Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK; Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK.
Université Côte d'Azur, INSERM, CNRS, IRCAN, 06107 Nice, France.
Cell Rep. 2017 Oct 17;21(3):732-744. doi: 10.1016/j.celrep.2017.09.046.
The joint contribution of pre-existing and de novo genetic variation to clonal adaptation is poorly understood but essential to designing successful antimicrobial or cancer therapies. To address this, we evolve genetically diverse populations of budding yeast, S. cerevisiae, consisting of diploid cells with unique haplotype combinations. We study the asexual evolution of these populations under selective inhibition with chemotherapeutic drugs by time-resolved whole-genome sequencing and phenotyping. All populations undergo clonal expansions driven by de novo mutations but remain genetically and phenotypically diverse. The clones exhibit widespread genomic instability, rendering recessive de novo mutations homozygous and refining pre-existing variation. Finally, we decompose the fitness contributions of pre-existing and de novo mutations by creating a large recombinant library of adaptive mutations in an ensemble of genetic backgrounds. Both pre-existing and de novo mutations substantially contribute to fitness, and the relative fitness of pre-existing variants sets a selective threshold for new adaptive mutations.
遗传变异对无性系适应的共同贡献尚未得到充分理解，但对于设计成功的抗菌或癌症治疗方法至关重要。为了解决这个问题，我们进化了遗传上多样化的出芽酵母 S. cerevisiae 种群，这些种群由具有独特单倍型组合的二倍体细胞组成。我们通过时间分辨的全基因组测序和表型分析，研究了这些种群在化疗药物选择性抑制下的无性系进化。所有种群都经历了由新生突变驱动的无性系扩张，但仍然具有遗传和表型多样性。克隆表现出广泛的基因组不稳定性，使隐性新生突变纯合，并改善了预先存在的变异。最后，我们通过在一组遗传背景中创建适应性突变的大型重组文库，分解预先存在和新生突变的适应性贡献。预先存在和新生突变都对适应性有很大贡献，预先存在变体的相对适应性为新的适应性突变设定了选择阈值。
