in the nervous system, thereby affecting the Cu accumulation in the gills and mantles.

Citation: Bo Shi, Zekun Huang, Xu Xiang, Miaoqin Huang, Wen-Xiong Wang, and Caihuan Ke^*. Transcriptome analysis of the key role of GAT2 gene in the hyper-accumulation of copper in the oyster Crassostrea angulata. Scientific Reports. Doi: 10.1038/srep17751

Link to full text:  http://www.nature.com/articles/srep17751