南京农业大学学报  2016, Vol. 39 Issue (4): 632-639   PDF    
http://dx.doi.org/10.7685/jnau.201509030
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文章信息

金雯雯, 王德迪, 潘增祥, 决肯, 李齐发
JIN Wenwen, WANG Dedi, PAN Zengxiang, JUE Ken, LI Qifa
湖羊和巴什拜羊BMP15基因c.-1760C>A变异与启动子区活性的关系
c.-1760C>A variant of BMP15 gene and its association with the promoter activity in Hu sheep and Bashibai sheep
南京农业大学学报, 2016, 39(4): 632-639
Journal of Nanjing Agricultural University, 2016, 39(4): 632-639.
http://dx.doi.org/10.7685/jnau.201509030

文章历史

收稿日期:2015-09-25
湖羊和巴什拜羊BMP15基因c.-1760C>A变异与启动子区活性的关系
金雯雯1, 王德迪1, 潘增祥1, 决肯2, 李齐发1    
1. 南京农业大学动物科技学院, 江苏 南京 210095;
2. 新疆农业大学动物科学学院, 新疆 乌鲁木齐 830052
摘要[目的] 为了解湖羊和巴什拜羊骨形态发生蛋白15(BMP15)基因编码区和5'调控区(5'UTR)序列特征与差异,检测其SNPs(single nucleotide polymorphisms)并探索其功能。[方法] 利用克隆测序技术获得湖羊和巴什拜羊BMP15基因编码区和5'UTR序列,运用生物信息学方法分析其序列特征;采用DNA池测序法筛选湖羊和巴什拜羊BMP15基因SNPs,直接测序法检测SNPs位点多态性;采用荧光素酶报告基因系统检测启动子区活性。[结果] 湖羊和巴什拜羊BMP15基因编码区序列长度均为1182 bp,编码393个氨基酸,编码蛋白含有典型的TGF-β结构域;湖羊和巴什拜羊BMP15基因编码区序列的同源性为99.92%,发现1个SNP位点。获得1806 bp湖羊和巴什拜羊BMP15基因5'调控区序列,发现5个SNPs位点。BMP15基因c.-1760C>A位点多态性分析发现湖羊群体中均为CC基因型,巴什拜羊群体中有CC、CA和AA 3种基因型,等位基因C和A频率分别为0.7981和0.2019。启动子区活性检测显示CC型启动子区活性明显高于AA型。[结论] 湖羊和巴什拜羊BMP15基因编码区序列高度保守,c.-1760C>A变异可能影响BMP15基因启动子区活性。
关键词BMP15基因     湖羊     巴什拜羊     SNPs     启动子区活性    
c.-1760C>A variant of BMP15 gene and its association with the promoter activity in Hu sheep and Bashibai sheep
JIN Wenwen1, WANG Dedi1, PAN Zengxiang1, JUE Ken2, LI Qifa1     
1. College of Animal Science and Technology, Nanjing Agricultural University, Nanjing 210095, China;
2. College of Animal Science, Xinjiang Agricultural University, Urumqi 830052, China
Abstract: [Objectives] To identify the characterization of 5'-untranslated region (5'-UTR) and coding region (CDS) sequence of bone morphogenetic protein15 (BMP15) gene between Hu sheep and Bashibai sheep,we analyzed the single nucleotide polymorphism (SNP) in BMP15 gene and explored its function.[Methods] The coding and 5'-untranslated sequence of BMP15 gene were obtained using cloning and sequencing technology and we used the bioinformatics methods to analyze its sequence characterization in the Hu sheep and Bashibai sheep. The SNPs of BMP15 gene were screened using DNA pool technology and were detected using sequencing method. The activity of BMP15 promoter was investigated using dul-luciferase reporter assay system.[Results] The full length coding region of BMP15 were both 1 182 bp in Hu sheep and Bashibai sheep,which encoded 393 amino acids and contained TGF-β domain. The coding regions of BMP15 in Hu sheep shared similarities of 99.92% to Bashibai sheep,in which we detected one SNP in Hu sheep and Baishibai sheep. A total of 1 806 bp sequence of 5'-UTR was obtained,where we identified five SNPs in Hu sheep and Baishibai sheep. There was one genotype (CC) and three genotypes (CC,CA,AA)(c.-1760C>A) in the 5'-UTR of BMP15 gene in Hu sheep and Bashibai sheep,respectively. Further analysis showed that the frequency of C allele and A allele were 0.798 1 and 0.201 9,respectively. The luciferase reporter assay indicated that the promoter activity of genotype CC was obviously high than genotype AA.[Conclusions] The coding region sequences of BMP15 gene are highly conservative between Hu sheep and Bashibai sheep. The SNP (c.-1760C>A) may be involved in the effect on the promoter activity of BMP15 gene.
Keywords: BMP15 gene     Hu sheep     Bashibai sheep     single nucleotide polymorphisms (SNPs)     promoter activity    

