A simple molecular mechanism explains multiple patterns of cell-size regulation

Area of Science:

• Cell Biology
• Biophysics
• Systems Biology

Background:

• Cells maintain stable size trajectories during the cell cycle using diverse strategies.
• Observed microbial cell size control ranges from pure sizer to pure adder mechanisms.
• The biological basis for this spectrum of behaviors remains largely unexplained.

Purpose of the Study:

• To analyze a molecular mechanism explaining the spectrum of cell size control behaviors.
• To investigate how protein dynamics give rise to interpolating adder-sizer strategies.
• To reconcile adder and critical size behaviors within a unified biophysical framework.

Main Methods:

• Analysis of a molecular size-control mechanism using experimental data from Saccharomyces cerevisiae.
• Modeling cell size control based on the accumulation of an activator protein that titrates an inhibitor.
• Investigating the model's behavior across different initial cell sizes.

Main Results:

• A single molecular mechanism can generate behaviors interpolating between adder and sizer strategies.
• The model exhibits a sizer regime for small initial cell sizes.
• For larger initial cell sizes, the model demonstrates an imperfect adder regime, aligning with experimental findings.

Conclusions:

• Adder and sizer behaviors may represent different dynamical regimes of a single biophysical mechanism.
• Cell size control is effectively explained by the interplay of protein accumulation and titration.
• This unified model provides a fundamental insight into cell cycle regulation and size homeostasis.