鳞翅目昆虫基因组中微卫星DNA的特征以及对其分离的影响

本文根据我们对鳞翅目昆虫棉铃虫和松毛虫以及其它动物 (筏蜘蛛、朱、鳕鱼和飞蝗 )的微卫星富集性基因组DNA文库的筛选和分析结果 ,结合其它实验室已发表的资料 ,对鳞翅目昆虫基因组中微卫星DNA的丰度和结构特点进行了较为系统的分析。结果表明 :与其它类群相比 ,尽管鳞翅目昆虫物种间存在差异 ,但其基因组中存在明显偏多的侧翼序列重复的、以多拷贝形式存在的微卫星位点 ,且其中相当一部分以基因家族的形式存在。微卫星DNA家族通常可以在序列分析阶段被识别出来 ,但很多多拷贝位点只有通过一系列后续分析才能被检查出来。这应是鳞翅目昆虫中微卫星位点的优化率相对偏低的主要原因。棉铃虫和松毛虫基因组中三相重复微卫星丰度相对较高 ,从而从某种程度上补偿了这些物种微卫星分离过程中因丰度低、多拷贝位点比例高所带来的困难。棉铃虫微卫星DNA家族侧翼序列中多聚T/A序列的存在表明 ,逆转录转座或逆转录侵染可能是在基因组中形成多拷贝微卫星位点和微卫星DNA家族的重要机制之一

Characteristics of microsatellite DNA in lepidopteran genomes and implications for their isolation

A comparative analysis of microsatellite DNA in lepidopteran insects was carried out, based on our data from microsatellite enriched genomic libraries of lepidopteran insects (the cotton bollworm and the masson pine moth) and a variety of other organisms (the migratory locust, gadoid fishes, fen raft spider and the crested ibis), as well as published data on other lepidopteran insects. Our results suggest that: 1) Both the proportion of the positive clones in genomic libraries and the optimization efficiency of microsatellite loci are much lower in lepidopteran insects than in other organisms (Tables 1, 3);2) A much larger proportion of microsatellite loci bear repetitive flanking region(s) in lepidopteran insects than in other organisms (Table 3) and some are present as multi copy microsatellite DNA families (Fig 1). This means that although the overall abundance of microsatellite loci in lepidopterans is lower, the proportion of multi copy loci is more pronounced. Therefore, the majority of positive clones from genomic libraries are not suitable for use as diagnostic markers in population genetic analysis. This considerably increases the difficulty in microsatellite isolation in lepidopteran insects. 3) There are relatively more trinucleotide microsatellite loci in the cotton bollworm, with the majority of them being a single copy locus (Table 2). This compensates somewhat the difficulty in the isolation of effectively usable microsatellite markers in this species. 4) Null allele appears to be a commonly occurring phenomenon for lepidopteran polymorphic microsatellite loci. It means that there possibly exists an elevated mutation rate in the flanking regions of microsatellite sequences in this group of insects. 5) The existence of poly(T/A) sequences in the repetitive flanking regions of microsatellites (Fig 1) suggests that retrotransposition or retrofection may be involved in the formation of microsatellite DNA families and other multi copy microsatellite loci.