骨形态发生蛋白15(bone morphogenetic protein,BMP15),又叫生长分化因子9B(growth differentiating factor 9B,GDF9B),是转化生长因子TGF-β超家族中的重要成员,也是第一个在绵羊中发现的、影响高繁殖力性状(排卵数和产羔数)的主效基因[1, 2]。绵羊BMP15基因位于X染色体上,在绵羊卵巢组织中高表达,Northern blot和原位杂交分析发现其在卵巢卵母细胞中特异性表达,是绵羊卵巢卵泡发育必需的,在卵泡发育、成熟、排卵、受精和妊娠等过程中发挥关键作用[3, 4]。Davis等[1]通过对一个11胎产33个羔羊的Romney母羊进行家系分析发现了一个影响排卵数的主效基因,因其位于X染色体上故命名为FecX,高繁殖力等位基因命名为FecXI,并最终定位于BMP15基因上[5]。随后,在Hanna羊、Romney羊、Belclare羊、Cambridge羊、Lacaune羊和Rasa Aragonesa羊等国外绵羊品种中又发现了5个不同的高繁殖力突变位点,分别命名为FecXHFecXGFecXBFecXLFecXR[5, 6, 7, 8]。2013年,Demars等[9]通过全基因组关联分析法在法国Grivette羊和波兰Olkuska羊BMP15基因中发现了2个影响高繁殖力性状的非同义突变位点,分别命名为FecXGrFecXO。研究者还发现了一些未命名的、与绵羊繁殖性状关联的BMP15基因编码区突变位点如G906A[10]等,因此BMP15基因也是目前发现高繁殖力SNPs最多的主效基因。

湖羊是我国著名的高繁殖力绵羊品种,但目前在国外绵羊品种中发现的高繁殖力SNPs在湖羊中均未发现多态性[11]。本试验拟以高繁殖力绵羊品种湖羊和低繁殖力绵羊品种巴什拜羊为研究对象,用克隆测序技术获得绵羊BMP15基因编码区和5′UTR序列,用生物信息学方法分析序列特征,用DNA池测序法筛选BMP15基因编码区和5′调控区SNPs位点,以期为绵羊高繁殖力的标记辅助选择提供科学依据。

1 材料与方法 1.1 试验材料 1.1.1 试验动物

试验用湖羊由江苏省苏州种羊场提供,共92只;巴什拜羊采自新疆裕民县,共52只。每个个体采取耳组织样,置于液氮中带回实验室,-20 ℃保存。

1.1.2 主要试剂

DNA提取和PCR所用试剂购于TaKaRa公司;pGL-3质粒购自Promega公司;COV-434细胞购自于上海吉凯公司;大肠杆菌DH5α菌株购于天根生化科技有限公司。

1.2 试验方法 1.2.1 DNA提取

采用酚/氯仿抽提法提取耳组织样DNA,-20 ℃保存。

1.2.2 引物设计

根据GenBank数据库中绵羊BMP15基因全序列(NC_019484.1),用Primer Premier 5.0软件设计4对引物,引物具体信息详见表 1。引物由北京六合华大基因公司合成。

