摘要： SSR检测新方法介绍
         新技术方法的产生发展从来都是来势汹汹、锐不可当的，SSR的检测亦是如此！自从生命科学迈入到ATCG时代以来，传统的仅仅靠“跑电泳，比大小”的定性分析，已经越来越无法满足科研工作者对“准确、高效、定量”的要求了。二代高通量测序技术的发展，让这一目标成为现实，天昊生物创新技术—SSRseq，把SSR的“序列信息”及“比例信息”一网打尽！下面就跟随小编看看SSR检测的“前世今生”。
 
什么是SSR？
        SSR (Simple Sequence Repeats，简单序列重复)，或称STR（Short Tandem Repeat，短片段串联重复）或者Microsatellites（微卫星），广泛的存在于真核生物基因组中。大多数SSRs是非编码序列，可以影响基因表达、剪接、蛋白序列及基因组结构等（1-5）。SSR长度突变频率在每一世代每个位点大概是10-7到10-3之间（6），这远远高于单个碱基10-9左右的突变频率（7-8），从而在基因组中产生了更具多样性的SSRs。尽管SSR序列自身具有高度的变异性，但是它侧翼区域的序列却在物种内具有很高保守性，有时这种保守型甚至在物种间存在（9-12）。SSR相较与其他遗传变异具有几方面特点，包括共显性、高度可重复性和DNA检测需要量少等（13-16）。更重要的是，这种SSR序列的多样性和它侧翼序列保守性的结合，使它成为一种理想的遗传分子标记。的确，SSRs已经在包括DNA指纹图谱分析、基因作图、亲缘关系鉴定、分子辅助育种、遗传多样性分析、种子纯度及品系鉴定中发挥着重要的作用（16-20）。
 
SSR多样性的产生原因及传统检测的不足
        SSR多样性产生的最主要原因是在SSR复制过程中DNA聚合酶固有的“滑移”现象（Slippage）造成的(21-27)，这种滑移现象同样可以发生在体外，导致错误的SSR等位基因并增加了SSR准确分型的难度。而且，基于琼脂糖凝胶电泳、聚丙烯酰胺凝胶电泳、毛细管电泳这些目前常用的SSR检测方法，普遍存在着分辨率不高、不够准确、效率及通量不高等问题。例如，目前在冬菇、黄麻和木豆中进行的DNA指纹图谱分析仅仅用到25、28和48个SSR位点（28-30）。这些有限的SSRs不足以构建高质量SSR指纹图谱用于区分亲缘性高物种间的关系。全基因组重测序虽然一次可以检测大量SSR位点（25, 31-32），但是SSR序列仅仅占整个基因组的很小部分，例如人类基因组中的SSR只占3%左右（33），因此全基因组重测序会获得很多我们关心的SSR以外的冗余序列，这就稀释了所测有用数据的比例，使得SSR位点的测序深度很难超过10-100X（25），这样在合理的测序价格内，利用全基因组重测序的方法就难以得到准确性高的SSR分型。另外，用全基因组重测序进行SSR分型还会导致某些SSR位点的扩增偏好性以及SSR重复序列较高难度的数据分析等问题（34-36）。
 
       天昊生物自主研发的基于二代测序技术的SSR分型新方法--SSRseq，这种方法几乎克服了现存所有检测方法的不足，尤其适合对多SSR位点、超高深度的分型，准确度高，并且分辨率达到单碱基的水平。因此适合所有二倍体动植物及真核微生物的SSR位点分型。另外，我们还成功对六倍体植物—油茶进行了SSR分型。对于多倍体物种来说，我们的SSRseq可以提供不同等位基因的比例数据，从而提高了多倍体物种遗传多样性分析的准确度，获得更加清晰的遗传结构图。
 
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部分内容来源：doi: 10.1093/nar/gkx093
 
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