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Comparative chromosome mapping of 45S rDNA in four species of abalone

  • Corresponding author: Mingyi CAI, myicai@jmu.edu.cn
  • Received Date: 2018-12-20
    Accepted Date: 2019-04-01
  • Abalone is not only precious seafood in China, but also important mariculture shellfish. In recent years, the genetic breeding research of abalone has made rapid progress, but the research data of cytogenetic analysis is still in lack. Therefore, this study used the fluorescence in situ hybridization (FISH) to compare the distribution of 45S rDNA clusters in Haliotis discus hannai, H. gigantea, H. fulgens, and H. diversicolor. In H. discus hannai, 83% of the metaphase had 2 pairs of 45S rDNA sites, locating at terminal of the long arm ends of chromosomes 13th and 16th, respectively. In H. gigantea, about 75% of the metaphase had 3 pairs of 45S rDNA sites, locating at the terminal of the short arm of chromosome 6th, and at the terminal of the long arm of chromosomes 14th and 17th, respectively. In H. fulgens, about 85% of the metaphase cells detected three pairs of 45S rDNA sites located at the terminal of the long arms of chromosomes 4th, 6th, and 8th. In H. diversicolor, about 65% of the metaphase had 3 pairs of 45S rDNA sites, locating at the terminal of the short arms of chromosomes 3th, 4th, and 12th. In addition to the main mode, there were other low-frequency modes in all the 4 species of abalone, suggesting that these abalone may have several unstable 45S rDNA sites besides the unambiguous sites. The number and the location of 45S rDNA loci in abalone showed a high level of intraspecific variation in general. These findings enrich the cytogenetic research data of abalone and provide basic data for the further studies of genetic breeding in abalone.
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  • [1] Franchini P, Slabbert R, Van Der Merwe M, et al. Karyotype and genome size estimation of Haliotis midae: Estimators to assist future studies on the evolutionary history of haliotidae[J]. Journal of Shellfish Research, 2010, 29(4): 945-950. doi: 10.2983/035.029.0428
    [2] 郭战胜, 侯旭光. 鲍科染色体研究进展[J]. 水产科学, 2016, 35(5): 597-602.Guo Z S, Hou X G. Research progress on chromosome in family haliotidae[J]. Fisheries Science, 2016, 35(5): 597-602(in Chinese).
    [3] 蔡明夷, 刘贤德, 陈紫瑩, 等. 皱纹盘鲍染色体C带和rDNA定位[J]. 水产学报, 2013, 37(7): 1002-1008.Cai M Y, Liu X D, Chen Z Y, et al. Characterization of Pacific abalone (Haliotis discus hannai) karyotype by C-banding and fluorescence in situ hybridization with rDNA[J]. Journal of Fisheries of China, 2013, 37(7): 1002-1008(in Chinese).
    [4] Cai M Y, Ke C H, Luo X, et al. Karyological studies of the hybrid larvae of Haliotis disversicolor supertexta female and Haliotis discus discus male[J]. Journal of Shellfish Research, 2010, 29(3): 735-741. doi: 10.2983/035.029.0327
