Spatial relationships within the eukaryotic nucleus are essential for proper nuclear function. In Plasmodium falciparum, the repositioning of chromosomes has been implicated in the regulation of the expression of genes responsible for antigenic variation, and the formation of a single, peri-nuclear nucleolus results in the clustering of rDNA. Nevertheless, the precise spatial relationships between chromosomes remain poorly understood, because, until recently, techniques with sufficient resolution have been lacking. Here we have used chromosome conformation capture and second-generation sequencing to study changes in chromosome folding and spatial positioning that occur during switches in var gene expression. We have generated maps of chromosomal spatial affinities within the P. falciparum nucleus at 25 Kb resolution, revealing a structured nucleolus, an absence of chromosome territories, and confirming previously identified clustering of heterochromatin foci. We show that switches in var gene expression do not appear to involve interaction with a distant enhancer, but do result in local changes at the active locus. These maps reveal the folding properties of malaria chromosomes, validate known physical associations, and characterize the global landscape of spatial interactions. Collectively, our data provide critical information for a better understanding of gene expression regulation and antigenic variation in malaria parasites.

译文

:真核内的空间关系对于适当的核功能至关重要。在恶性疟原虫中,染色体的重新定位与调节负责抗原变异的基因的表达有关,单个核周核仁的形成导致rDNA聚集。尽管如此,染色体之间的精确空间关系仍然知之甚少,因为直到最近,仍缺乏具有足够分辨率的技术。在这里,我们已经使用染色体构象捕获和第二代测序来研究在var基因表达转换期间发生的染色体折叠和空间定位的变化。我们已经以25 Kb的分辨率生成了恶性疟原虫核内染色体空间亲和力的图谱,揭示了结构核仁,染色体区域的缺失,并确认了先前确定的异染色质病灶聚类。我们表明,在var基因表达中的开关似乎并不涉及与远距离增强子的相互作用,但确实会导致活性基因座的局部改变。这些图谱揭示了疟疾染色体的折叠特性,验证了已知的物理关联,并刻画了空间相互作用的全球格局。总体而言,我们的数据为更好地理解疟原虫的基因表达调控和抗原变异提供了关键信息。

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