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 genomescale
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. Herewe showthat 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.
Ourfindings indicate that chromosomalduplicationis afirst
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.
Aneuploidy, an abnormal number of chromosomes, is a widespreadphenomenon found in unicellulars such as yeast, as well as in plantsand in mammalians, especially in cancer. Aneuploidy is a genomescaleaberration that imposes a severe burden on the cell, yet understressful conditions specific aneuploidies confer a selective advantage.This dual nature of aneuploidy raises the question of whetherit can serve as a stable and sustainable evolutionary adaptation. Toclarify this, we conducted a set of laboratory evolution experimentsin yeast and followed the long-term dynamics of aneuploidy underdiverse conditions. Herewe showthat chromosomal duplications arefirst acquired as a crude solution to stress, yet only as transient solutionsthat are eliminated and replaced by more efficient solutionsobtained at the individual gene level. These transient dynamics ofaneuploidy were repeatedly observed in our laboratory evolutionexperiments; chromosomal duplications gained under stress wereeliminated not only when the stress was relieved, but even if it persisted.Furthermore, when stress was applied gradually rather thanabruptly, alternative solutions appear to have emerged, but not aneuploidy.Ourfindings indicate that chromosomalduplicationis afirstevolutionary line of defense, that retains survivability under strongand abrupt selective pressures, yet it merely serves as a “quick fix,”whereas more refined and sustainable solutions take over. Thus, inthe perspective of genome evolution trajectory, aneuploidy is a usefulyet short-lived intermediate that facilitates further adaptation.
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