    [5] 权洁霞, 戴继勋. 荧光原位杂交技术(FISH)在鱼类遗传学研究中的应用及前景[J]. 动物学研究, 1999, 20(3): 225-229. doi: 10.3321/j.issn:0254-5853.1999.03.012Quan J X, Dai J X. Current and future application of fluorescence in situ hybridization (FISH) techniques to FISH genetics: a review[J]. Zoological Research, 1999, 20(3): 225-229(in Chinese). doi: 10.3321/j.issn:0254-5853.1999.03.012
    [6] Gallardo-Escárate C, Álvarez-Borrego J, Del Río-Portilla M A, et al. Karyotype analysis and chromosomal localization by FISH of ribosomal DNA, telomeric (TTAGGG)n and (GATA)n repeats in Haliotis fulgens and H. corrugata (Archeogastropoda: Haliotidae)[J]. Journal of Shellfish Research, 2005, 24(4): 1153-1160. doi: 10.2983/0730-8000(2005)24[1153:KAACLB]2.0.CO;2
    [7] Hernández-Ibarra N K, Ibarra A M, Cruz P, et al. FISH mapping of 5S rRNA genes in chromosomes of North American abalone species, Haliotis rufescens and H. fulgens[J]. Aquaculture, 2007, 272(Suppl 1): S268. doi: 10.1016/j.aquaculture.2007.07.086
    [8] Gallardo-Escárate C, Álvarez-Borrego J, Ángel Del Río-Portilla M, et al. Fluorescence in situ hybridization of rDNA, telomeric (TTAGGG)n and (GATA)n repeats in the red abalone Haliotis rufescens (Archaeogastropoda: Haliotidae)[J]. Hereditas, 2005, 142(2005): 73-79. doi: 10.1111/j.1601-5223.2005.01909.x
    [9] 王海山. 三种鲍种间杂交的细胞遗传学研究[D]. 厦门: 厦门大学, 2014.Wang H S. Cytogenetic characterization of interspecies hybrids in three species of abalone[D]. Xiamen: Xiamen University, 2014 (in Chinese).
    [10] 刘圆圆. 杂色鲍与皱纹盘鲍及其杂交子代的分子细胞遗传学研究[D]. 厦门: 厦门大学, 2016.Liu Y Y. Molecular Cytogenetic Studies on Haliotis diversicolor diversicolor, H. discus hannai and the interspecific hybrid[D]. Xiamen: Xiamen University, 2016 (in Chinese).
    [11] Arai K, Tsubaki H, Ishitani Y, et al. Chromosomes of Haliotis discus hannai INO and H. Discus REEVE[J]. Nippon Suisan Gakkaishi, 1982, 48(12): 1689-1692. doi: 10.2331/suisan.48.1689
    [12] 杨文杰, 黄勃, 王仁恩, 等. 海南不同地理群体羊鲍18S rDNA的克隆与序列分析[J]. 安徽农业科学, 2012, 40(20): 10370-10373. doi: 10.3969/j.issn.0517-6611.2012.20.005Yang W J, Huang B, Wang R E, et al. Cloning and sequence analysis of Haliotis ovina 18S rDNA in the different geographical populations of Hainan[J]. Journal of Anhui Agricultural Sciences, 2012, 40(20): 10370-10373(in Chinese). doi: 10.3969/j.issn.0517-6611.2012.20.005
    [13] Levan A, Fredga K, Sandberg A A. Nomenclature for centromeric position on chromosomes[J]. Hereditas, 1964, 52(2): 201-220. doi: 10.1111/j.1601-5223.1964.tb01953.x
    [14] Martins C, Wasko A P. Organization and evolution of 5S ribosomal DNA in the fish genome[M]//Williams C R. Focus on Genome Research. New York: Nova Science Publishers, 2004: 335-363.
    [15] Gornung E. Twenty years of physical mapping of major ribosomal RNA genes across the teleosts: a review of research[J]. Cytogenetic and Genome Research, 2013, 141(2-3): 90-102. doi: 10.1159/000354832
    [16] Yano C F, Poltronieri J, Bertollo L A C, et al. Chromosomal mapping of repetitive DNAs in Triportheus trifurcatus (Characidae, Characiformes): Insights into the differentiation of the Z and W chromosomes[J]. PLoS One, 2014, 9(3): e90946. doi: 10.1371/journal.pone.0090946
