Bimodal gene expression in noncooperative regulatory systems

Area of Science:

• Systems Biology
• Molecular Biology
• Theoretical Biology

Background:

• Bimodal gene expression enhances cellular survival in changing environments.
• Previously, bimodality was linked to transcription factor cooperativity or feedback loops.
• The possibility of noncooperative binding causing bimodality in open-loop systems was unclear.

Purpose of the Study:

• To investigate if noncooperative transcription factor binding can lead to gene expression bimodality in an open-loop system.
• To develop a theoretical model for understanding gene expression dynamics.
• To provide a predictive tool for experimental design.

Main Methods:

• Developed a theoretical model of a two-step gene expression cascade.
• Analyzed a deterministically monostable system with nonlinear gene regulation.
• Introduced a geometric construction to predict the onset of bimodality.

Main Results:

• Demonstrated that a unimodal transcription factor distribution can yield a bimodal steady-state output without cooperative binding.
• Showed that gene expression can switch between unimodal and bimodal states by varying inducer/corepressor concentrations.
• The geometric construction accurately predicts bimodality based on gene bursting and dose-response parameters.

Conclusions:

• Noncooperative transcription factor binding in open-loop systems can generate gene expression bimodality.
• The geometric construction offers a valuable tool for interpreting experimental results and designing new studies.
• Findings contribute to understanding cellular survival strategies in fluctuating environments.