中国水产科学  2022, Vol. 29 Issue (03): 421-434  DOI: 10.12264/JFSC2021-0382
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引用本文 

邵嘉棋, 杜金星, 雷彩霞, 李胜杰, 董传举, 张猛, 李学军. 基于转录组测序筛选大口黑鲈食性驯化相关基因和SNP标记[J]. 中国水产科学, 2022, 29(3): 421-434. DOI: 10.12264/JFSC2021-0382.
SHAO Jiaqi, DU Jinxing, LEI Caixia, LI Shengjie, DONG Chuanju, ZHANG Meng, LI Xuejun. Development of genes and SNP markers related to food domestication based on largemouth bass transcriptome[J]. Journal of Fishery Sciences of China, 2022, 29(3): 421-434. DOI: 10.12264/JFSC2021-0382.

基金项目

国家自然科学基金项目(32102776);中央级公益性科研院所基本科研业务费项目(2021SJ-XK4,2021SJ-CG1);广州市科技计划项目(202002020018).

作者简介

邵嘉棋s(1997–),女,硕士研究生,研究方向为水产遗传育种. E-mail: jq0822shao@163.com

通信作者

李胜杰,研究员,研究方向为水产生物技术与遗传育种. E-mail: ssjjli@163.com

文章历史

收稿日期:2021-08-22
修改日期:2021-10-22
基于转录组测序筛选大口黑鲈食性驯化相关基因和SNP标记
邵嘉棋1,2,杜金星2,雷彩霞2,李胜杰2,董传举1,张猛1,李学军1,     
1. 河南师范大学水产学院,河南 新乡 453007
2. 中国水产科学研究院珠江水产研究所,农业农村部热带亚热带水产资源利用与养殖重点实验室,广东 广州 510380
摘要:采用人工驯食方法改变肉食性鱼类的食性是其养殖过程中的关键环节,但目前对鱼类食性驯化的分子遗传机制了解甚少。为了获得大口黑鲈(Micropterus salmoides)食性驯化相关基因和标记,本研究以1月龄大口黑鲈“优鲈3号”为研究对象,对驯化其摄食人工配合饲料后的易驯食组和不易驯食组脑和肝脏组织进行转录组测序和分析。结果表明,共获得51255万条高质量clean reads,注释到27930个基因,易驯食组和不易驯食组脑和肝脏组织中差异表达基因分别为362和3389个,其中参与调控食性驯化的基因64个,如周期蛋白(period, PERs)、视紫红质(rhodopsin, RHO)、视黄醇脱氢酶(retinol dehydrogenase, RDHs)、角鲨烯单加氧酶(squalene monooxygenase, SQLE)、胆汁酸输出泵(bile salt export pump, BSEP)、瘦素(leptin, LEP)等主要分布在昼夜节律、光传导、视黄醇代谢、类固醇生物合成、胆汁分泌和PI3K-AKT信号通路中,这些通路在环境适应、视觉系统、消化代谢、食欲控制等生物过程中发挥重要作用。从不易驯食组和易驯食组的差异表达基因中筛选出21465个SNP标记,进一步采用SNaPshot技术对其中14个SNP标记在易驯食和不易驯食群体中进行验证并与驯食性状进行关联分析,结果显示仅RDH12基因中的chr15-A+8322808G位点与驯食性状存在显著关联性(P<0.05),其AA基因型为易驯食个体的优势基因型。本研究分别获得了与大口黑鲈驯食性状相关基因64个和SNP标记1个,为分子标记辅助大口黑鲈食性驯化遗传改良提供了候选基因和标记。
关键词大口黑鲈    驯食性状    转录组测序    差异表达基因    单核苷酸多态性    
Development of genes and SNP markers related to food domestication based on largemouth bass transcriptome
SHAO Jiaqi1,2,DU Jinxing2,LEI Caixia2,LI Shengjie,2,DONG Chuanju1,ZHANG Meng1,LI Xuejun1    
1. College of Fisheries, Henan Normal University, Xinxiang 453007, China
2. Key Laboratory of Tropical & Subtropical Fishery Resource Application & Cultivation, Ministry of Agriculture and Rural Affairs; Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China
Abstract:Artificial domestication of feeding habits of carnivorous fish is a key step in their breeding and production, and the molecular mechanism of food domestication is poorly understood. In this study, a new strain of largemouth bass (Micropterus salmoides), "Youlu No. 3" , was used as the research object, and transcriptome sequencing of the brain and liver tissues from a domesticated and non-domesticated group was performed to obtain genes and markers related to food domestication. In total, 51255 million high-quality clean reads were obtained and mapped to 27930 genes. The results showed that there were 362 and 3389 differentially expressed genes in the brain and liver tissues, respectively. The 64 genes involved in food domestication regulation, such as period (PERs), rhodopsin (RHO), retinol dehydrogenase (RDHs), squalene monooxygenase (SQLE), bile salt export pump (BSEP), and leptin (LEP), were mainly distributed in circadian rhythm, phototransduction, retinol metabolism, steroid biosynthesis, bile secretion, and the PI3K-AKT signaling pathways. These pathways play an important role in environmental adaptation, visual system function, digestion and metabolism, and appetite control. Furthermore, 21465 SNP markers were screened from the differentially expressed genes in the non-domesticated group and domesticated group. The SNaPshot technique was used to verify the 14 SNP markers that were randomly selected, and their association with food domestication was analyzed. The results showed that only the chr15-A+8322808 marker in the RDH12 gene was found to be significantly associated with domestication traits (P<0.05), and its AA genotype was the dominant genotype in easily domesticated individuals. Overall, 64 differentially expressed genes and one SNP marker related to food domestication traits were obtained, providing candidate genes and a molecular marker for the molecular marker-assisted breeding research of domestication traits of largemouth bass.
Key words Micropterus salmoides     domestication traits    transcriptome sequencing    differentially expressed genes    single nucleotide polymorphism    