    [17] Wang H S, Luo X, You W W, et al. Cytogenetic analysis and chromosomal characteristics of the polymorphic 18S rDNA of Haliotis discus hannai from Fujian, China[J]. PLoS One, 2015, 10(2): e0113816. doi: 10.1371/journal.pone.0113816
    [18] 朱齐春, 郑娇, 张静, 等. 眼斑拟石首鱼重复DNA序列的染色体定位[J]. 水生生物学报, 2017, 41(6): 1218-1224. doi: 10.7541/2017.151Zhu Q C, Zheng J, Zhang J, et al. Location of repetitive DNA sequences on the chromosome of sciaenops ocellatus[J]. Acta Hydrobiologica Sinica, 2017, 41(6): 1218-1224(in Chinese). doi: 10.7541/2017.151
    [19] Sochorová J, Garcia S, Gálvez F, et al. Evolutionary trends in animal ribosomal DNA loci: introduction to a new online database[J]. Chromosoma, 2018, 127(1): 141-150. doi: 10.1007/s00412-017-0651-8
    [20] Gromicho M, Coelho M M, Alves M J, et al. Cytogenetic analysis of Anaecypris hispanica and its relationship with the paternal ancestor of the diploid-polyploid Squalius alburnoides complex[J]. Genome, 2006, 49(12): 1621-1628. doi: 10.1139/g06-121
    [21] Książczyk T, Taciak M, Zwierzykowski Z. Variability of ribosomal DNA sites in Festuca pratensis, Lolium perenne, and their intergeneric hybrids, revealed by FISH and GISH[J]. Journal of Applied Genetics, 2010, 51(4): 449-460. doi: 10.1007/BF03208874
    [22] Cazaux B, Catalan J, Veyrunes F, et al. Are ribosomal DNA clusters rearrangement hotspots? A case study in the genus Mus (Rodentia, Muridae)[J]. BMC Evolutionary Biology, 2011, 11: 124. doi: 10.1186/1471-2148-11-124
    [23] Symonová R, Majtánová Z, Sember A, et al. Genome differentiation in a species pair of coregonine fishes: An extremely rapid speciation driven by stress-activated retrotransposons mediating extensive ribosomal DNA multiplications[J]. BMC Evolutionary Biology, 2013, 13: 42. doi: 10.1186/1471-2148-13-42
    [24] Leighton D L, Lewis C A. Experimental hybridization in abalones[J]. International Journal of Invertebrate Reproduction, 1982, 5(5): 273-282. doi: 10.1080/01651269.1982.10553479
    [25] Roa F, Guerra M. Distribution of 45S rDNA sites in chromosomes of plants: structural and evolutionary implications[J]. BMC Evolutionary Biology, 2012, 12: 225. doi: 10.1186/1471-2148-12-225
    [26] Kovarik A, Dadejova M, Lim Y K, et al. Evolution of rDNA in Nicotiana allopolyploids: a potential link between rDNA homogenization and epigenetics[J]. Annals of Botany, 2008, 101(6): 815-823. doi: 10.1093/aob/mcn019
    [27] Pedrosa-Harand A, De Almeida C C S, Mosiolek M, et al. Extensive ribosomal DNA amplification during Andean common bean (Phaseolus vulgaris L.) evolution[J]. Theoretical and Applied Genetics, 2006, 112(5): 924-933. doi: 10.1007/s00122-005-0196-8
    [28] Pich U, Fuchs J, Schubert I. How do Alliaceae stabilize their chromosome ends in the absence of TTTAGGG sequences?[J]. Chromosome Research, 1996, 4(3): 207-213. doi: 10.1007/BF02254961.
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Comparative chromosome mapping of 45S rDNA in four species of abalone

