The ATR kinase of Trypanosoma brucei links DNA damage signalling during antigenic variation with regulation of RNA Polymerase I transcribed surface antigens. RNAseq in an inducible ATR kinase knockdown in T. brucei

Trypanosoma brucei evades mammalian immunity by using recombination to switch its surface expressed Variant Surface Glycoprotein (VSG), whilst ensuring only one of many subtelomeric multigene VSG expression sites are transcribed at a time. DNA repair activities have been implicated only in catalysis of VSG switching by recombination, not transcriptional control. How VSG switching is signalled to guide the appropriate reaction, or to integrate switching into parasite growth, is unknown. Here we show that loss of ATR, a DNA damage signalling protein kinase, is lethal, causing nuclear genome instability and increased VSG switching through VSG-localised damage. Furthermore, ATR loss leads to increased transcription of silent VSG expression sites and expression of mixed VSGs on the cell surface, effects that are associated with altered localisation of RNA Polymerase I and VEX1. This work therefore reveals that ATR acts in antigenic variation both through DNA damage signalling and surface antigen expression control.

布氏锥虫（Trypanosoma brucei）通过重组机制切换其表面表达的变异表面糖蛋白（Variant Surface Glycoprotein，VSG），同时确保众多亚端粒多拷贝VSG表达位点中仅有一个可被同时转录。既往研究仅将DNA修复活性与重组介导的VSG切换催化过程相关联，并未涉及转录调控环节。目前，学界尚未明确VSG切换如何被信号传导以引导恰当的反应，或是将切换过程整合到寄生虫的生长周期中。
本研究证实，作为DNA损伤信号激酶的ATR缺失会引发致命表型，导致细胞核基因组不稳定，并通过VSG区域的DNA损伤增加VSG切换频率。此外，ATR缺失会使沉默的VSG表达位点转录水平上调，且细胞表面会同时表达多种VSG亚型，这些效应与RNA聚合酶I及VEX1的定位异常相关。综上，本研究揭示了ATR可通过DNA损伤信号传导与表面抗原表达调控两种途径参与抗原变异过程。