中文摘要：

C型凝集素是一类Ca^2＋依赖活性的糖蛋白，在虾蟹类的免疫防御中发挥着重要作用。采用RT-PCR及RACE技术首次克隆了秀丽白虾C型凝集素家族4个基因（EmCTL-1、EmCTL-2、EmCTL-3、EmCTL-4）的cDNA全长。这4个C型凝集素基因的cDNA全长分别为1390、1119、1364和1299bp，分别含996、969、1026和1044bp的开放阅读框，各编码332、322、341和347个氨基酸的蛋白。其氨基酸序列与罗氏沼虾相应的C型凝集素的相似性分别为40％、37％、69％和73％，与其他海水虾类的相似性在30％～41％之间。阳性选择模型分析显示虾类的c型凝集素基因在进化过程中经历了阳性选择。进化树分析表明，秀丽白虾的c型凝集素基因与罗氏沼虾的亲缘关系最近，并且除EmCTL-4属于十足类C型凝集素亚群A外，其他均属于亚群C。组织表达分析表明，EmCTL-1主要在血液中表达，EmCTL-2主要在性腺、血液和胸神经节中表达，而EmCTL-3和EmCTL-4则主要在精巢中表达。研究表明，秀丽白虾的C型凝集素基因具有较快的进化特点，同时又具备凝集素行使免疫功能时必需的保守氨基酸残基及钙离子结合位点，精巢和血液是秀丽白虾C型凝集素基因主要的表达器官。

英文摘要：

Exopalaemon modestus is one of the main shrimps which has high economic value. But its genetic information and functional gene background are rarely known so far. In this study, the cDNAs of four novel C- type lectins（designated as EmCTL-1 ,EmCTL-2, EmCTL-3 and EmCTL-4）were cloned from the ovary of white shrimp,E, modestus,by means of PCR and 5＇ and 3＇ rapid amplification of cDNA ends （RACE）. The full-length cDNAs consist of 1 390,1 119,1 364 and 1 299 bp with one open reading frame consisting of 996,969,1 026 and 1 044 bp,encoding 332,322,341 and 347 amino acids respectively. Their deduced amino acid sequences contained a putative signal peptide of 19,21,20 and 17 amino acid residues respectively. The four C-type lectin genes all contained two carbohydrate recognition domains,CRD1 and CRD2. The CRD1 was composed of 128 residues in EmCTL-2 and EmCTL-3,127 residues in EmCTL-i and 126 residues in EmCTL-4. And the CRD2 was composed of 127 residues in EmCTL-1 and EmCTL-3,129 residues in EmCTL-2 and 130 residues in EmCTL-4. Both the CRD1 and CRD2 had 6 conserved cysteine residues and 3 conserved tryptophane residues. The motif of Ca^2＋ binding sites 2 were EPA and FND in EmCTL-1 ,EPA and FHD in EmCTL-2,WHD and FDD in EmCTL-3 and EPD and FRD in EmCTL-4. So EmCTL-1, EmCTL-2 and EmCTL-4 can be deduced binding with mannose in immune reactions. And the four C-type lectin genes shared 40% ,37% ,69% and 73% identity with the parallel C- type lectin genes in Macrobrachium rosenbergii ,existing in Palaemonidae. The CODEML program implemented in the PAML package was used to test for variations in selective pressures of shrimp and prawns C-type lectin genes with two CRDs, included the four genes acquired in this study, The result showed that the shrime and prawns lectin genes with two CRDs had undergone positive selection. According to the LTR test,3.8% of the sites were driven by positive selection in the M2a model ,while 5.6% of the sites were driven by positive selection in the M8 model. Phylogenetic analysis sh