    Corresponding author: Mingyi CAI, myicai@jmu.edu.cn
  • 1. Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture and Rural Affairs, Fisheries College, Jimei University, Xiamen 361021, China
  • 2. Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China

Abstract: Abalone is not only precious seafood in China, but also important mariculture shellfish. In recent years, the genetic breeding research of abalone has made rapid progress, but the research data of cytogenetic analysis is still in lack. Therefore, this study used the fluorescence in situ hybridization (FISH) to compare the distribution of 45S rDNA clusters in Haliotis discus hannai, H. gigantea, H. fulgens, and H. diversicolor. In H. discus hannai, 83% of the metaphase had 2 pairs of 45S rDNA sites, locating at terminal of the long arm ends of chromosomes 13th and 16th, respectively. In H. gigantea, about 75% of the metaphase had 3 pairs of 45S rDNA sites, locating at the terminal of the short arm of chromosome 6th, and at the terminal of the long arm of chromosomes 14th and 17th, respectively. In H. fulgens, about 85% of the metaphase cells detected three pairs of 45S rDNA sites located at the terminal of the long arms of chromosomes 4th, 6th, and 8th. In H. diversicolor, about 65% of the metaphase had 3 pairs of 45S rDNA sites, locating at the terminal of the short arms of chromosomes 3th, 4th, and 12th. In addition to the main mode, there were other low-frequency modes in all the 4 species of abalone, suggesting that these abalone may have several unstable 45S rDNA sites besides the unambiguous sites. The number and the location of 45S rDNA loci in abalone showed a high level of intraspecific variation in general. These findings enrich the cytogenetic research data of abalone and provide basic data for the further studies of genetic breeding in abalone.

  • 鲍(Haliotis ),在分类学上隶属于软体动物门(Mollusca)、腹足纲(Gastropoda)、前鳃亚纲(Prosobranchia)、原始腹足目(Archaeogastropoda)、鲍科(Haliotidae),是我国传统的海珍品。迄今为止,全世界已发现的现存种类有近百种,已命名的约56种[1],已查明染色体核型的鲍约17种[2]。现有的核型数据显示,鲍属的染色体数目与其地理分布具有明显相关性,地中海地区的鲍种染色体数目为2n=28;印度-太平洋亚洲地区鲍种染色体数目为2n=32;北太平地区鲍种、南非-澳大利亚鲍种染色体数目均为2n=36[3]。可见,染色体数目可能在鲍属的物种发生与进化中具有重要作用[4]。然而,目前鲍属的染色体研究主要局限于核型分析,以及少量带型与重复序列FISH定位等方面[4]

    荧光原位杂交(fluorescence in situ hybridization,FISH)是一种将分子生物学方法与细胞遗传学方法相整合的技术[5],近30年内得到了长足发展,为精细研究贝类染色体形态、结构提供了有力工具。鲍染色体的FISH研究尚处于起步阶段,研究资料匮乏,导致关于鲍属染色体进化机制研究进程较慢,及无法支持鲍遗传育种研究的迅速发展[6-10]。因而,本研究利用FISH比较定位了我国4种重要的养殖鲍类—皱纹盘鲍(H. discus hannai)、西氏鲍(H. gigantea)、绿鲍(H. fulgens)和杂色鲍(H. diversicolor)的45S rDNA,为深入研究鲍的染色体进化与遗传育种提供必要的基础数据。

1.   材料与方法
  • 皱纹盘鲍主要分布于太平洋西北区[1],实验用亲鲍为引自我国东北外海的底播养殖群体的多代繁殖后代;西氏鲍主要分布于太平洋西北区[1],实验用亲鲍为引自日本野生群体的多代繁殖后代;绿鲍主要分布于主要分布于太平洋东北区[1],实验用亲鲍为引自美国野生群体的多代繁殖后代;杂色鲍主要分布于印度洋-太平洋亚洲区[1],实验用亲鲍为捕自台湾海峡的多代繁殖后代。以上亲鲍均由中国福建晋江福大鲍鱼水产有限公司提供。

    采用经紫外线照射的水刺激亲鲍催产,精卵按一定比例混合进行人工授精。受精卵在室温下孵育,采用300目筛绢网收集孵化出的担轮幼虫。同时取鲍肌肉于无水乙醇中固定,备用。

  • 取鲍成体肌肉约30 mg,使用DNA提取试剂盒(上海捷瑞生物工程有限公司)提取鲍全基因组DNA。按Arai等[11]的方法制备鲍染色体。

  • 实验以45S rDNA部分序列(18S rDNA编码区的一个保守区段)为模板制备探针。这一区段序列通过PCR获得,引物为贝类18S rDNA通用引物18F(5′-AACCTGGTTGATCCTGCCAGT-3′)、18R(5′-TGATCCTTCTGCAGGTTCA-3′)[12]。扩增产物采用缺口平移法标记上生物素,具体操作参照试剂盒说明书(罗氏集团股份有限公司)。

