title: Chromosomal duplication is a transient evolutionary solution to stress.
abstract: Aneuploidy, an abnormal number of chromosomes, is a widespread phenomenon found in unicellulars such as yeast, as well as in plants and in mammalians, especially in cancer. Aneuploidy is a genome-scale aberration that imposes a severe burden on the cell, yet under stressful conditions specific aneuploidies confer a selective advantage. This dual nature of aneuploidy raises the question of whether it can serve as a stable and sustainable evolutionary adaptation. To clarify this, we conducted a set of laboratory evolution experiments in yeast and followed the long-term dynamics of aneuploidy under diverse conditions. Here we show that chromosomal duplications are first acquired as a crude solution to stress, yet only as transient solutions that are eliminated and replaced by more efficient solutions obtained at the individual gene level. These transient dynamics of aneuploidy were repeatedly observed in our laboratory evolution experiments; chromosomal duplications gained under stress were eliminated not only when the stress was relieved, but even if it persisted. Furthermore, when stress was applied gradually rather than abruptly, alternative solutions appear to have emerged, but not aneuploidy. Our findings indicate that chromosomal duplication is a first evolutionary line of defense, that retains survivability under strong and abrupt selective pressures, yet it merely serves as a "quick fix," whereas more refined and sustainable solutions take over. Thus, in the perspective of genome evolution trajectory, aneuploidy is a useful yet short-lived intermediate that facilitates further adaptation.
authors.affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Avihu H
authors.initials: AH
authors.lastname: Yona
authors.forename: Yair S
authors.initials: YS
authors.lastname: Manor
authors.forename: Rebecca H
authors.initials: RH
authors.lastname: Herbst
authors.forename: Gal H
authors.initials: GH
authors.lastname: Romano
authors.forename: Amir
authors.initials: A
authors.lastname: Mitchell
authors.forename: Martin
authors.initials: M
authors.lastname: Kupiec
authors.forename: Yitzhak
authors.initials: Y
authors.lastname: Pilpel
authors.forename: Orna
authors.initials: O
authors.lastname: Dahan
mesh_terms: D000782:Aneuploidy; D005075:Biological Evolution; D058674:Chromosome Duplication; D002874:Chromosome Mapping; D002875:Chromosomes / Q000648:ultrastructure*; D004777:Environment; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics; D005800:Genes, Fungal; D006238:Haploidy; D006360:Heat-Shock Proteins / Q000235:genetics; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008957:Models, Genetic; D009369:Neoplasms / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D013696:Temperature
chemical_list: D005656:Fungal Proteins; D006360:Heat-Shock Proteins