title: Evolutionary adaptation after crippling cell polarization follows reproducible trajectories.
abstract: 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. Initially the bem1∆ lineages rapidly increase in fitness and then slowly reach >90% of the fitness of their BEM1 ancestors at the end of the evolution. 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.
authors.affiliation: FAS Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
authors.forename: Liedewij
authors.initials: L
authors.lastname: Laan
authors.affiliation: FAS Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
authors.forename: John H
authors.initials: JH
authors.lastname: Koschwanez
authors.affiliation: FAS Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Murray
mesh_terms: D000220:Adaptation, Biological; D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency*; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D016681:Genome, Fungal; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D012692:Serial Passage
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004271:DNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; C073129:BEM1 protein, S cerevisiae
keywords: S. cerevisiae; adaptation; cell biology; cell polarity; epistasis; evolutionary biology; experimental evolution; genomics; multi step evolution