  • 将已知浓度的探针加入到35 μL 杂交缓冲液(50% 硫酸葡聚糖、去离子甲酰胺、20×SSC缓冲液)中,使探针终浓度约为2 ng/μL。将混合液置于72 °C水浴锅中变性8 min,然后置于冰上10 min以上。

  • 74 °C水浴加热变性缓冲液(去离子甲酰胺、20×SSC缓冲液、蒸馏水)约5 min,将经老化的染色体载玻片置于变性缓冲液中处理2~3 min,经变性的染色体载玻片分别在梯度乙醇溶液(70%、80%、90%、100% 和100%)中各脱水30 s,最后将脱水后的玻片风干。

  • 在风干后的玻片样本位置上滴加经变性的探针杂交混合液,均匀平整的盖上封口膜后置于装有少量2×SSC缓冲液的湿盒内,于37 °C(恒温箱或杂交炉)杂交过夜(12~16 h)。

  • 揭去封口膜,将杂交后的玻片依次置于洗脱缓冲液(去离子甲酰胺、20×SSC缓冲液、蒸馏水)(37 °C)、4×SSC缓冲液(室温)、4×SSC缓冲液(室温)中各处理5 min,以便洗脱未杂交成功的残余探针。甩去玻片表面液体,将100 μL探针的一抗溶液(Avidin- Alexa Fluor 488溶液)滴加在样品上,盖上封口膜放于湿盒中,于37 °C恒温箱中温育30 min。黑暗条件下揭掉载玻片上的封口膜,将玻片依次置于室温下的4×SSC-Triton溶液、4×SSC缓冲液、4×SSC缓冲液中各洗涤5 min。最后用双蒸水轻轻冲洗,置于避光处风干。

  • 用10 μL的PI负染10 min,使用Olympus BX53荧光显微镜完成观察与拍照。通过相应荧光滤片组观察FISH荧光信号。用带有DP73电荷耦合器件图像传感器(CCD)拍摄图像,使用CellSens图像采集系统采集图像,并进行图像的多通道组合及初步处理,后期再用Image-pro plus 6.0生物学图像分析软件进行精确的染色体核型结构与信号位点等的分析与测量。参照Levan 等[13]提出的分组标准进行染色体分类,同一类染色体按相对长度递减顺序排列。

2.   结果
  • 利用FISH技术定位皱纹盘鲍、西氏鲍、绿鲍和杂色鲍中期染色体上45S rDNA的位置,染色体被碘化丙啶(PI)染为红色,45S rDNA位点呈现黄绿色荧光信号。每个物种取100个中期细胞进行观察、计数,并获得45S rDNA 基因簇数目直方图。其中,西氏鲍、绿鲍和杂色鲍等3种鲍的45S rDNA 基因簇数目的众数均为3对,而皱纹盘鲍为2对(图1)。

    Figure 1.  Histogram of 45S rDNA loci in 4 species of abalone

    取染色体数目和45S rDNA位点数都与其众数相符的中期相细胞进行核型分析(图版Ⅰ)。皱纹盘鲍核型公式为2 n=36=20 m+16 sm,约83%的中期细胞检出2对45S rDNA位点,分别位于13号染色体(亚中部着丝粒染色体,sm)长臂和15号染色体(sm)长臂的端部(图版Ⅰ-12)。西氏鲍的核型也为2 n=36=20 m+16 sm,约75 %的中期细胞检出3对45S rDNA位点,其中2对位于14号染色体(sm)长臂和17号染色体(sm)长臂的端部,1对位于5号染色体(中部着丝粒染色体,m)短臂端部(图版Ⅰ-34)。绿鲍的核型公式为2 n=36=16 m+16 sm+4 st,约85%的中期细胞检出3对45S rDNA位点,全部位于m染色体(4号、6号和8号)长臂的端部(图版Ⅰ-56)。杂色鲍的核型公式为2 n=32=16 m+14 sm+2 st,约69%的中期细胞检出3对45S rDNA位点,其中2对位于m染色体(3号和4号)短臂端部,1对位于sm染色体(12号)短臂端部(图版Ⅰ-78)。除了主要模式外,4种鲍的45S rDNA信号还有其他出现频率较低的分布方式(图版Ⅱ)。

