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2023 Volume 45 Issue 6
Article Contents

GONG Jing, ZHANG Wei, TANG Miao, et al. Cloning and Expression Analysis of BmHsp19.1 Gene in Silkworm Eggs[J]. Journal of Southwest University Natural Science Edition, 2023, 45(6): 109-115. doi: 10.13718/j.cnki.xdzk.2023.06.011
Citation: GONG Jing, ZHANG Wei, TANG Miao, et al. Cloning and Expression Analysis of BmHsp19.1 Gene in Silkworm Eggs[J]. Journal of Southwest University Natural Science Edition, 2023, 45(6): 109-115. doi: 10.13718/j.cnki.xdzk.2023.06.011

Cloning and Expression Analysis of BmHsp19.1 Gene in Silkworm Eggs

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  • Received Date: 09/10/2022
    Available Online: 20/06/2023
  • MSC: S882

  • Small heat shock proteins (sHsps) are the first line of cell defense. However, to date, the sHsps of Bombyx mori (BmsHsps), which are related to diapause of silkworm eggs, were not well studied. In order to better understand the role of BmsHsps in the process of diapause, the BmHsp19.1 gene, which is differentially expressed between diapause eggs and nondiapause eggs in the transcriptome, was studied by gene cloning, bioinformatics methods and PCR analysis. The results showed that the ORF of the BmHsp19.1 gene was 507 bp in length, encoding a total 168 amino acids, and the theoretical molecular weight of the protein was 19.06 kDa, which had a typical Hsp20 domain and belonged to the sHsps family. The BmHsp19.1 was up-regulated at day 3 to 7 after oviposition in diapause eggs, while it was up-regulated only at day 7 after oviposition in nondiapause eggs. Moreover, the expression level of BmHsp19.1 in diapause eggs was significantly higher than that in nondiapause eggs. It is speculated that BmHsp19.1 gene is involved in silkworm enter diapause, and plays an anti-stress role in protecting the body from injury. The results increased our understanding in the biological functions of BmHsp19.1, and may facilitate the sHsps study of other insects.
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Cloning and Expression Analysis of BmHsp19.1 Gene in Silkworm Eggs

Abstract: Small heat shock proteins (sHsps) are the first line of cell defense. However, to date, the sHsps of Bombyx mori (BmsHsps), which are related to diapause of silkworm eggs, were not well studied. In order to better understand the role of BmsHsps in the process of diapause, the BmHsp19.1 gene, which is differentially expressed between diapause eggs and nondiapause eggs in the transcriptome, was studied by gene cloning, bioinformatics methods and PCR analysis. The results showed that the ORF of the BmHsp19.1 gene was 507 bp in length, encoding a total 168 amino acids, and the theoretical molecular weight of the protein was 19.06 kDa, which had a typical Hsp20 domain and belonged to the sHsps family. The BmHsp19.1 was up-regulated at day 3 to 7 after oviposition in diapause eggs, while it was up-regulated only at day 7 after oviposition in nondiapause eggs. Moreover, the expression level of BmHsp19.1 in diapause eggs was significantly higher than that in nondiapause eggs. It is speculated that BmHsp19.1 gene is involved in silkworm enter diapause, and plays an anti-stress role in protecting the body from injury. The results increased our understanding in the biological functions of BmHsp19.1, and may facilitate the sHsps study of other insects.

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  • 昆虫种类众多、分布广泛,受益于昆虫在进化过程中生成的多种适应环境条件的能力,滞育便是昆虫周期性度过不良生存环境的一种策略. 与休眠不同,滞育是昆虫经年累月受到特定的刺激(例如光周期、温度等)[1],将这些外部信号转化为生物的一种特性,并遗传给后代. 进入滞育的昆虫,新陈代谢速率下降、应激耐受力增强、生长发育停滞[2].

    滞育可以发生在昆虫生长的任一阶段,按照不同的发育时期,可分为卵滞育、幼虫滞育、蛹滞育和成虫滞育[3]. 家蚕(Bombyx mori)是典型的卵滞育昆虫,遗传背景清晰,有重要的经济价值. 实际生产中,常使用一些特殊的处理法(如即时浸酸法、冷藏浸酸法)阻断或解除滞育[4],使其进入正常的发育状态. 此外,高浓度氧气处理滞育卵也能有效阻断蚕卵滞育[5-6]. 由于滞育对家蚕生长繁育的影响与蚕业生产相关,滞育机制还未完全解析,因此家蚕滞育研究一直是大家关注的焦点.

