柯才焕教授课题组近日在Scientific Reports期刊发表题为“Transcriptome analysis of the key role of GAT2 gene in the hyper-accumulation of copper in the oyster Crassostrea angulata”研究论文，研究了影响牡蛎铜累积的关键基因，并阐述了牡蛎铜富集个体差异的形成机制。
牡蛎对铜、锌等金属具有非常强的富集能力，经常被用于指示河口污染情况。随着工业发展，近岸河口区遭受越来越严重的铜污染。因此牡蛎对铜的超富集现象越来越被人们所关注。牡蛎对铜富集存在非常大的个体差异，然而相关的研究却非常有限，特别是缺少分子机制的解析。
本研究以福建牡蛎(Crassostrea angulata)作为研究对象，选取了两组存在铜富集差异（3-4倍）福建牡蛎的组织进行基因转录水平分析。通过对差异基因的分析，建立了如下科学假设：牡蛎神经递质转运体基因的差异表达(GAT2基因)，可以影响牡蛎神经系统调控的生理行为，从而改变铜的富集动力学过程，产生铜富集个体差异现象；铜离子结合、转运相关的基因 (ABCB家族、Laccase家族、载脂蛋白基因) 表达量显著上调，则使铜富集量高的牡蛎个体能够保证细胞内铜稳态，免受铜的毒害（图1所示）。
图1. 牡蛎中与铜富集个体差异相关的重要功能基因示意图
Fig. 1 The sketch map of important functional genes related to the inter-individual variations of Cu in oysters.
为了验证这个设想，选取神经递质转运体GAT2基因进一步研究。发现在该基因沉默后，牡蛎鳃和外套膜中铜富集量显著降低，而在GABA受体拮抗剂注射后牡蛎铜富集量显著升高。GAT2基因的表达差异可能是引起牡蛎铜富集个体差异的关键因素，GAT2转运体可以通过调节牡蛎体内GABA对神经系统的刺激来控制牡蛎的行为，像滤水、排泄等活动，而这些行为都会影响铜吸收或者外排的动力学过程。
本研究首次发现神经递质转运体在贝类金属累积中起到重要作用，丰富了海洋双壳类金属富集的分子机制。对牡蛎铜富集个体差异的解析，也为进一步培育铜富集量低的牡蛎品系提供理论基础。
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