    Figure 图版Ⅰ.  FISH mapping of 45S rDNA and karyotype of 4 species of abalone

    Figure 图版Ⅱ.  Other patterns of 45S rDNA loci in 4 species of abalone

3.   讨论
  • 染色体核型指的是染色体组在有丝分裂中期的表型,包括染色体数目、大小、形态特征[4]。在本研究中,4种鲍核型均符合前人报道[4],所有种类均含有中部着丝粒染色体和亚中部着丝粒染色体,绿鲍和杂色鲍还含有亚端部着丝粒染色体。虽然关于这4种鲍的核型已有多篇报道,但是不同的报道结果之间略有不同[4]。同一物种的染色体核型多态的现象在贝类中较为常见[4],此现象原因可能包括两方面:染色体制备方法可能会影响染色体的形态;低等动物种群内或种群之间由于染色体变异而导致染色体多态。由于这些不确定因素的存在,我们需要开发更多的染色体标记提高这4种鲍的染色体辨识度。

    真核生物中,45S rDNA基因是编码核糖体RNA的串联重复序列,由18S、5.8S和28S rDNA组成。45S rDNA通常在基因组中成簇排列[14]。45S rDNA编码序列在种间具有极高的保守性,且不同重复单元序列高度一致,是研究重复序列分子进化机制的模型[15]。在细胞遗传学研究中,45S rDNA位点研究也是最多的细胞遗传标记,在一些物种中还可能与性别决定区域相关联[16]。45S rDNA的染色体分布可以通过银染、CMA染色或DAPI染色等方法来显示,更直接的方法是以45S rDNA或其中部分序列(如18S rDNA)为探针用作FISH定位[17]

    目前,已利用FISH定位45S rDNA(或18S rDNA)的鲍共6种(表1),结果发现,鲍类45S rDNA位点的数目和位置普遍存在较大的种内变化。以皱纹盘鲍为例,现有的3篇报道结果互不相同。蔡明夷等[3]以2个质粒(含人类的18S rDNA、5.8S rDNA、28S rDNA和一段7.3 kb间隔序列片段)制备杂交探针作FISH,共检出4对阳性信号。Wang等[17]以PCR扩增18S rDNA部分编码区制备杂交探针作FISH,发现81%的细胞具有2对信号,分别位于14号和17号染色体长臂端部;同时,还存在着其他低频率位点分布模式,表现出较高的种内多态性。本实验中,皱纹盘鲍45S rDNA位点染色体定位结果与Wang[3]的结果相近,也检出2对阳性信号,少于蔡明夷等[3]所报道的4对阳性信号。造成这些结果差异的主要原因可能是,蔡明夷等[3]用以制备探针的DNA片段较长,因而检出的灵敏度相应较高。综合现有研究结果可以推测,皱纹盘鲍至少存在2对大的45S rDNA位点,FISH信号稳定;同时可能还存在若干对小的45S rDNA位点,FISH信号不稳定。Gallardo-Escárate等[6, 8]在红鲍、绿鲍和粉红鲍中观察得到同样的结果,3种鲍的中期染色体中均有2对信号明确的和若干对不稳定的45S rDNA信号。在现有动物细胞遗传学研究资料中,约有12%的物种表现出rDNA数目和分布位置的种内变化[19]。基因组中,低于FISH检测灵敏度下限的rDNA位点的扩增,或者失去活性的rDNA逐渐被排除,可能是导致rDNA位点数目和位置多态的重要原因。此外,不同实验室FISH程序的检测灵敏度差异也可能导致45S rDNA定位发生变动。

