Fan Weimin, Li Changzhong, Wang Xue, Gong Ningping, Xie Liping, Zhang Rongqing
Institute of Marine Biotechnology, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China.
J Biosci Bioeng. 2007 Jul;104(1):47-54. doi: 10.1263/jbb.104.47.
The absorption, transport and localization of calcium underlie the basis of biomineralization, and Ca(2+) entry into epithelial cell is the primary step in shell formation. However, the related mechanism of Ca(2+) transport is poorly documented at the gene or protein level. L-type voltage-dependent calcium channels may be involved in calcium transport for biomineralization in some marine invertebrates. In this study, a full-length cDNA of a voltage-dependent calcium channel beta subunit from Pinctada fucata (PCabeta) was cloned, and its amino acid sequence was deduced. PCabeta shared 51%-67% apparently sequence identity with voltage-dependent calcium channel beta subunits from other species. However, PCabeta was much shorter than other voltage-dependent calcium channel beta subunits particularly at the carboxyl terminus, indicating that it is likely a truncated beta subunit isoform. Semi-quantitative RT-PCR analysis showed that PCabeta was expressed in all the tested tissues and that it had a higher expression level in the gill tissue and hemolymph than in other tissues, suggesting that L-type voltage-dependent calcium channels are responsible for Ca(2+) absorption in the gill and Ca(2+) entry into hemocytes. In the mantle, PCabeta mRNA was predominantly expressed in the inner and middle folds of the mantle epithelium, suggesting that L-type voltage-dependent calcium channels are involved in Ca(2+) absorption from the ambient medium in the mantle. All these results suggest that voltage-dependent calcium channels are involved in Ca(2+) uptake and transport during oyster biomineralization.
钙的吸收、转运和定位是生物矿化的基础，而Ca(2+)进入上皮细胞是贝壳形成的首要步骤。然而，在基因或蛋白质水平上，Ca(2+)转运的相关机制鲜有文献记载。L型电压依赖性钙通道可能参与了一些海洋无脊椎动物生物矿化过程中的钙转运。在本研究中，克隆了合浦珠母贝电压依赖性钙通道β亚基的全长cDNA（PCabeta），并推导了其氨基酸序列。PCabeta与其他物种的电压依赖性钙通道β亚基的序列一致性明显为51%-67%。然而，PCabeta比其他电压依赖性钙通道β亚基短得多，尤其是在羧基末端，这表明它可能是一个截短的β亚基异构体。半定量RT-PCR分析表明，PCabeta在所有测试组织中均有表达，且在鳃组织和血淋巴中的表达水平高于其他组织，这表明L型电压依赖性钙通道负责鳃中的Ca(2+)吸收以及Ca(2+)进入血细胞。在贝壳中，PCabeta mRNA主要在贝壳上皮的内褶和中褶中表达，这表明L型电压依赖性钙通道参与了贝壳中从周围介质吸收Ca(2+)的过程。所有这些结果表明，电压依赖性钙通道参与了牡蛎生物矿化过程中的Ca(2+)摄取和转运。
