Department of Biology, University of York, York YO10 5YW, United Kingdom.
Genome Res. 2010 Aug;20(8):1112-21. doi: 10.1101/gr.100099.109. Epub 2010 Jul 6.
Schistosoma mansoni is a well-adapted blood-dwelling parasitic helminth, persisting for decades in its human host despite being continually exposed to potential immune attack. Here, we describe in detail micro-exon genes (MEG) in S. mansoni, some present in multiple copies, which represent a novel molecular system for creating protein variation through the alternate splicing of short (< or =36 bp) symmetric exons organized in tandem. Analysis of three closely related copies of one MEG family allowed us to trace several evolutionary events and propose a mechanism for micro-exon generation and diversification. Microarray experiments show that the majority of MEGs are up-regulated in life cycle stages associated with establishment in the mammalian host after skin penetration. Sequencing of RT-PCR products allowed the description of several alternate splice forms of micro-exon genes, highlighting the potential use of these transcripts to generate a complex pool of protein variants. We obtained direct evidence for the existence of such pools by proteomic analysis of secretions from migrating schistosomula and mature eggs. Whole-mount in situ hybridization and immunolocalization showed that MEG transcripts and proteins were restricted to glands or epithelia exposed to the external environment. The ability of schistosomes to produce a complex pool of variant proteins aligns them with the other major groups of blood parasites, but using a completely different mechanism. We believe that our data open a new chapter in the study of immune evasion by schistosomes, and their ability to generate variant proteins could represent a significant obstacle to vaccine development.
曼氏血吸虫是一种适应性很强的血液寄生虫，尽管不断受到潜在免疫攻击的威胁，但仍能在其人类宿主中存活数十年。在这里，我们详细描述了曼氏血吸虫的微外显子基因（MEG），其中一些存在于多个拷贝中，这代表了一种通过短（<或=36bp）对称外显子的交替剪接来创建蛋白质变异的新分子系统，这些外显子串联排列。对一个 MEG 家族的三个密切相关的拷贝进行分析，使我们能够追踪到几个进化事件，并提出了一种微外显子产生和多样化的机制。微阵列实验表明，大多数 MEG 在与穿透皮肤后在哺乳动物宿主中建立相关的生命周期阶段中上调。对 RT-PCR 产物的测序允许描述微外显子基因的几种交替剪接形式，突出了这些转录本产生复杂的蛋白质变体池的潜力。通过对迁移的毛蚴和成熟卵的分泌物进行蛋白质组学分析，我们获得了存在这种池的直接证据。整体原位杂交和免疫定位显示，MEG 转录本和蛋白质仅限于暴露于外部环境的腺体或上皮细胞。血吸虫产生复杂的变体蛋白库的能力使它们与其他主要的血液寄生虫群体相匹配，但使用的是完全不同的机制。我们相信，我们的数据为血吸虫免疫逃避的研究开辟了一个新的篇章，它们产生变体蛋白的能力可能是疫苗开发的一个重大障碍。
