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How selection affects phenotypic fluctuation.

Ito Y, Toyota H, Kaneko K, Yomo T - Mol. Syst. Biol. (2009)

Bottom Line: However, as fluctuation can increase phenotypic diversity, similar to mutation, it may contribute to the survival of individuals even under a single selective environment.To discuss whether the fluctuation increases over the course of evolution, cycles of mutation and selection for higher GFP fluorescence were carried out in Escherichia coli.In addition to the average phenotypic change by genetic mutation, the observed increase in phenotypic fluctuation acts as an evolutionary strategy to produce an extreme phenotype under severe selective environments.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan.

ABSTRACT
The large degree of phenotypic fluctuation among isogenic cells highlighted by recent studies on stochastic gene expression confers fitness on some individuals through a 'bet-hedging' strategy, when faced with different selective environments. Under a single selective environment, the fluctuation may be suppressed through evolution, as it prevents maintenance of individuals around the fittest state and/or function. However, as fluctuation can increase phenotypic diversity, similar to mutation, it may contribute to the survival of individuals even under a single selective environment. To discuss whether the fluctuation increases over the course of evolution, cycles of mutation and selection for higher GFP fluorescence were carried out in Escherichia coli. Mutant genotypes possessing broad GFP fluorescence distributions with low average values emerged under strong selection pressure. These 'broad mutants' appeared independently on the phylogenetic tree and increased fluctuations in GFP fluorescence were attributable to the variance in mRNA abundance. In addition to the average phenotypic change by genetic mutation, the observed increase in phenotypic fluctuation acts as an evolutionary strategy to produce an extreme phenotype under severe selective environments.

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Related in: MedlinePlus

Phenotypic distributions of broad and narrow mutants. (A–C) Histograms of log(fluorescence intensity (FI)/forward scattering (FS)) measured by FCM for each of the population of HLG10-6 (A), examples of broad mutants HLG2nd-5 (B) and narrow mutants HLG2nd-2 (C). The histograms (A–C) show the results of the re-cloning experiments. The peak position of HLG10-6 is indicated with the vertical line as a reference. (D) Peak value versus full-width at half-maximum. These values were obtained from the histogram of log(FI/FS) for each clone represented in Figure 1C. Colours and symbols are as in Figure 1C. Broad mutants are encircled by a red broken line.
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f2: Phenotypic distributions of broad and narrow mutants. (A–C) Histograms of log(fluorescence intensity (FI)/forward scattering (FS)) measured by FCM for each of the population of HLG10-6 (A), examples of broad mutants HLG2nd-5 (B) and narrow mutants HLG2nd-2 (C). The histograms (A–C) show the results of the re-cloning experiments. The peak position of HLG10-6 is indicated with the vertical line as a reference. (D) Peak value versus full-width at half-maximum. These values were obtained from the histogram of log(FI/FS) for each clone represented in Figure 1C. Colours and symbols are as in Figure 1C. Broad mutants are encircled by a red broken line.

Mentions: Figure 1B and C show an outline of the evolutionary process used in this study. The selection threshold value, defined as log(FI/FS) at 99.8 percentile among the cells in a population, increased during the evolutionary experiment. Twelve clones were picked at random from the last selection cycle of each generation. The cell distribution of FI/FS was measured (Figure 2 and Supplementary Figure S1) and the RP gene for each clone was sequenced (Supplementary Figure S2). The selection threshold values for these randomly picked clones also increased with the generations (Figure 1B). Sequence analysis of these clones revealed a phylogenetic tree with diverged branches. These observations indicated that the evolutionary experiment succeeded in increasing the selection threshold value as designed but retained some diversity in the evolved population.


How selection affects phenotypic fluctuation.

Ito Y, Toyota H, Kaneko K, Yomo T - Mol. Syst. Biol. (2009)

Phenotypic distributions of broad and narrow mutants. (A–C) Histograms of log(fluorescence intensity (FI)/forward scattering (FS)) measured by FCM for each of the population of HLG10-6 (A), examples of broad mutants HLG2nd-5 (B) and narrow mutants HLG2nd-2 (C). The histograms (A–C) show the results of the re-cloning experiments. The peak position of HLG10-6 is indicated with the vertical line as a reference. (D) Peak value versus full-width at half-maximum. These values were obtained from the histogram of log(FI/FS) for each clone represented in Figure 1C. Colours and symbols are as in Figure 1C. Broad mutants are encircled by a red broken line.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2683726&req=5

f2: Phenotypic distributions of broad and narrow mutants. (A–C) Histograms of log(fluorescence intensity (FI)/forward scattering (FS)) measured by FCM for each of the population of HLG10-6 (A), examples of broad mutants HLG2nd-5 (B) and narrow mutants HLG2nd-2 (C). The histograms (A–C) show the results of the re-cloning experiments. The peak position of HLG10-6 is indicated with the vertical line as a reference. (D) Peak value versus full-width at half-maximum. These values were obtained from the histogram of log(FI/FS) for each clone represented in Figure 1C. Colours and symbols are as in Figure 1C. Broad mutants are encircled by a red broken line.
Mentions: Figure 1B and C show an outline of the evolutionary process used in this study. The selection threshold value, defined as log(FI/FS) at 99.8 percentile among the cells in a population, increased during the evolutionary experiment. Twelve clones were picked at random from the last selection cycle of each generation. The cell distribution of FI/FS was measured (Figure 2 and Supplementary Figure S1) and the RP gene for each clone was sequenced (Supplementary Figure S2). The selection threshold values for these randomly picked clones also increased with the generations (Figure 1B). Sequence analysis of these clones revealed a phylogenetic tree with diverged branches. These observations indicated that the evolutionary experiment succeeded in increasing the selection threshold value as designed but retained some diversity in the evolved population.

Bottom Line: However, as fluctuation can increase phenotypic diversity, similar to mutation, it may contribute to the survival of individuals even under a single selective environment.To discuss whether the fluctuation increases over the course of evolution, cycles of mutation and selection for higher GFP fluorescence were carried out in Escherichia coli.In addition to the average phenotypic change by genetic mutation, the observed increase in phenotypic fluctuation acts as an evolutionary strategy to produce an extreme phenotype under severe selective environments.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan.

ABSTRACT
The large degree of phenotypic fluctuation among isogenic cells highlighted by recent studies on stochastic gene expression confers fitness on some individuals through a 'bet-hedging' strategy, when faced with different selective environments. Under a single selective environment, the fluctuation may be suppressed through evolution, as it prevents maintenance of individuals around the fittest state and/or function. However, as fluctuation can increase phenotypic diversity, similar to mutation, it may contribute to the survival of individuals even under a single selective environment. To discuss whether the fluctuation increases over the course of evolution, cycles of mutation and selection for higher GFP fluorescence were carried out in Escherichia coli. Mutant genotypes possessing broad GFP fluorescence distributions with low average values emerged under strong selection pressure. These 'broad mutants' appeared independently on the phylogenetic tree and increased fluctuations in GFP fluorescence were attributable to the variance in mRNA abundance. In addition to the average phenotypic change by genetic mutation, the observed increase in phenotypic fluctuation acts as an evolutionary strategy to produce an extreme phenotype under severe selective environments.

Show MeSH
Related in: MedlinePlus