鱼类食性驯化是渔业养殖产业中的重要环节之一,尤其对于肉食性鱼类,驯化其摄食人工配合饲料与保护养殖水体环境、节约海洋资源、减少疾病发生等方面均密切相关。目前,对大熊猫(Ailuropoda melanoleuca)、狗(Canis lupus familiaris)、鲸(Cetacea)等哺乳动物食性驯化开展了较广泛的研究,解析了食性转变的分子机理[1-5],然而对鱼类食性驯化的分子调控机制研究相对匮乏。朱书礼等[6]发现鱼类胰α-淀粉酶基因5ʹ端序列的转录因子与鱼类食性转变具有一定的关系。鳜(Siniperca chuatsi)视黄醇脱氢酶8 (RDH8)、酪蛋白激酶(casein kinase, CK)、时钟基因(circadian locomoter output cycles protein kaput, CLOCK)、周期蛋白(PER)、神经肽(neuropeptide Y, NPY)、胆囊收缩素(cholecystokinin, CCK)、蛋白磷酸酶(protein phosphatase1, PP1)、突触结合蛋白(synaptotagmin, SYT)等基因可能是其易驯食人工饲料的重要调节因子[7-8]。在草鱼(Ctenopharyngodon idellus)的研究中发现胰岛素受体(insulin receptor, INSR)、葡糖激酶(glucokinase, GK)、丝氨酸蛋白酶(serine protease, PRSS)、周期蛋白(PER)、多巴胺受体D1 (dopamine receptor D1, DRD1)等基因可能与草鱼从食肉向食草转变相关[9]。此外,在鳜胃蛋白酶基因(pepsase, PEP)和生长激素基因(growth hormone, GH)、大口黑鲈脂蛋白脂酶基因(lipoprotein lipase, LPL)和长链脂酰辅酶A合成酶1基因(Acy-CoA synthetase long-chain family member 1, ACSL1)中均发现与驯食性状显著相关的SNP标记[10-13]。对肉食性鱼类进行人工配合饲料的驯化,通过人工定向选育易驯食人工配合饲料的优良品种,有助于肉食性鱼类的规模化养殖和经济效益提升。

大口黑鲈(Micropterus salmoides)属凶猛肉食性鱼类,原产于北美洲,20世纪80年代引入我国,经养殖推广,现已成为我国重要的淡水养殖经济鱼类。据渔业统计年鉴显示,2020年我国大口黑鲈养殖总产量为61.95万t[14]。本实验室以大口黑鲈“优鲈1号”和自美国引进的大口黑鲈野生群体为选育基础群体,以易驯化摄食配合饲料和生长性状为主要选育目标,经连续多代选育培育出大口黑鲈新品种“优鲈3号”,推动了大口黑鲈全人工配合饲料替代冰鲜幼杂鱼的养殖[15-16]。本研究以大口黑鲈“优鲈3号”为研究对象,根据接受人工配合饲料的难易程度分为易驯食组和不易驯食组,通过RNA-seq技术挖掘与食性驯化相关的通路及功能基因,进一步从这些基因中筛选与驯食性状关联的SNP位点,为利用分子标记技术辅助大口黑鲈食性驯化遗传改良奠定理论基础。

