Drift Barriers to Quality Control When Genes Are Expressed at Different Levels

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Genetics

Background:

• Gene expression is inherently imperfect, occasionally producing toxic products.
• Organisms employ two main strategies to mitigate these errors: global error rate reduction or local tolerance of errors.
• Previous models suggested large populations favor local tolerance, small populations favor global reduction, and intermediate populations exhibit bistability.

Purpose of the Study:

• To investigate how variations in gene expression levels and product vulnerability affect the evolution of error management strategies.
• To re-evaluate the population size-dependent dichotomy of error management solutions.
• To explain observed non-monotonic relationships between population size and transcriptional error rates.

Main Methods:

• Theoretical modeling of selection and genetic drift acting on gene expression error management.
• Analysis of the 'drift barrier' concept, which limits the efficacy of selection against deleterious mutations.
• Incorporation of locus-specific factors like expression level and product sensitivity to errors.

Main Results:

• The strict dichotomy between global and local solutions breaks down.
• A gradual transition in evolved strategies is observed as a function of population size.
• In very small populations, even global error reduction may fail, leading to increased transcriptional error rates.

Conclusions:

• Population size, gene expression levels, and product vulnerability interact to shape the evolution of gene expression error management.
• The findings reconcile theoretical predictions with experimental observations of non-monotonic relationships between population size and transcriptional error rates in various organisms.
• Understanding these evolutionary dynamics is crucial for comprehending cellular robustness and adaptation.