470 million years of conservation of microsatellite loci among fish species
470 million years of conservation of microsatellite loci among fish species
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DOI：
10.1098/rspb.1996.0083
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发表时间：
1996-05-22
影响因子：
4.7
通讯作者：
Hewitt, G
中科院分区：
文献类型：
--
作者：
Rico, C;Rico, I;Hewitt, G
用18个微卫星基因座对不同鱼种(代表鱼类的三个主要超纲和最主要的超目)的18个微卫星座位进行了检测，以检验在远缘类群中微卫星区域的保守性。研究采用了三种方法。首先，利用相关的微卫星基序探针对扩增片段进行Southern印迹分析。共有17对被测引物在至少4种被测物种中产生了预期大小范围内的产物。其次，对两个研究位点的扩增产物在五种鱼类中进行克隆和测序，发现其侧翼和微卫星序列具有高度的保守性。最后，在非来源物种中成功扩增的17个基因座在9个物种的无关个体群体中进行了多态测试，在几个案例中显示了广泛的多态。基因座起源的物种或关系密切的物种的多态水平普遍较高。在测试物种(4.7亿年)的鱼类进化过程中，特定微卫星基序的侧翼序列的保守性远远超过迄今报道的水平，并支持(源自对鲸鱼和海龟的研究)关于水生生物核和线粒体序列中碱基替换率低于陆地生物的建议。另一种解释是，尽管这些序列通常被认为是中性的，但它们可能在真核基因组中发挥重要作用，并可能受到强烈的选择性限制。这项研究表明，异源引物将成为鱼类物种间多态标记的现成来源，但也表明在跨物种可变性比较中应谨慎使用。
Primers for 18 microsatellite loci originally isolated from whiting (Merlangius merlangus, n = 6), stickleback (Gasterosteus aculeatus, n = 5) and cod (Gadus morhua, n = 7) were tested across a panel of diverse fish species, representing the three principal superclasses and most principal superorders of fish, to examine conservation of microsatellite regions across distantly related taxa. Three methods were used. First, amplified fragments were analysed by Southern blotting using the relevant microsatellite motif probes. A total of 17 of the tested primer pairs gave a product in the expected size range in at least four of Il tested species. Second, for two study loci the amplified polymerase chain reaction products were cloned and sequenced in five fish species to reveal a high level of conservation of the flanking and microsatellite sequences. Finally, the 17 loci successfully amplified in non-source species were tested for polymorphism in groups of unrelated individuals from nine species, in several cases revealing extensive polymorphism. Levels of polymorphism were generally high in species from which the loci were derived or among closely related species. The conservation of flanking sequences for particular microsatellite motifs over the span of fish evolution represented in the test species (470 million years) far exceeds that hitherto reported and lends support to the suggestion (derived from studies of whales and marine turtles) that the rate of base substitution in nuclear and mitochondrial sequences is lower in aquatic than terrestrial organisms. A further explanation could be that these sequences, although generally considered neutral, may play an important role in eukaryotic genomes, and may be under strong selective constraints. The study suggests that heterologous primers will be a ready source of polymorphic markers among fish species, but also indicates that caution should be used in cross-species comparisons of variability.