A dual fluorescence protein expression system detects cell cycle dependent protein noise

Area of Science:

• Cellular Biology
• Systems Biology
• Biophysics

Background:

• Phenotypic variation in identical cells arises from stochastic gene expression (noise).
• Noise components (intrinsic and extrinsic) are influenced by inducer concentration and cell cycle phase.
• Understanding noise regulation is crucial for biological processes.

Purpose of the Study:

• To quantify noise component variations across cell cycle phases.
• To investigate the impact of magnesium ions on noise and population homogeneity.
• To compare noise in multi-copy versus single-copy plasmid systems.

Main Methods:

• Utilized a dual-color fluorescence protein reporter system (CFP/YFP) on multi-copy plasmids.
• Induced the lac promoter with Isopropyl β-D-1-thiogalactopyranoside (IPTG).
• Varied Magnesium (Mg²⁺) ion concentrations (2.5 mM and 5 mM) and analyzed cells in different cycle phases.

Main Results:

• A 25% difference in noise was observed between multi-copy and single-copy systems.
• Extrinsic noise was the dominant contributor to total variation, increasing from Lag to Exponential phase and decreasing thereafter.
• 5 mM Mg²⁺ promoted greater population homogeneity than 2.5 mM Mg²⁺.

Conclusions:

• Protein expression noise is tightly regulated by the cell cycle phase and intracellular ionic concentration.
• Extrinsic noise significantly impacts cellular variation during specific growth phases.
• Magnesium ion concentration is a key factor in controlling population homogeneity.