1 材料与方法 1.1 实验鱼及试验设计

实验鱼来自中国水产科学研究院珠江水产研究所广州基地。实验共设置3个平行组,每组分别放养5000尾出膜6 d的“优鲈3号”仔鱼于1500 L循环水养殖桶中,每天分别在7:00、9:00、12:00、14:00、16:00和18:00投喂丰年虫(购自天津丰年水产养殖有限公司),连续投喂14 d,在出膜后第20天开始进行驯化摄食人工配合饲料(购买自福建天马科技股份有限公司)。按照鱼苗对配合饲料的接受程度来判定是否驯化成功,在投喂饲料半个小时后,将腹部饱满的鱼苗定义为易驯食个体(腹部内容物/体重在18%~24%),反之则认为是不易驯食个体(腹部内容物/体重在8%~12%)[7]。在驯食第4天,从每个平行组中随机挑选易驯食和不易驯食个体各5尾,分别采集大脑和肝脏,并放入盛有RNA样品保存液的冻存管中4 ℃保存过夜后,再在−80 ℃条件下保存备用。

用于关联分析的群体是从每个平行组中随机选取不易驯食个体和易驯食个体各40尾,共计240尾,测量其全长和体重,同时剪取尾鳍样本放入装有无水乙醇的1.5 mL离心管中。按照海洋动物组织基因组DNA提取试剂盒[天根生化科技(北京)有限公司]说明书提取鳍条样品基因组DNA,利用1%琼脂糖(Sigma公司,美国)凝胶电泳和多功能酶标仪(BioTek公司,美国)对所获得的DNA样品进行质量和浓度的检测,置于−20 ℃保存备用。

1.2 RNA分离、文库制备和RNA测序

肝脏和脑组织总RNA的提取按照TRIzol试剂盒(Invitrogen,美国)说明书进行,用1%琼脂糖凝胶电泳和Nanodrop 2000超微量分光光度计(Thermo Scientific, Delaware,美国)检测RNA样品的完整性和浓度。每个平行组中易驯食组和不易驯食组的肝脏和脑组织各取1个RNA样本(每5尾鱼等质量混合提取一个RNA样本),共12个测序样本用于构建paired-end文库。用Ribo-zero试剂盒去除rRNA富集mRNA,然后加入破碎缓冲液将mRNA断化成短片段,再以短片段mRNA为模板,用六碱基随机引物合成cDNA第一链,并加入缓冲液、dNTPs、DNA 聚合酶I和RNase H合成cDNA第二链,用AMPure XP beads进行纯化,加“A”尾和测序接头,进行PCR扩增并用AMPure XP beads纯化PCR产物,得到最终的文库[17]。将构建好的文库用Illumina HiSeq 2000进行测序。

1.3 差异表达基因筛选

将测序原始序列用Trimmomatic软件[18]进行过滤得到clean reads。采用HISAT2[19]软件、Bowtie2[20]软件与本实验室大口黑鲈参考基因组(未发表)比对,进行基因注释,注释后的基因用FPKM[21]法计算基因表达量,用DEseq2[22]进行不同组间差异表达基因的筛选,筛选条件为FDR (false discovery rate)<0.05, |log2(FC)|>1。将筛选出的差异表达基因分别与NR数据库(ftp://ftp.ncbi. nlm.nih.gov/blast/db/)、GO数据库(http://www. geneontology.org)、KEGG数据库(http://www.genome. jp/kegg/)、Swiss-Prot数据库(http://web.expasy.org/ docs/swiss-prot_guideline.html)和KOG数据库(ftp://ftp.ncbi.nih.gov/pub/COG/KOG/kyva)进行BLASTx比对,注释差异表达基因,并进行GO功能分析和KEGG通路分析。为验证测序数据的可靠性,以用于转录组测序的RNA反转录成cDNA作为模板,对随机挑选的19个基因进行RT-PCR扩增,扩增体系为20 μL,包括10 μL SYBR Premix (TaKaRa, Dalian, China)、0.4 μL正反向引物、6.2 μL ddH2O以及3 μL (7.5倍稀释) cDNA模板。扩增条件为:95 ℃预变性2 min,然后95 ℃变性10 s, 60 ℃退火10 s, 72 ℃延伸10 s,循环40次,最后72 ℃延伸10 min。采用2–ΔΔCt法计算差异表达基因的相对表达水平。所有引物均委托广州艾基生物技术有限公司合成(表1)。