表 1 引物序列及PCR参数 Table 1 Primer sequences and the parameters of PCR reaction
引物编号Primer No.引物对序列(5′→3′)Primer pairs sequences退火温度/℃Annealingtemperature长度/bpLength用途Usage
P1GAGCCTGGATGCTGTTAC/GGCTAAGCCTTTCAGGAC56928CDS clone
P2TCAAGGCTGCTTGTCAGT/GCTGAAGGCAAGGAATAG561 089CDS clone
P3GCCCTGATGCCTCCAGTAACT/GCGGCTTCCTCTGCTGCTT581 1745′UTR clone
P4ACCAAATCACATTCCCATCA/ACCAGGGCAACAGGATTTC561 0585′UTR clone
P5CGGGGTACCACCAAATCACATTCCCATCA/CCCAAGCTTCTTGGTCCCTGGCATGTA53434Construction ofrecombinant vector
1.2.3 PCR扩增和克隆测序

PCR程序:98 ℃30 s;98 ℃10 s,退火30 s,72 ℃ 60 s,共32个循环;72 ℃ 7 min,4 ℃保存。产物用1.5 g·L-1的琼脂糖凝胶电泳检测,回收纯化后与pMD19-T Vector(TaKaRa公司)连接,并转化到DH5α感受态细胞中。挑取阳性克隆,采用试剂盒提取质粒,送苏州金唯智生物公司进行测序。

1.2.4 序列分析

绵羊BMP15基因编码区序列获得方法和所用软件见文献[12]。绵羊BMP15基因启动子区预测采用在线软件Berkeley Drosophila Genome Project(http://www.fruitfly.org/seq_tools/promoter.html),转录因子结合位点采用TFSEARCH软件(http://mbs.cbrc.jp/research/db/TFSEARCH.html),CpG岛预测采用CpG Islands软件(http://www.ualberta.ca/stothard/javascript/cpg_islands.html)。

1.2.5 SNP筛选

利用引物P1~P4,以湖羊和巴什拜羊DNA池为模板进行序列PCR扩增,PCR产物直接送苏州金唯智生物公司测序。运用Chromas 231软件分析序列峰图,筛选SNPs位点。

1.2.6 基因分型

根据SNPs筛选结果,选择BMP15基因5′UTR中的c.-1760C>A位点为研究对象进行测序分型。利用PowerStats v12.0计算基因频率、基因型频率、多态信息含量(PIC)和杂合度(He)等。

1.2.7 载体构建

采用Primer Premier 5.0软件设计包含c.-1760C>A位点的引物P5,上、下游引物分别包含限制性内切酶KpnⅠ和Hind Ⅲ酶切位点(表 1)。分别以CC、AA型个体DNA为模板进行PCR扩增,PCR产物用KpnⅠ和Hind Ⅲ双向酶切,并回收酶切片段,将回收的片段克隆到经KpnⅠ和Hind Ⅲ双向酶切的pGL3双荧光素酶报告基因载体中,转染感受态细胞DH5α,构建c.-1760C>A位点不同纯合型启动子荧光素酶报告基因重组质粒。采用双酶切鉴定法和直接测序进行确认。

1.2.8 细胞培养、转染和荧光素酶活性分析

将COV-434细胞接种至细胞培养瓶,于37 ℃恒温细胞培养箱中培养。传代培养,待细胞汇合度达到80%时,采用Lip2000脂质体转染。转染分对照组和试验组,每组4个重复,试验组加入pGL3-C或pGL3-A重组质粒,对照组加入pGL3空载质粒。24 h后收集细胞,检测Renilla荧光素酶活性(R值)。

1.3 数据处理

运用SPSS 18.0软件对数据进行单因素方差分析。

2 结果与分析 2.1 湖羊和巴什拜羊群体BMP15基因编码区和5′调控区PCR扩增

利用引物P1~P4对湖羊、巴什拜羊基因组DNA进行PCR扩增,PCR产物用琼脂糖凝胶电泳检测,结果表明扩增片段与目的片段大小一致且特异性好(图 1)。测序发现扩增片段长度分别为928、1 089、1 174和1 058 bp,与预期扩增长度一致。

