萨罗罗非鱼NKCC1α基因cDNA克隆及mRNA组织表达差异
cDNA cloning and tissue-differential expression of Na+/K+/2Cl- −cotransporter 1-α isoform in Sarotherodon melanotheron
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摘要: 在鱼类适应盐度变化的过程中, 鱼鳃是进行渗透调节的主要器官, NKCC1α基因是保持鳃丝氯细胞渗透平衡的关键离子转运器, 以1Na+:1 K+ :2Cl –的比例进行电中性转运。萨罗罗非鱼(Sarotherodon melanothern)是耐盐强的广盐性鱼类之一。该文通过快速扩增cDNA末端的方法, 首次从萨罗罗非鱼鳃丝组织中分离出NKCC1α 基因cDNA 全长序列, 其开放阅读框(ORF)包含1 151个氨基酸残基。多重比对和聚类分析结果表明, 该试验获得的基因序列与莫桑比克罗非鱼、鲑及鳗鲡的NKCC1α最为相似, 其中萨罗罗非鱼与莫桑比克罗非鱼相似性最高(99%)。预测萨罗罗非鱼NKCC1α蛋白质二级结构包含10个跨膜螺旋, 这些跨膜螺旋的氨基酸序列及其布局都非常保守; 应用实时荧光定量PCR(qRT-PCR)检测鳃、肝、肠、肾NKCC1α mRNA相对含量, 这4种组织间差异显著; 盐度显著影响NKCC1α在鳃组织中的表达, 在136盐度下NKCC1α mRNA相对表达水平为0盐度下的4.9倍, 差异极显著(P<0.001), 显示NKCC1α基因与萨罗罗非鱼的耐盐性能密切相关。Abstract: The gills are the major apparatus for osmoregulation in fish to acclimate the changes of salinities. Na+/K+/2Cl−cotransporter 1-α (NKCC1α) is one of the key ion cotransporter locoalized in gill chloride cells which has been associated with the maintence of osmotic homeostasis. The transport process mediated by NKCC1α is characterized by electroneutrality with a stoichiometry of 1Na:1K:2Cl. Sarotherodon melanotheron is one of the most euryhaline teleosts able to withstand variations in environmental salinity ranging from freshwater to hyper-saline waters. In this study, the reverse transcription-polymerase chain reaction and rapid amplification of 3' and 5'cDNA ends methods were used to identify the full cDNA of the NKCC1α with an Open Reading Frame which contains 1 151aa of S.melanotheron. The amino acid multiple alignment and phylogenetic analysis showed that this isoform is more similar with isoforms in Oreochromis mossambicus, Salmo salar and Anguilla anguilla, and there is the highest homologous of 99% between Sarotherodon and Mossambique. The predicted protein secondly structure of NKCC1α contains 10 transmenbrane domains, which were highly conserved in sequences and locoalization sites relatively to other species. The quantitative real time polymerase chain reaction (qRT-PCR) assay was developed to estimate the mRNA expression levels in gill, liver, intestine and kidney in freshwater, the results showed a tissue-specific model. Furthermore, the sanility significantly affects the relative expression level of NKCC1α mRNA in gill with a 4.9 times higher in 136 salinity water than that in 0 salinity. The results suggest that the NKCC1α is closely related to the salt tolerance in S.melanotheron.