表1  RT-PCR引物序列 Tab. 1  RT-PCR primer sequence
1.4 SNP标记筛选及与驯食性状关联分析

为了筛查测序文库中单核苷酸多态性(single nucleotide polymorphism, SNP),采用GATK软件[23],将至少一个样本中reads丰度不小于4, QD<1, FS (FisherStrand)>30作为筛选条件,筛选出潜在SNP标记。为进一步验证转录组数据库中的SNP标记有效性,选择60尾易驯食个体和60尾不易驯食个体的DNA样品作为模板,挑选差异表达基因中的14个潜在SNP标记进行SNaPshot分型,最后在关联分析群体中进行标记与驯食性状的关联分析。SNaPshot分型检测委托上海捷瑞生物工程有限公司完成,首先是根据SNP标记上下游的序列设计引物,扩增含有SNP的目的片段,长度在200~500 bp。然后采用多重PCR扩增目的片段。PCR反应采用Touch-down方法,95 ℃预变性3 min; 94 ℃变性15 s, 60 ℃退火15 s, 72 ℃延伸30 s, 11个循环,每个循环的退火温度降0.5 ℃; 94 ℃变性15 s, 54 ℃退火15 s, 72 ℃延伸30 s, 24个循环;72 ℃延伸3 min。再将扩增到的目的片段用ExoI和FastAP进行纯化,去除反应产物中的剩余引物和dNTP。用SNaPshot试剂盒(ABI公司,美国)中的SNaPshot Mix试剂与纯化后的PCR产物混合,对PCR产物进行延伸反应,最后在ABI3730全自动测序仪上进行测序。

1.5 数据分析

采用SPSS26.0进行数据分析,用卡方检验进行SNP基因型与驯食性状的相关性分析,检验结果P<0.05表示显著相关。

2 结果与分析 2.1 转录组测序数据和基因注释

采用RNA-seq技术对大口黑鲈易驯食组和不易驯食组的肝脏和脑组织转录组进行分析,总共获得52234万条raw reads,过滤后得到51255万条高质量短读序(clean reads),共注释到27930个基因。各组Q30的碱基质量值比例均不小于93.00%,错误率均小于0.03% (表2)。此外,能成功比对到大口黑鲈参考基因组上的reads均超过91%,且有84%~87.81%的reads被比对到参考基因组的唯一位置,说明转录组测序数据可靠。

表2  大口鲈鱼肝脏、脑组织转录组文库测序数据 Tab. 2  Transcriptome library sequencing data of liver and brain in Micropterus salmoides
2.2 差异表达基因筛选

与不易驯食组相比,在易驯食组脑组织中有203个差异表达基因上调,159个差异表达基因下调;肝脏组织中有1778个差异表达基因上调,1611个差异表达基因下调。进一步对筛选到的差异表达基因进行GO功能性显著富集分析,脑和肝脏组织中差异表达基因分别富集到42和48个GO条目,其中脑组织中参与生物过程、分子功能和细胞组分相关联的基因个数占比分别为49.24%、20.15%和30.61%,肝脏组织中占比分别为49.75%、19.64%和30.61% (图1)。对差异表达基因进行KEGG通路分析,结果显示脑和肝脏组织中差异表达基因分别被富集到147和271个已知KEGG通路。将显著性富集(P<0.05)的前20条KEGG通路绘制成KEGG富集散点图(图2)。通过KEGG显著性富集确定差异表达基因参与的主要生化代谢途径和信号转导途径,包括昼夜节律通路、类固醇生物合成通路、PPAR信号通路、PI3K-AKT信号通路等。

图1  驯食组和不易驯食组大口黑鲈脑(a)和肝脏组织(b)中差异表达基因GO功能分类 Fig. 1  GO functional classification of differentially expressed genes in brain (a) and liver (b) tissues of domesticated and non-domesticated Micropterus salmoides groups
图2  驯食组和不易驯食组大口黑鲈脑(a)和肝脏组织(b)中差异表达基因KEGG富集散点图 Fig. 2  KEGG enrichment scatter plot of differentially expressed genes in brain (a) and liver (b) tissues of domesticated and non-domesticated Micropterus salmoides groups
2.3 食性驯化相关基因鉴定

