Sequences from Evolutionary adaptation after crippling cell polarization follows reproducible trajectories (Liedewij Laan, John H Koschwanez, and Andrew W Murray, eLife, 2015 Oct 1)

Cells are organized by functional modules, which typically contain components whose removal severely compromises the module's function. Despite their importance, these components are not absolutely conserved between parts of the tree of life, suggesting that cells can evolve to perform the same biological functions with different proteins. We evolved Saccharomyces cerevisiae for 1000 generations without the important polarity gene BEM1. At the end of the evolution the bem1? lineages rapidly increase in fitness and then slowly reach >90% of the fitness of their BEM1 ancestors. Sequencing their genomes and monitoring polarization reveals a common evolutionary trajectory, with a fixed sequence of adaptive mutations, each improving cell polarization by inactivating proteins. Our results show that organisms can be evolutionarily robust to physiologically destructive perturbations and suggest that recovery by gene inactivation can lead to rapid divergence in the parts list for cell biologically important functions.

细胞以功能模块（functional module）为基本单位进行组织，此类模块通常包含若干组分，移除这些组分将严重削弱模块的功能。尽管这些组分至关重要，但它们在生命之树的不同演化分支间并非绝对保守，这表明细胞可通过演化，借助不同的蛋白质完成相同的生物学功能。我们针对酿酒酵母（Saccharomyces cerevisiae）开展了1000代的演化实验，使其关键极性基因BEM1缺失。演化实验结束后，bem1缺陷谱系的适应度快速提升，随后缓慢达到其BEM1野生型祖先适应度的90%以上。对其基因组进行测序并监测细胞极性过程后发现，所有谱系均遵循一套共同的演化轨迹：存在一套固定的适应性突变序列，每一轮突变均通过灭活蛋白质来增强细胞极性。我们的研究结果表明，生物体对于生理破坏性扰动具有演化鲁棒性；同时也提示，通过基因失活实现的功能恢复，可导致细胞重要生物学功能的组分清单快速发生分化。