图 1 绵羊BMP15基因片段扩增产物电泳图谱 Fig. 1 Agarose gel photograph of BMP15gene in sheep M. DNA marker(DL2000);1~4. P1~P4引物扩增片段 Fragments amplified of primer P1-P4
2.2 湖羊和巴什拜羊群体BMP15基因编码区序列分析 2.2.1 核苷酸序列分析

将引物P1和P2扩增片段的测定序列进行拼接,获得完整的湖羊和巴什拜羊BMP15基因编码区序列(图 2)。预测ORF发现湖羊和巴什拜羊BMP15基因编码区长度均为1 182 bp,两者同源性为99.92%。湖羊和巴什拜羊BMP15基因编码区核苷酸序列与人、小鼠、大鼠、牛、猪等哺乳动物的同源性分别为81.57%、81.48%,77.83%、77.75%,77.33%、77.24%,98.31%、98.23%和90.30%、90.21%,但与鸡的同源性仅为46.34%和46.26%。

图 2 湖羊和巴什拜羊BMP15基因编码区序列与预测的氨基酸序列 Fig. 2 CDS sequence and deduced amino acid sequence of BMP15 gene in Hu sheep and Bashibai sheep 画框碱基G在巴什拜羊中发生突变(G>A)。The base G in the box had a mutation(G>A)in Bashibai sheep.
2.2.2 氨基酸序列分析

湖羊和巴什拜羊BMP15基因均编码一个含393个氨基酸的蛋白(图 2),两者氨基酸序列的同源性为100%。比对分析发现湖羊(巴什拜羊)BMP15蛋白氨基酸序列与人、小鼠、大鼠、牛、猪等哺乳动物的同源性分别为73.42%、68.45%、68.45%、86.55%和87.31%,但与鸡的同源性仅为39.09%。蛋白理化性质分析发现湖羊和巴什拜羊BMP15蛋白的相对分子质量为4.49×104,理论等电点(pI)为9.46,体外半衰期为30 h,不稳定系数48.05,疏水性均值(GRAVY)为-0.312,说明湖羊和巴什拜羊BMP15蛋白具有较强的亲水性。信号肽预测发现湖羊和巴什拜羊BMP15蛋白含有信号肽,位于M1~M24,可能的剪切位点位于24和25位氨基酸之间(VQM~TQ D=0.713,D-cutoff=0.450)。跨膜分析表明BMP15没有跨膜区,处于细胞膜外部。结构域预测发现BMP15具有典型的TGF-β结构域(图 3)。三级结构预测发现绵羊BMP15蛋白主要由2个α-螺旋和6个β-折叠组成(图 4)。

图 3 湖羊和巴什拜羊BMP15氨基酸序列与人、小鼠的同源性比较 Fig. 3 Identical alignments of BMP15 amino acid sequence in Hu sheep and Bashibai sheep with human and mouse

图 4 湖羊和巴什拜羊BMP15蛋白的三级结构 Fig. 4 Space structure prediction analysis of BMP15 protein in Hu sheep and Bashibai sheep
2.3 湖羊和巴什拜羊群体BMP15基因5′调控区序列分析

对引物P3和P4扩增产物的测序结果进行拼接,获得湖羊和巴什拜羊BMP15基因5′调控区序列,序列总长均为1 806 bp(图 5),位于-1 806 nt至-1 nt。启动子序列预测显示在湖羊和巴什拜羊BMP15基因-1 617 nt~-1 568 nt处存在可能的启动子区(分值为0.90),但在启动子区中未发现TATA框和CAAT框。运用CpG岛生物在线软件分析,未发现标准CpG岛的存在。转录因子结合位点预测到一系列潜在的转录因子结合位点存在于湖羊和巴什拜羊BMP15基因5′调控区中,如热应激转录因子(HSF)、尾型同源盒A(CdxA)、八聚体结合转录因子1(OCT-1)、性别决定区(SRY)、性别决定区域盒5(SOX-5)、GATA-1、激活蛋白1(AP-1)、腈水解酶家族成员2(NIT-2)、GATA-2等(图 5)。