对易驯食组和不易驯食组间的差异表达基因进行分析,发现与食性驯化相关基因主要参与昼夜节律、光传导、视黄醇代谢、类固醇生物合成、胆汁分泌和PI3K-AKT信号通路,这些通路调控环境适应、视觉系统、消化代谢、食欲控制等主要生物过程,包括LEPPERsRHORDHsBSEP等基因(图3)。其中,参与昼夜节律的PERs在易驯食组脑和肝脏组织中表达上调,CLOCK表达下调;参与光传导的RHO在易驯食组脑组织中表达下调;参与视黄醇代谢的RDHs在易驯食组肝脏组织中表达上调。涉及食欲控制和消化代谢的差异表达基因大多数在易驯食组肝脏组织中发生显著变化,在脑组织中未明显变化,例如参与食欲控制的LEP、胰岛素受体底物(insulin receptor substrate, IRS1)、丝氨酸/苏氨酸蛋白激酶(RAC serine/threonine-protein kinase, AKT)和参与消化代谢的BSEP、法尼基-二磷酸法尼基转移酶(farnesyl-diphosphate farnesyltransferase, FDFT1)在易驯食组肝脏组织中表达水平显著上调。为进一步验证转录组测序的准确性,从食性驯化相关基因中随机选择19个进行RT-PCR分析,结果显示19个基因的表达模式与测序结果一致(图4),表明测序结果的可信度高。

图3  不易驯食组和易驯食组大口黑鲈脑和肝脏组织中的差异表达基因与食性驯化相关的主要通路包括脑组织中昼夜节律通路(a)和光传导通路(b),肝脏组织中视黄醇代谢通路(c)、PI3K-AKT信号通路(d)、类固醇生物合成通路(e)、胆汁分泌通路(f). 红色表示相对于不易驯食组,易驯食组中差异表达基因显著上调;绿色表示相对于不易驯食组,易驯食组中差异表达基因显著下调(FDR<0.05, |log2(FC)|>1). Fig. 3  Differentially expressed genes in brain and liver tissues of domesticated and non-domesticated Micropterus salmoides groupsThe main pathways related to food domestication include circadian rhythm pathways (a) and phototransduction pathways (b) in brain; retinol metabolism pathways (c), PI3K-AKT signaling pathway (d), steroid biosynthesis pathways (e) and bile secretion pathways (f) in liver. Red indicates that differentially expressed genes are significantly up-regulated in domesticated group compared with non-domesticated group. Green indicates that differentially expressed genes are significantly down-regulated in domesticated group compared with non-domesticated group.
图4  不易驯食组和易驯食组大口黑鲈脑和肝脏组织中19个差异表达基因表达量分析 Fig. 4  Validation of the expression of 19 genes in brain and liver tissues of domesticated and non-domesticated Micropterus salmoides groups
2.4 SNP的筛选与分型

在不易驯食组和易驯食组中共筛选出111571个SNP位点,其中位于差异表达基因上的SNP位点有21465个。为进一步验证这些SNP位点的有效性,从差异表达基因中挑选出14个SNP位点进行分型检测。结果显示,14个SNP位点可成功分型(表3)。在验证群体中将14个SNP位点与驯食性状进行关联分析,筛选出4个与驯食性状存在潜在性相关的位点。进一步扩大群体进行关联分析,仅有1个SNP位点chr15-A+8322808G与驯食性状存在显著相关性(P<0.05)(表4)。该位点位于RDH12的3ʹUTR区域,存在3种基因型为AA、GG和AG (图5),其中AA基因型为易驯食群体中的优势基因型。

图5  chr15-A+8322808G标记基因型检测图a. AA基因型;b. GG基因型;c. AG基因型. Fig. 5  chr15-A+8322808G marker genotype detection mapa. AA genotype; b. GG genotype; c. AG genotype.
表3  差异表达基因中SNP位置及其基因注释 Tab. 3  SNP positions and their gene annotations in differentially expressed genes
表4  SNP位点的基因型频率及其与大口黑鲈驯食性状的关联分析 Tab. 4  Association analysis between genotype frequency of SNP and domestication traits in Micropterus salmoides
3 讨论