    热激蛋白(heat stress proteins,Hsps)广泛存在于原核、真核生物中,最早在果蝇(Drosophila melanogaster)中发现[7]. 当生物遭受外界胁迫(如高温)时,体内细胞通过诱导合成热激蛋白,作为分子伴侣促进蛋白质的完整性和细胞稳态,以抵御胁迫反应[8]. Hsps分子量差异较大,可分为sHsps(small heat shock proteins),Hsp60,Hsp70以及Hsp90[9]. 热激蛋白的存在反映了生物对环境中存在的某些极端应力的响应机制. 有研究表明,热激蛋白与昆虫的滞育联系紧密,在滞育期间热激蛋白基因表达产物通过增加、减少或者维持不变来促进昆虫在逆境中的生存[8].

    在前期研究中,我们通过对家蚕滞育卵与发育卵转录组的研究分析[6],发现了一些差异表达的热激蛋白基因,在这些基因中筛选出小分子热激蛋白BmHsp19.1基因,进行克隆、生物信息分析以及在不同发育状态蚕卵中的表达特征调查,对该基因的功能进行了初步推导. 该结果为解析BmHsp19.1功能提供了有价值的信息,为其他昆虫sHsps的研究提供了一些参考.

1.   材料和方法
  • 家蚕二化性品种大造(Dazao)由西南大学蚕桑纺织与生物质科学学院家蚕育种实验室提供. 对母代胚胎进行25 ℃长光照、15 ℃黑暗催青分别获得滞育卵、非滞育卵,对其中的滞育卵进行高浓度氧气处理、HCl处理,采集以上4种蚕卵产后0~7 d材料,用液氮速冻,保存于-80 ℃冰箱备用.

  • RNAiso Plus,反转录试剂盒,T4 DNA连接酶和pMD19-T载体,Takara;DNA聚合酶(2×Taq Master Mix),Novoprotein;胶回收试剂盒(Gel Extraction Kit),广州美基生物;氨苄霉素,上海生工;宿主菌BL21 (DE3)和大肠杆菌(Escherichia coli) 感受态菌株Trans1-T1,上海唯地生物;引物合成和测序,上海生工;纯氧气瓶,重庆强胜;HCl溶液,重庆科试.

  • 高浓度氧气处理:滞育卵产后20 h,放置于25 ℃氧气浓度为70%的三气培养箱中处理40 h.

    HCl处理:滞育卵产后20 h,室温25 ℃条件下在比重为1.100的HCl溶液中浸泡70 min,用流水洗净,晾干.

    期间收集两种处理产后2 d,3 d,5 d和7 d的蚕卵材料.

  • 利用报道过的BmHsp19.1基因序列在NCBI (http://www.ncbi.nlm.nih.gov/)以及SilkBase (http://silkbase.ab.a.u-tokyo.ac.jp/cgi-bin/)中进行检索,检索之后用引物设计软件Primer Premier (Version5.0)[10]设计BmHsp19.1荧光定量PCR (qRT-PCR)引物、克隆引物和内参引物sw22671[11] (表 1).

    BmHsp19.1载体构建实验中,以家蚕滞育卵7 d的cDNA作为模板进行PCR扩增. 循环参数为94 ℃预变性5 min;94 ℃变性30 s,55 ℃退火30 s,72 ℃延伸30 s,反应32个循环;72 ℃终延伸10 min. 产物经1.5%琼脂糖电泳后检测其大小,对目的DNA片段切胶回收,再与pMD19-T载体连接,将连接产物转化到感受态细胞中,通过菌液PCR筛选阳性克隆并进行测序鉴定.

    以产后0 h,20 h,2 d,3 d,5 d,7 d家蚕滞育卵、非滞育卵,产后2 d,3 d,5 d,7 d高浓度氧气处理、HCl处理的滞育卵的cDNA为模板开展qRT-PCR分析,qRT-PCR反应程序设定为94 ℃预变性1 min;94 ℃反应20 s,60 ℃反应40 s,30个循环. 每个样品3个生物学重复,相对定量(2-ΔΔCT法)计算基因表达量.