图 5 绵羊BMP15基因5′调控区序列 Fig. 5 The 5′UTR sequences of BMP15 gene in sheep 下划线代表潜在启动子区位置;方框代表转录因子结合位点;黑三角代表碱基突变位点。
The underline was a potential promoter region;the boxes were binding sites of transcription factors;the black triangles were SNP sites.
2.4 湖羊和巴什拜羊群体BMP15基因SNP位点筛选

根据DNA池测序的序列峰图,在湖羊和巴什拜羊群体BMP15基因编码区和5′调控区中共发现6个变异位点(表 2),其中在编码区仅发现1个变异位点(6355G>A),但未引起氨基酸改变,为同义突变位点。在湖羊和巴什拜羊群体BMP15基因5′调控区5个变异位点中,c.-1760C>A位点导致转录因子结合位点的改变。

表 2 湖羊和巴什拜羊群体BMP15基因SNP位点 Table 2 Nucleotide polymorphisms within the BMP15 gene of Hu sheep and Bashibai sheep
编号No.位置Position变异Variation主要等位基因Major allele编号No.位置Position变异Variation主要等位基因Major allele
16 355G>AG4-1 146C>TC
2-609G>AG5-1 548G>AG
3-1 145G>AG6-1 760C>AC
2.5 绵羊BMP15基因c.-1760C>A 位点的多态性分析

采用直接测序法对湖羊和巴什拜羊群体BMP15基因c.-1760C>A位点的多态性进行检测,结果在湖羊中只发现1种基因型即CC型,而在巴什拜羊的c.-1760C>A位点发现3种基因型:CC、CA和AA型(图 6)。湖羊和巴什拜羊群体BMP15基因c.-1760C>A位点的基因型频率、基因频率、多态信息含量和杂合度详见表 3。由表 3可见:在湖羊和巴什拜羊群体中CC型为优势等位基因型,C为优势等位基因。巴什拜羊群体BMP15基因c.-1760C>A位点的杂合度(He)和多态信息含量(PIC)分别为0.355 5、0.359 0。卡方检验发现该位点处在Hardy-Weinberg不平衡状态,说明在巴什拜羊培育过程中可能受到了人工选择和选育的影响。

图 6 绵羊BMP15基因c.-1760C>A位点3种基因型测序图 Fig. 6 Heterozygous and homozygous sequencing diagram of c.-1760C>A locus in BMP15 gene of sheep

表 3 绵羊BMP15基因c.-1760C>A 位点遗传多样性 Table 3 The genetic diversity index of c.-1760C>A in BMP15 gene of sheep
品种Breed基因型频率 Genotype frequency等位基因频率 Allele frequencyPICHe
CCCAAACA
湖羊Hu sheep1(92)0(0)0(0)10
巴什拜羊Bashibai sheep0.615 4(32)0.365 4(19)0.019 2(1)0.798 10.201 90.359 00.355 5
2.6 c.-1760C>A 位点突变对BMP15基因启动子区活性的影响

利用引物P5对绵羊BMP15基因c.-1760C>A位点CC型和AA型个体进行PCR扩增,扩增产物电泳结果见图 7。PCR产物克隆入双荧光素酶报告基因载体pGL3中,重组质粒用限制性内切酶KpnⅠ和Hind Ⅲ进行双酶切鉴定,结果发现目的片段已连接到载体中(图 7-A),测序发现连接到载体中的目的片段序列完全正确,说明启动子区双荧光素酶报告基因载体构建成功,并分别命名为pGL3-C和pGL3-A。细胞转染和荧光素酶活性分析发现pGL3-C活性明显高于pGL3-A活性,但未达到显著水平(P=0.069)(图 7-B),说明c.-1760C>A位点突变对绵羊BMP15基因的启动子区活性有一定的影响。

图 7 c.-1760C>A 位点突变对BMP15基因启动子区活性的影响(** P<0.01) Fig. 7 The effect of the SNP(c.-1760C>A)on the promoter activity of BMP15 gene A. 重组报告质粒的酶切鉴定Identification of recombinant vectors by restriction enzymes(M. DNA marker(DL2 000);1. P5引物扩增片段Fragments amplified of primer P5;2. pGL3-C型重组质粒pGL3-C recombinant vector;3. pGL3-A型重组质粒pGL3-A recombinant);B. 不同基因型启动子活性Promoter activity analysis
3 讨论