在自然条件下,动物的摄食行为具有一定规律,进而表现出类似昼夜节律的摄食模式,并最终形成一种类似“生物钟”的内源性节律[24-25]。昼夜节律是指生命活动以24 h左右为周期的变动,由正负反馈回路形成[26-27]。Cahill[24]发现斑马鱼(Danio rerio)昼夜节律形成的分子调控机制与哺乳动物基本一致,正反馈回路通过驱动CLOCK/ BMAL1异二聚体,从而激活下游含有E-box顺式增强子序列的靶基因转录,负反馈回路则是周期蛋白(PER1, PER2PER3)和隐花色素基因(cryptochrome, CRY1CRY2)的节律性转录[26]。PER和CRY蛋白形成异二聚体,作用于CLOCK/ BMAL1异二聚体,抑制其自身的转录[28]。Kobayashi等[29]通过禁食对小鼠(Mus culus)昼夜节律基因表达水平进行检测,发现禁食后PER2在肝脏中的表达水平显著降低。研究发现草鱼从食肉到食草和鳜从食活饵到食死饵的转变中,PERs基因在食性转变后表达水平下调,CLOCK基因表达水平上调[7,9]。本研究中易驯食组大口黑鲈PERs基因表达水平上调,CLOCK表达水平下调,说明生物钟基因表达水平的变化可能会改变其摄食的昼夜节律以适应驯化过程中食性转变。

视觉是过渡到外源性摄食和之后生存的基础,因为大多数鱼是视觉摄食者,故视觉是影响仔鱼开口摄食的主要因素之一[30]RHORDHs、鸟苷酸环化酶(guanylate cyclase, GC)是鱼类视觉系统的重要调节因子。光子将RHO中11-顺式视黄醛异构化为全反式视黄醛,并在暗视力和酶的作用下进一步被转化为11-顺式视黄醛,而后与视蛋白组合以完成视觉循环[31]。He等[32]发现视黄醇代谢是鳜从食活饵到配合饲料过程中重要的代谢途径。RDHs通过催化全反式视黄醛还原成全反式视黄醇(维生素A)进而影响鱼类的视觉、生长发育等生理功能[33-34]。Lucas等[35]研究发现鸟苷酸环化酶激活剂(guanylyl cyclase-activating protein, GCAP)作用的GC是催化cGMP合成的关键酶,而cGMP下降会导致光感受器外段质膜中阳离子通道关闭,从而影响视觉[36]。Liang等[37]和张瑞祺等[38]研究发现鳜难以进行饲料和死饵驯化的原因之一是其视力较弱,无法快速完成食物的识别,且拒食静止的食物,说明视觉能力在食性驯化过程中起重要作用。与不易驯化摄食人工配合饲料的鳜相比,易驯化鳜RDH8表达水平上调,GC表达水平下调[7]。本研究中易驯食组大口黑鲈肝脏组织中RDHs基因表达水平上调,GCAP表达水平下调,这一结果与鳜的研究结果相似。此外,易驯食组脑中RHO的转录水平显著高于不易驯食组,表明RHORDHsGCAP是大口黑鲈食性驯化中重要的视觉基因,进一步说明易驯食个体具有更好的视觉能力和光敏性。本研究在RDH12基因中鉴定到一个与驯食性状显著关联的SNP标记chr15-A+8322808G,该标记位于RDH12的3ʹUTR区域。SNP发生在基因非编码区可能会影响转录因子与DNA的结合、非编码RNA的序列、基因的剪接、mRNA的降解等,进而影响基因表达[39]RDH12基因位于光感受器内节段,其功能突变可能会导致先天性的视网膜退化[34,40]。故该SNP标记chr15-A+8322808G可能影响大口黑鲈视网膜的光敏性,进而影响食性驯化。因此认为,RDH12是影响大口黑鲈食性驯化的重要视觉基因。