    种类 species核型 karyotype45S rDNA(or 18S rDNA)文献 reference
    对数 pair位置 location
    皱纹盘鲍 H. discus hannai 14 m+6 m/sm+16 sm 4 2 th, TER;7 th, TER;12 th, TER;18 th, TER [3]
    20 m+16 sm 2 14 th, TER;17 th, TER [17]
    20 m+16 sm 2 13 th, TER;15 th, TER 本研究
    西氏鲍 H.gigantea 20 m+16 sm 3 9 th, TER;12 th, TER;14 th, TER [9]
    20 m+16 sm 3 5 th, TER;14 th, TER;17 th, TER 本研究
    绿鲍 H. flugens 16 m+16 sm+4 st 2 4 th, TER;11 th, TER [6]
    16 m+16 sm+4 st 3 4 th, TER;6 th, TER;8 th, TER 本研究
    红鲍 H. rufescens 16 m+18 sm+2 st 2 4 th, TER;5 th, TER [8]
    粉红鲍 H. corrugata 20 m+14 sm+2 st 2 2 nd, TER;4 th, TER [6]
    杂色鲍 H. deiversicolor 16 m+14 sm+2 t 3 3 rd, TER;4 th, TER;12 th, TER 本研究
    注: 相对位置参考朱齐春(2017) [18]; TER=端部着丝粒染色体着丝粒末端或者亚端部着丝粒染色体的短臂端部
    Notes: the relative locations refer to the Zhu (2017) [18]; TER=centromeric termini of acrocentric chromosomes or terminal on the p-arms

    Table 1.  Summary of location of 45S rDNA in abalone

    目前已报道的动物核型中,约60%具有单对45S rDNA位点,但几乎在所有类群中都存在多对位点的核型[19]。贝类核型中,45S rDNA位点的众数为1对,平均数为3.18对[19]。鲍一般具有2~3对明确的45S rDNA位点和若干对不稳定的小位点,为多对位点模式(表1)。目前认为,多倍化[20]、种间杂交[21]、非同源位点间重组[22]、转座子的作用[23]等原因可能导致45 rDNA位点数目增多。自然状态下,鲍易发生种间杂交,而且杂交子代常获得明显的杂种优势[24]。Cai等[4]在分析杂色鲍×皱纹盘鲍杂交子代核型时发现,杂交F1复合染色体组很不稳定[4]。杂种染色体组不稳定是导致rDNA位点获得或丢失的重要原因[21]。然而,在鲍属中究竟是什么原因导致其45S rDNA位点数目普遍高于贝类45 rDNA位点的众数,以及45S rDNA位点的扩张的生物学意义是什么?解答这些问题尚需更多的研究数据。

    虽然鲍45S rDNA的位点数目扑朔迷离,但其染色体分布区域非常稳定,全部信号均分布于染色体端部(表1)。真核生物中,45S rDNA位点分布于染色体端部是主流模式。Roa等[25]和Gornung[15]分别综述了植物和鱼类45S rDNA定位研究资料,研究表明,超过50%的被子植物和约43%的鱼类具有染色体端部分布的45S rDNA位点。Sochorová等[19]统计了54种贝类的45S rDNA定位结果,发现67%的位点为染色体端部分布[19]。研究人员认为,rDNA分布于染色体端部利于其发生同源重组,而同源重组可能是rDNA协同进化的重要维持机制[26];染色体端部分布也便于rDNA位点在染色体间扩增与重排[27];此外,端部分布串联重复rDNA可能还具有保护染色体的作用,与端粒作用类似[28]

    综上所述,皱纹盘鲍、西氏鲍、绿鲍和杂色鲍等4种鲍均具有多对45S rDNA位点,其中2~3对位点信号明确,全部位于染色体端部。鲍的45S rDNA位点的数目和分布位置普遍表现出较高水平的种内变化,位点数目与物种的地理分布之间未发现明显的相关性。与鲍的经济价值及其遗传育种研究的发展状况相比,现有鲍的细胞遗传学研究水平明显落后。在进行鲍染色体进化研究、以及杂交育种和多倍体育种,有必要开展更多的分子细胞遗传学研究。

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