绵羊是一个单胎物种,但也有极少数绵羊品种表现出多胎现象,如澳大利亚的Booroola羊、英国的Cambridge羊和中国的湖羊等,因此绵羊是哺乳动物高繁殖力研究的理想模型。目前在绵羊中鉴定出多个控制高繁殖力性状的主效基因,BMP15基因就是其中的一个[2]。BMP15在哺乳动物卵巢卵母细胞中特异表达,在绵羊卵巢颗粒细胞增殖、卵泡发育和排卵过程中发挥关键作用[4, 13]。本试验通过克隆测序获得了2个绵羊品种(湖羊和巴什拜羊)BMP15基因编码区全序列,发现其与其他绵羊品种、哺乳动物其他物种在序列、蛋白的理化性质、结构域和高级结构等方面均具有高度保守性,推测湖羊和巴什拜羊BMP15基因与其他物种一样,在卵泡发育过程中发挥关键作用。另外,本试验在湖羊(高繁殖力品种)和巴什拜羊(低繁殖力品种)BMP15基因编码区序列中发现1个SNP位点(6355 G>A),但未引起氨基酸改变;而在其他绵羊品种中发现的FecXIFecXHFecXGFecXBFecXLFecXRFecXGrFecXO等高繁殖力等位基因在湖羊中也不存在,说明BMP15基因编码区突变可能与湖羊高繁殖力性状无关。

BMP15在绵羊卵巢组织中高表达,特别是在卵母细胞中特异表达,高繁殖力品种(群体)卵巢组织或卵泡中表达水平显著高于低繁殖力品种(群体)[14, 15]。但目前关于绵羊BMP15基因表达调控的研究较少[16],其5′调控区的研究还未见报道。5′调控区是各种转录因子结合的区域,不同转录因子对基因的表达调控起着不同作用,基因表达是这些转录因子共同作用的结果[17]。本试验通过克隆测序获得了湖羊和巴什拜羊BMP15基因5′调控区,预测到多个转录因子如HSF、CdxA、OCT-1、SRY、Sp1、SOX-5、GATA-1、AP-1、NIT-2、GATA-2等结合位点。OCT-1能够结合在DHS3上使促卵泡激素受体(FSHR)的转录沉默,从而影响卵泡颗粒细胞的增殖分化[18];Sp1对孕酮在排卵期前鼠卵巢颗粒细胞的作用新靶点——X连锁淋巴细胞调节基因5c-like(Xlr5c-like),起到一定的调控作用[19]。绵羊BMP15基因5′调控区的鉴定为以后研究其表达调控奠定了基础。

目前关于绵羊BMP15基因SNPs的研究主要集中在编码区,但这些编码区SNP多态与湖羊高繁殖力均无显著关联[11, 20]。本试验对湖羊和巴什拜羊BMP15基因5′调控区突变进行了筛选,在-1 760 nt处发现C>A突变,该位点的基因频率在湖羊和巴什拜羊群体中表现出差异,且影响BMP15基因的启动子区活性。转录因子结合位点预测发现BMP15基因c.-1760C>A突变增加了一个新的转录因子GATA-2结合位点。GATA-2是GATA转录因子家族中的重要成员,含有典型的锌指结构,主要通过与靶基因启动子区GATA基序(motif)结合,正向或负向调控靶基因的表达[21, 22]。研究发现转录因子GATA-2可通过与类固醇激素合成关键酶CYP11A1和StAR的基因启动子区结合调节小鼠卵巢和胎盘中靶基因启动子区活性和基因转录[23, 24]。同时,GATA-2对促性腺激素的分泌是必要的[25],可见其与动物卵泡发育、繁殖功能等密切联系。因此,我们推测c.-1760C>A突变可能通过影响其与转录因子GATA-2的结合来调控绵羊BMP15基因启动子区活性和基因转录。

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