  • 利用在线网站预测BmHsp19.1的信号肽区域(https://services.healthtech.dtu.dk/service.php?SignalP-5.0)和磷酸化位点以及糖基化位点(https://prosite.expasy.org/),采用在线网站(http://smart.embl-heidelberg.de/) 预测结构域,采用在线网站(http://www.cbs.dtu.dk/services/TMHMM-2.0/)预测蛋白跨膜结构域,利用在线网站expasy (https://web.expasy.org/protscale/)对蛋白亲疏水性进行预测. 以BmHsp19.1为检索序列,采用NCBI(https://www.ncbi.nlm.nih.gov/)blast工具收集部分生物的sHsps序列,在TBtools软件中进行建树,建树方法为最大似然法,检验5 000次. 采用SilkDB 3.0(https://silkdb.bioinfotoolkits.net/main/species-info/-1)进行亚细胞定位,利用在线网站PSIPRED v3.3 (http://bioinf.cs.ucl.ac.uk/psipred/) 进行二级结构预测,利用在线网站Robetta(https://robetta.bakerlab.org/)对蛋白质的三维结构进行预测,用PyMOLWin软件制图并导出.

  • 使用GraphPad Prism 5.0软件对数据结果进行统计分析,采用two-way ANOVA方法检验比较不同样品的差异显著性(p<0.05).

2.   结果与分析
  • BmHsp19.1基因进行克隆,以家蚕品种大造滞育卵7 d的cDNA为模板,用基因的克隆引物进行PCR扩增,产物的大小采用1%琼脂糖凝胶电泳检测. 结果显示,在500~750 bp之间有1条特异性条带,与预期片段大小相符(图 1a). 对该PCR产物进行切胶回收,连接转化pMD19-T载体,筛选出阳性克隆进行测序,得到CDS长度为507 bp核苷酸序列,编码168个氨基酸,无信号肽结构,无跨膜结构域,在第56~152个氨基酸位具备Hsp20功能结构域,属于小分子热激蛋白家族(图 1b). 比对结果表明,BmHsp19.1基因克隆序列和家蚕SilkDB数据库预测基因序列一致.

  • BmHsp19.1蛋白预测的分子量为19.06 kDa,等电点为5.59,具有5个潜在的磷酸化修饰位点(T-29,S-56,T-79,S-117和S-143),无糖基化位点. 利用ProtScale软件进行蛋白亲疏水性分析,结果显示:BmHsp19.1蛋白亲水性氨基酸在整个肽链中的分布占比较多(图 2a),疏水性氨基酸相对较少,分别占总氨基酸的68.45%和31.55%. 23~41区域、81~89区域、128~138区域的氨基酸疏水性较强,其中,疏水性最强的氨基酸在第132位,分值为1.422;亲水性较强的氨基酸集中分布在9~22区域、34~35区域、42~69区域、71~77区域、90~122区域、139~152区域、154~164区域,其中亲水性最强的氨基酸在第96位,分值为-3.522. 通过PSIPRED v3.3和Robetta在线网站对蛋白的二级(图 2b)、三级结构进行预测(图 2c),其中,蛋白结构中无规则卷曲所占比例最大,为58.4%,β折叠占31.5%,α螺旋占10.1%.

  • 利用Mega X软件对20种不同物种的小分子热激蛋白构建系统进化树,结果显示,选用的物种形成脊椎动物和无脊椎动物两个大的分支,其中家蚕和野桑蚕的亲缘关系最近,然后再与其他鳞翅目昆虫聚在一起(图 3).

  • 为了调查家蚕BmHsp19.1基因在滞育卵、非滞育卵、高浓度氧气处理的滞育卵和HCl处理的滞育卵中的表达情况,采用qRT-PCR方法对其蚕卵进行分析(图 4). 结果表明:BmHsp19.1基因在滞育卵和非滞育卵产后0~2 d的表达量较小,差异不大;滞育卵的表达量在产后3~7 d上调,显著高于非滞育卵. 在滞育卵、高氧处理组和HCl处理组的比较中,BmHsp19.1基因的表达量也是在滞育卵中产后3 d开始上调,显著高于其余处理组,并持续到产后7 d. 说明BmHsp19.1基因主要在蚕卵进入滞育过程的后期高量表达,暗示该基因可能在进入滞育过程中起到了很重要的作用.

