Experimental viral evolution at high mutation rate

描述（由申请方提供）：本工作将研究持续高突变率病毒的进化。高突变率的进化预计会通过有害突变的逐步积累来降低种群适应度;高突变率甚至会导致种群灭绝，这一过程被称为致死突变。这一原理是临床上常用诱变药物治疗病毒感染的基础。在这里，病毒（噬菌体）将在体外生长在不同水平的诱变和诱变的进化后果将被研究。在目标1中，将病毒适应度进化与基于估计的有害突变率和病毒生活史参数预测适应度下降量的模型进行比较。将通过以下方式评价模型的稳健性：（i）在预期导致灭绝的高水平和较低水平之间改变突变率，（ii）进化重组和不重组的病毒，以及（iii）研究具有RNA基因组的病毒和具有DNA基因组的其他病毒。一项初步研究已经观察到病毒适应度比预期高得多的进化（由于病毒适应），将特别关注诱变处理期间导致病毒适应的因素。在目的2中，将测定在诱变处理中存活的病毒群体的有益表型（例如，在抑制剂上生长的能力），以解决失败的致命诱变是否可能以适得其反的方式加速进化。在目标3中，在诱变处理后存活的病毒群体和来自这些群体的分离株将在不存在诱变的情况下进化。这里的问题是，诱变处理的突变负荷在处理停止后多久会将适应性抑制到野生型水平以下。总的来说，这些研究应提供一个基础，解释和设计的努力，在体内致死诱变。 公共卫生相关性：一些抗病毒药物会提高病毒的突变率。有人提出，突变率的提高有助于治愈感染（通过“致死突变”消除），但诱变药物往往不成功。这项工作将调查致命诱变的基础，以及突变率的提高是否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.