食欲调控在食性驯化过程中起重要作用,动物的食欲调控是一个非常复杂的神经–外周调节过程,涉及外周食欲感受装置和中枢神经系统之间的一系列相互作用机制[41]。PI3K-AKT信号通路是食欲控制过程中重要的调控通路,与其他信号通路共同调控糖代谢、蛋白质合成等生物过程。其中,胰岛素结合细胞表面受体INSR通过IRS激活PI3K-AKT通路,IRS是胰岛素信号通路和代谢调控的关键下游分子[42]。在黄颡鱼(Pelteobagrus fulvidraco)肝脏中IRS2IRS1对胰岛素刺激更为敏感[43]。本研究中,IRS1在易驯食组肝脏组织中表达水平上调,而IRS2在易驯食组脑和肝脏中表达水平下调,说明IRS基因在食性驯化过程中起重要作用。AKT基因作为PI3K-AKT信号通路中重要的调控因子,通过抑制糖原合成酶激酶3β (glycogen synthase kinase-3β, GSK3β)磷酸化,进而激活糖原合成酶(glycogen synthase, GYS)导致糖原的合成,降低血糖[44]GSK3β对胰岛素信号通路有负反馈作用[45]。本研究中AKTGSK3βGYS基因在易驯食组肝脏组织中表达水平上调,进一步说明PI3K-AKT信号通路是参与大口黑鲈食性驯化的重要食欲控制通路。此外,瘦素是食欲控制中重要的外周食欲调控激素。LEP在摄食行为和能量消耗方面起着重要作用[46-47]。在草鱼食性转变研究中发现肝脏组织中LEP表达水平显著增加[9],在饱腹组刀鲚(Coilia nasus)的胃组织中LEP表达水平也显著增强[48]。与不易驯食组相比,本研究中易驯食组肝脏组织中LEP表达量显著增加(P<0.05),说明LEP作为一个饱腹信号来调控食欲,进而参与食性驯化过程。

消化代谢是影响鱼类食物摄入的主要因素之一。食物的消化代谢可为机体提供维持正常生命活动所需的物质和能量[49]。结果显示,易驯食组与不易驯食组肝脏组织中存在大量与消化代谢相关的差异表达基因,包括参与胆汁分泌[50]的羟甲基戊二酰辅酶A还原酶(3-hydroxy-3-methylglutaryl- coenzyme A reductase, HMGCR)、BSEP;参与类固醇生物合成[51]FDFT1、角鲨烯单加氧酶(squalene monooxygenase, SQLE);参与蛋白质消化吸收[52-53]的肽酶(neprilysin, CD10)和胶原蛋白(collagen, COL);参与胰腺分泌[54]的鸟苷酸结合蛋白(guanine nucleotide-binding protein, GNAQ)、Ras相关蛋白(ras-related protein, RABs, RAP1);参与脂肪酸消化吸收[55]的二酰基甘油转移酶(diacylglycerol O-acyltransferase, DGAT)、微粒体甘油三酯转运蛋白(microsomal triglyceride transfer protein, MTTP)和载脂蛋白(apolipoprotein B, APOB)。其中类固醇生物合成是KEGG通路中富集显著的通路,SQLEFDFT1是类固醇生物合成中关键酶,可调控胆固醇、油菜素甾醇、麦角固醇的生成以及促进初级胆汁酸和类固醇激素的生物合成。胆汁分泌是影响消化代谢重要的生物过程,其中胆汁酸(BAs)有助于脂肪吸收,在葡萄糖和代谢调节中发挥作用[50]。本研究中BSEP基因在易驯食肝脏组织中表达水平显著上调(P<0.01), BSEP介导的胆汁酸流出是胆汁分泌的主要驱动力,而胆汁是小肠消化和吸收脂肪和脂溶性维生素所必需的,进而影响食物摄入[56-57]。参与消化代谢的差异表达基因在易驯食组肝脏中表达水平显著上调,说明易驯食组个体对配合饲料的消化代谢能力更强,进一步解释了易驯食组对人工配合饲料接受程度高的原因。

综上所述,本研究利用RNA-seq技术对大口黑鲈易驯食组和不易驯食组的脑和肝脏组织进行转录组测序分析,分别筛选到362和3389个差异表达基因,并从这些差异表达基因中检测到21465个SNP位点。影响大口黑鲈食性驯化的差异表达基因主要参与昼夜节律、光传导、视黄醇代谢、类固醇生物合成、胆汁分泌和PI3K-AKT信号通路,这些通路调控环境适应、视觉系统、消化代谢、食欲控制等主要生物过程,包括LEPPERsRHORDHsBSEP等基因。RDH12基因中chr15-A+8322808G突变位点与驯食性状显著关联(P<0.05),其AA基因型为易驯食个体中的优势基因型。本研究获得了与大口黑鲈驯食性状相关的64个候选基因和1个SNP标记,为大口黑鲈食性驯化性状的分子标记辅助育种研究提供了候选基因和分子标记,也为肉食性鱼类食性遗传改良提供理论基础和依据。

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