Quantitative characterization of a mitotic cyclin threshold regulating exit from mitosis

Area of Science:

• Cell Biology
• Molecular Biology
• Systems Biology

Background:

• Cyclin abundance is crucial for eukaryotic cell cycle progression.
• Overexpression of mitotic cyclins can induce mitotic arrest.
• Quantitative understanding of cell cycle control near critical thresholds is limited.

Purpose of the Study:

• To quantify the threshold for mitotic block induced by constitutive Clb2 overexpression in budding yeast.
• To investigate the loss of robustness in the cell cycle control system as this threshold is approached.
• To validate a quantitative kinetic model of the budding yeast cell cycle using experimental data.

Main Methods:

• Constitutive overexpression of the mitotic cyclin Clb2 in budding yeast.
• Quantitative analysis of cell cycle behavior and genetic robustness near the mitotic block threshold.
• Utilizing a previously developed quantitative kinetic model of the budding yeast cell cycle to generate predictions.

Main Results:

• The threshold for mitotic block due to Clb2 overexpression was quantified in budding yeast.
• A marked loss of robustness was observed near the threshold, where genetic perturbations became deleterious.
• Model predictions for Clb2 levels and system robustness aligned well with experimental biochemical data.

Conclusions:

• The study provides quantitative insights into cell cycle control and the impact of cyclin levels on genetic robustness.
• The findings validate the predictive power of the quantitative kinetic model for the budding yeast cell cycle.
• Loss of robustness near critical thresholds is a predictable feature of the cell cycle control system.