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Updated: Aug 7, 2026
Two- and Three-Dimensional Live Cell Imaging of DNA Damage Response Proteins
Published on: September 28, 2012
Elucidating the digital control mechanism for DNA damage repair with the p53-Mdm2 system: single cell data analysis
1University of Delaware, Department of Chemical Engineering, Newark, DE 19716, USA. ogunnaike@che.udel.edu
Abstract:
Recent experimental evidence about DNA damage response using the p53-Mdm2 system has raised some fundamental questions about the control mechanism employed. In response to DNA damage, an ensemble of cells shows a damped oscillation in p53 expression whose amplitude increases with increased DNA damage--consistent with 'analogue' control. Recent experimental results, however, show that the single cell response is a series of discrete pulses in p53; and with increase in DNA damage, neither the height nor the duration of the pulses change, but the mean number of pulses increase--consistent with 'digital' control. Here we present a system engineering model that uses published data to elucidate this mechanism and resolve the dilemma of how digital behaviour at the single cell level can manifest as analogue ensemble behaviour. First, we develop a dynamic model of the p53-Mdm2 system that produces non-oscillatory responses to a stress signal. Second, we develop a probability model of the distribution of pulses in a cell population, and combine the two with the simplest digital control algorithm to show how oscillatory responses whose amplitudes grow with DNA damage can arise from single cell behaviour in which each single pulse response is independent of the extent of DNA damage. A stochastic simulation of the hypothesized control mechanism reproduces experimental observations remarkably well.
Insights
The p53-Mdm2 system exhibits digital control at the single-cell level, with DNA damage increasing pulse frequency, not pulse amplitude. This digital behavior explains the observed analogue-like oscillations in cell populations.
Area of Science:
- Molecular Biology
- Systems Biology
- Cellular Dynamics
Background:
- The DNA damage response (DDR) involves the p53-Mdm2 system, crucial for cell cycle regulation and apoptosis.
- Previous studies suggested analogue control of p53 expression, showing damped oscillations with amplitude proportional to DNA damage.
- Recent single-cell experiments revealed discrete p53 pulses, with DNA damage increasing pulse number, not amplitude or duration, suggesting digital control.
Purpose of the Study:
- To develop a systems engineering model that reconciles single-cell digital control with population-level analogue behavior in the p53-Mdm2 system.
- To elucidate the mechanism by which digital single-cell responses can lead to analogue ensemble behavior in response to DNA damage.
Main Methods:
- Development of a dynamic model for the p53-Mdm2 system, simulating non-oscillatory responses to stress signals.
- Construction of a probability model to describe pulse distribution within a cell population.
- Integration of dynamic and probability models with a digital control algorithm, validated by stochastic simulations.
Main Results:
- The model demonstrates how digital control at the single-cell level (independent pulse characteristics) can generate analogue-like ensemble oscillations.
- Simulated oscillatory responses showed amplitudes that increase with simulated DNA damage, mirroring experimental observations.
- Stochastic simulations accurately reproduced the experimental findings of p53 pulse dynamics in response to varying DNA damage levels.
Conclusions:
- The study resolves the apparent paradox between single-cell digital and population-level analogue responses in the p53-Mdm2 DNA damage pathway.
- A simple digital control mechanism, where DNA damage increases pulse frequency, effectively explains the observed dose-dependent analogue behavior in cell populations.
- The findings highlight the importance of systems engineering approaches in understanding complex biological regulatory networks.
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