摘要
为探讨黄颡鱼硒蛋白selenow2a、selenop2和selenot2基因之间的关系,采用3′/5′ RACE PCR克隆得到3个基因的cDNA全长,分别为891、1 998和1 432 bp,其中ORF长度分别为288、828和600 bp,编码95、275和219个氨基酸。在线工具SECISerach3对3个基因的cDNA序列分析结果显示,它们都含有可以编码硒代半胱氨酸的终止密码子,以及在3′非编码区存在SECIS元件。通过氨基酸序列比对和系统发育树分析,发现selenow2a、selenop2和selenot2基因预测得到的氨基酸序列与斑马鱼(Danio rerio)氨基酸相似性分别为82.24%、66.19%和79.45%,而与斑点叉尾鮰(Ictalurus punetaus)的氨基酸相似性分别为94.74%、68.50%和90.95%,在发育树上则显示为树杈相接近。采用实时荧光定量PCR检测3个硒蛋白基因的mRNA在黄颡鱼心脏、肝脏、肌肉、脑、肠、脾脏、精巢和卵巢组织中的表达,结果显示其mRNA表达水平呈现组织特异性。表明3个基因拥有硒蛋白家族的特征,但在组织表达上具有特异性。
硒(selenium)是脊椎动物维持细胞功能的正常行使并参与多种代谢活动必需的微量元素之
硒代半胱氨酸(selenocysteine,Sec) 是细胞中硒的主要形式,于 20 世纪 70 年末被发现且被归于第21种氨基酸,由终止密码子UGA编码,并通过特殊的共翻译机制嵌入到多肽链中。硒蛋白是含有Sec的蛋白,也是硒参与体内生理调控的关键生物分子,其特征是至少含有1个Sec,Sec的存在使得硒蛋白能够参与氧化还原反应。至今,在小鼠和人类中分别发现了24种和25种硒蛋
在斑马鱼中已经鉴定18个含Sec的硒蛋白基
试验用鱼购自武汉市当地农贸市场。在不投喂处理24 h后,选取健康、体形一致的体质量为(24.2±2.4) g的黄颡鱼分2组进行采样分析:第1组黄颡鱼取肝脏和卵巢组织用于基因cDNA克隆。第2组黄颡鱼样品用于测试心脏、肝脏、脑、脾脏、肌肉、精巢、卵巢和肠组织中黄颡鱼基因的表达水平。取样方法参照Zhao
凝胶回收试剂盒(Omega)、TRIzol试剂、逆转录试剂盒、3′/5′RACE PCR试剂盒、RT-PCR试剂盒,均购自TaKaRa公司;RNA提取实验中用到的异丙醇、乙醇等化学试剂均为分析纯(上海国药集团化学试剂有限公司)。
序列克隆参照文献[
根据GenBank数据库及转录组测序数据,设计扩增黄颡鱼硒蛋白基因序列的引物(
引物Primers | 序列Sequences (5'-3') |
---|---|
3'-RACE PCR | |
3' selenow2a-outer | GAGGTATCTGGCTTCGTTGG |
3' selenow2a-inner | GCCACCTTGCGTCATACTCT |
3' selenop2-outer | AGGACCAAGAACACTACCATT |
3' selenop2-inner | ACATGCTTCAGTTATCGCTCT |
3' selenot2-outer | GAATACTCCAGGTCTATCAGCC |
3' selenot2-inner | CTGCTTGCCATTGCTCTGA |
3' RACE outer | TACCGTCGTTCCACTAGTGATTT |
3' RACE inner | CGCGGATCCTCCACTAGTGATTTCACTATAGG |
5'-RACE PCR | |
5' selenow2a-outer | TGCCAACGAAGCCAGATAC |
5' selenow2a-inner | TAGCCTCATCCGCCACAAT |
5' selenop2-outer | GATTCCCTCTGCTGTTCGTT |
5' selenop2-inner | CCACGAATAGCGTTGAAGC |
5' selenot2-outer | GATTCATCTTGAGGTGGTTGTC |
5' selenot2-inner | TCAGAGCAATGGCAAGCAG |
5' RACE outer | CATGGCTACATGCTGACAGCCTA |
5' RACE inner | CGCGGATCCACAGCCTACTGATGATCAGTCGATG |
使用DNAStar 软件拼接序列片段,获得cDNA全长。拼接好的cDNA 序列通过NCBI进行Blast分析,以确定该序列命名是否正确。使用DNAStar软件,找出目的基因的开放阅读框(open reading frame,ORF),将其翻译成氨基酸序列,并使用Clustal-W软件进行氨基酸多序列比对和氨基酸相似性分析。在GUIDANCE网站 (http://guidance.tau.ac.il/)上对氨基酸多序列进行比对、剪切操
采用实时荧光定量PCR(qPCR)检测黄颡鱼硒蛋白基因的组织表达情
基因 Genes | 正向引物 Forward primer (5'-3') | 反向引物 Reverse primer (5'-3') | 登录号 Accession No. |
---|---|---|---|
selenow2a | TACGAACCCCGCTATCAGGA | ATCGTGGGCTTTCTGGATGG | ON109398 |
selenop2 | CAGGACGCTTTTTCAAGGGC | GGCAGCACAATGTGAAACGT | ON313812 |
selenot2 | CACACACAGGCAGAACAAGC | AGCTGGCTGATAGACCTGGA | ON109397 |
18S rRNA | AGCTCGTAGTTGGATCTCGG | CGGGTATTCAGGCGAGTTTG | KP938527 |
β-actin | GGACTCTGGTGATGGTGTGA | CTGTAGCCTCTCTCGGTCAG | EU161066 |
gapdh | GCCTCCTGCACCACAAACT | GCCTTGTTGAGCTTGACGAA | KP938522 |
tuba | TCAAAGCTGGAGTTCTCGGT | AATGGCCTCGTTATCCACCA | KP938526 |
b2m | GCTGATCTGCCATGTGAGTG | TGTCTGACACTGCAGCTGTA | KP938520 |
elfa | GTCTGGAGATGCTGCCATTG | AGCCTTCTTCTCAACGCTCT | KU886307 |
ubce | TCAAGAAGAGCCAGTGGAGG | TAGGGGTAGTCGATGGGGAA | KP938524 |
hprt | ATGCTTCTGACCTGGAACGT | TTGCGGTTCAGTGCTTTGAT | KP938523 |
本研究使用RT-PCR和RACE的方法获得了selenow2a、selenop2和selenot2的cDNA全长序列,长度分别为891、1 998和1 432 bp,其中ORF长度分别是288、828和600 bp,能够编码的氨基酸个数分别为95、275和219个(
基因 Genes | 登录号 Accession No. | 5' UTR/bp | ORF/bp | 3' UTR /bp | 全长/bp Full length | 蛋白/aa Protein |
---|---|---|---|---|---|---|
selenow2a | ON109398 | 128 | 288 | 475 | 891 | 95 |
selenop2 | ON313812 | 80 | 828 | 1090 | 1998 | 275 |
selenot2 | ON109397 | 108 | 660 | 664 | 1432 | 219 |

