Experimental viral evolution at high mutation rate

描述(申请人提供)：这项工作将调查病毒在持续、高突变率下的进化。高突变率的进化预计会通过有害突变的逐渐积累而降低种群适合度；高突变率甚至可能导致种群灭绝，这一过程被称为致命突变。这一原则是临床上常见的治疗病毒感染的诱变药物的基础。在这里，病毒(噬菌体)将在不同的诱变水平下在体外培养，并将研究这种诱变的进化后果。在目标1中，病毒适应度进化将与基于估计的有害突变率和病毒生活史参数预测适应度衰减量的模型进行比较。该模型的稳健性将通过(I)在预计会导致灭绝的高水平和低水平之间变化，(Ii)在有和没有重组的情况下进化病毒，以及(Iii)研究具有RNA基因组的病毒和其他具有DNA基因组的病毒来评估。一项初步研究已经观察到病毒适应能力的演变比预期的要高得多(由于病毒适应)，并将特别关注在诱变治疗期间促成病毒适应的因素。在目标2中，将对在诱变处理中幸存下来的病毒群体进行有益表型频率的检测(例如，在抑制剂上生长的能力)，以解决致命性突变失败是否会以相反的方式加速进化。在目标3中，在诱变处理中幸存下来的病毒种群和这些种群的分离株将在没有突变的情况下进化。这里的问题是，在停止治疗后，诱变处理产生的突变负荷会在多长时间内将健康水平压低到野生型水平以下。总而言之，这些研究应该为解释和设计体内致命性突变的努力提供基础。 与公共卫生相关：一些抗病毒药物会提高病毒的变异率。有人提出，较高的突变率有助于治愈感染(通过‘致命性突变’而灭绝)，但诱变药物往往不成功。这项工作将调查致命性突变的基础，以及提高的突变率是否反而会导致病毒进化的增强。

DESCRIPTION (provided by applicant): This work will investigate the evolution of viruses subjected to a sustained, high mutation rate. Evolution at a high mutation rate is expected to reduce population fitness by the progressive accumulation of deleterious mutations; high rates can even cause population extinction, a process known as lethal mutagenesis. This principle underlies the common use of mutagenic, drugs to treat viral infections clinically. Here, viruses (bacteriophages) will be grown in vitro at different levels of mutagenesis and the evolutionary consequences of that mutagenesis will be studied. In Aim 1, viral fitness evolution will be compared with a model predicting the amount of fitness decline based on the estimated deleterious mutation rate and viral life history parameters. Robustness of the model will be evaluated by (i) varying the mutation rate between high levels expected to cause extinction and lower levels, (ii) evolving viruses with and without recombination, and (iii) studying viruses with RNA genomes and others with DNA genomes. A preliminary study already observed the evolution of much higher viral fitness than predicted (due to viral adaptation), and special attention will be given to the factors contributing to viral adaptation during mutagenic treatment. In Aim 2, populations of viruses surviving mutagenic treatment will be assayed for elevated frequencies of beneficial phenotypes (e.g., ability to grow on inhibitors), to address whether failed lethal mutagenesis might accelerate evolution in counter-productive ways. In Aim 3, viral populations that survived mutagenic treatment and isolates from those populations will be evolved in the absence of mutagenesis. The question here is how long the mutational load from mutagenic treatment will depress fitness below wild-type levels after treatment is stopped. Collectively, these studies should provide a foundation for interpreting and designing efforts at lethal mutagenesis in vivo. PUBLIC HEALTH RELEVANCE: Some antiviral drugs elevate the mutation rate of the virus. It has been proposed that the elevated mutation rate contributes to curing the infection (extinction through 'lethal mutagenesis'), but the mutagenic drugs are often not successful. The work here will investigate the foundations of lethal mutagenesis and whether the elevated mutation rate might instead lead to enhanced viral evolution.