3.   讨论
  • 本研究中我们聚焦可能与滞育有关的Hsps家族蛋白,这类蛋白通常在昆虫经历高温、寒冷、缺氧等外界不利条件时产生并发挥作用,其中Hsp60,Hsp70和Hsp90的分子量较大,依赖于ATP发挥作用;而sHsps家族蛋白,其分子量介于12~43 kDa之间,通常在30 kDa以下,蛋白有保守的二级结构和蛋白结构域,不依赖ATP发挥作用[8, 12]. 本文中鉴定的BmHsp19.1基因,其蛋白分子量为19.06 kDa,具有典型的Hsp20功能结构域,属于小分子热激蛋白家族.

    滞育是昆虫经历的一个特殊的生理环境,是生命活动由旺盛到几乎停滞的过程[13]. 由于呼吸的减弱生物会进入到一个生理性缺氧的状态,这与外界条件缺氧环境很相似. 已有研究发现,蟋蟀(Allonemobius socius)在卵滞育时具有代谢减少64%的特征,Hsp20.7Hsp90的mRNA表达量相对于非滞育的卵减少,而Hsp70的mRNA表达量没有变化[14-15]. 苜蓿切叶蜂(Megachile rotundata)滞育蛹中Hsp70的表达量明显上调,但Hsc70Hsp90表达量的变化很小[16]. 有意思的是,果蝇成虫在缺氧过程中会上调至少4个Hsps基因,包括Hsp23Hsp67BcHsp68Hsp40,其中Hsp23对缺氧最敏感[17]. 受缺氧影响的肥须麻蝇(Sarcophaga crassipalpis)成虫增加了Hsps基因的表达:Hsp70对缺氧反应最迅速,并且表现出最大的表达,其次是sHsps基因(Hsp18Hsp23Hsp25),然后是Hsp40Hsp60 [18]. 从中可以看出,无论是滞育还是缺氧环境,热激蛋白都做出了压力反应,其中小热激蛋白表现为普遍上调.

    家蚕在胚胎早期进入滞育,以滞育卵的形式度过寒冷的冬季. 科研工作者通过组学的方法对家蚕中的Hsps进行了广泛的鉴定[6, 19-20],其中与家蚕滞育相关的HspsHsp60Hsp70DnaJHsp83Hsp90sHspsHsp12.2-likeHsp19.1Hsp19.9Hsp20.1Hsp20.4Hsp20.8Hsp23.7. 由于滞育过程中能量代谢被抑制,产生的ATP显著下降,此时不依赖于ATP的sHsps在滞育过程中大量积累. 有研究表明Hsp12.2-likeHsp19.5在滞育卵中上调表达[6, 21],本研究中的BmHsp19.1基因在家蚕滞育进入过程中也呈现出上调表达的趋势. 这些sHsps与细胞中存储的蛋白质结合,可以起到防止蛋白不可逆变性的保护作用,这是细胞在滞育期间抵御压力引起的蛋白质损失的首要反应[22-23]. sHsps反应迅速还在于其可以通过转录后修饰,如磷酸化等来调节蛋白活性,无需从头合成蛋白. 在这方面研究最广泛的例子是人类Hsp27,其N末端区域内有3个磷酸化位点(Ser-15,Ser-78和Ser-82),通过丝裂原活化蛋白激酶级联调控进行修饰[12, 24],而本研究中BmHsp19.1预测的磷酸酸化位点多达5个(T-29,S-56,T-79,S-117和S-143),暗示该蛋白可能通过蛋白修饰活化进而发挥功能. 有研究表明sHsps在正常和应激条件下,细胞内定位是不同的[25-26],而该蛋白在不同条件下的亚细胞定位,有待进一步实验证实.

    综上所述,本研究成功地对BmHsp19.1基因进行了鉴定和在蚕卵中的表达分析,该结果丰富了家蚕Hsps基因家族的研究信息,下一步将获取较纯的BmHsp19.1蛋白,作为研究滞育卵和非滞育卵差异的候选基因,后续可采用RNAi干扰或基因编辑的方法对其开展功能研究.

Figure (4)  Table (1) Reference (26)

Catalog

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