cDNA序列中存在编码Sec的终止密码子,在3′非编码区有SECIS元件序列(

图1 黄颡鱼selenow2a基因(A)、selenop2基因(B)和selenot2基因(C)的核苷酸序列及其氨基酸序列和功能域
Fig.1 Nucleotide sequence of the selenow2a(A),selenop2(B) and selenot2(C) gene of yellow catfish and its deduced amino acid sequence and predicted functional domain
编码硒代半胱氨酸的终止密码子以粗体显示,并将U用方框标记,在3'非编码区中预测的硒代半胱氨酸插入序列(SECIS)用下划线显示。The termination codon translated into selenocysteine is shown in bold and the U is marked with a box. The predicted selenocysteine insertion sequence (SECIS) in the 3′ untranslated region is shown as a underline.

图2 Selenow2a(A)、Selenop2(B)和Selenot2(C)氨基酸序列多重比对
Fig.2 Multiple amino acid sequence alignment of Selenow2a(A),Selenop2(B) and Selenot2(C)
Pf:黄颡鱼Pelteobagrus fulvidraco; Ip:斑点叉尾鮰 Ictalurus punctatus; Dr:斑马鱼 Danio rerio; Hs:智人 Homo sapiens; Rn:褐家鼠 Rattus norvegicus.
;使用序列上方的横线标记Rdx结构域和硫氧还蛋白样超家族;横线代表氧化还原序列CXXU(U为Sec,X为任意氨基酸);Sec(U)使用(★)代表;保守的U位置用椭圆标记。方框代表信号肽区域和富组氨酸区域。Horizontal line above the sequences denotes the Rdx structural domain and thioredoxin-like superfamily. The horizontal line below the sequence shows the redox sequence CXXU (U is Sec,X is any amino acid). Sec(U) is represented using (★). The conservative U position is marked with an ellipse. The boxes indicate signal peptide regions and histidine-rich regions.

图3 黄颡鱼硒蛋白SECIS元件分析与比较
Fig.3 Analysis and comparison of selenoprotein selenocysteine insertion sequence (SECIS)elements of selenoprotein genes from yellow catfish
A:结构图;B:SECIS元件序列。A:Structural diagrams;B:SECIS element sequences.
在进化关系上,黄颡鱼Selenow2a与斑点叉尾鮰的Selenow2a进化关系更加密切,而与斑马鱼Selenow2a、黄颡鱼同源蛋白Selenow、人类Selenow和大鼠Selenow关系较远(

图4 Selenow2a(A)、Selenop2(B)和Selenot2(C)氨基酸序列系统进化树
Fig.4 Phylogenetic tree based on Selenow2a (A),Selenop2 (B) and Selenot2 (C) sequences
硒蛋白来源于黄颡鱼和其他脊椎动物并标注其登录号。These selenoproteins were derived from yellow catfish and vertebrate,and their accession numbers were shown.
通过实时荧光定量PCR检测克隆的黄颡鱼selenow2a、selenop2和selenot2基因在8种组织中的mRNA表达水平,结果如

图5 硒蛋白基因selenow2a (A),selenop2 (B) 和selenot2 (C)在黄颡鱼不同组织中的分布和表达
Fig.5 The distribution and expression of selenoprotein genes selenow2a (A),selenop2 (B) and selenot2 (C) in different tissues in yellow catfish
H:心脏 Heart; B:脑 Brain; I:肠 Intestine; L:肝 Liver; M:肌肉Muscle; T:精巢 Testis; O:卵巢 Ovaries; S:脾脏 Spleen.柱上不同字母表示基因表达具有显著差异(P<0.05,单因素方差分析)。Various letters indicate different genes expressions(P<0.05,one-way ANOVA).
本研究克隆并获得3个黄颡鱼硒蛋白基因selenow2a、selenop2和selenot2,并在克隆得到的3个硒蛋白基因的cDNA序列中发现编码Sec的终止密码子和在3′非编码区发现SECIS元件,确定了克隆得到的基因属于硒蛋白家
克隆得到的selenow2a是黄颡鱼selenow的亚型基因。已有的研究报道了selenow在黄颡鱼多个组织中表达分布,并且发现在黄颡鱼的鳃中表达量最
Selenop是唯一已知的含有多个Sec的硒蛋白,主要将硒从肝脏传递到其他器
Selenot2和黄颡鱼Selenot具有同源关系,与Selenot具有类似的硒蛋白Rdx结构域和保守的CXXU氧化还原序列,暗示其具有氧化还原功能。氨基酸同源性和系统发育树的分析结果表明黄颡鱼Selenot2和斑马鱼Selenot2在进化中关系最近。黄颡鱼selenot2基因主要在黄颡鱼的心脏、肠、肝脏和肌肉中表达。相关研究表明,Selenot在保护金鱼(Carassius auratus)的心脏免受缺血再灌注(Ischemia-Reperfusion,IR)损伤时发挥了重要作
本研究通过RACE克隆获得3个黄颡鱼硒蛋白基因(selenow2a、selenot2和selenop2)并使用生物信息学技术推测出它们的氨基酸序列。通过与斑马鱼、斑点叉尾鮰对比分析,发现3个硒蛋白基因的核苷酸序列和氨基酸序列在鱼类中存在保守的序列,并且可以在人类和大鼠中找到,表明这些保守序列可能在不同物种的硒蛋白功能的稳定发挥中扮演重要角色。实时荧光定量PCR结果显示,3个硒蛋白基因在黄颡鱼体内均有表达,但不同的组织中表达水平差异显著,这可能与硒蛋白功能有关,还需要进一步深入的研究。
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