The effects of molecular noise and size control on variability in the budding yeast cell cycleDi Talia et al., Center for Studies in Physics and BiologyRockefeller University, New York, NYNature 2009 20.309 Presentation 8 December 2011 Samuel D. Acquah & Arvind Thiagarajan
Motivation • Conventional Theory – G1 Length controlled by deterministic cell size requirement • Significant variation in G1 timing among cells of same size invalidates this • New model – both cell size (deterministic) and gene expression (stochastic) control G1 length
Measurements • Yeast transformed with • Myo1-GFP fusion • DsRed RFP under control of ACT1 promoter
Validation of Size Measurement • DsRed grows exponentially in time and scales proportionally with both ploidy and geometric size estimates
Timers v. Sizers • Timer – G1 time independent of size at birth • Mother Cells (slope = -0.1) • Sizer – G1 time exponential in size at birth • Daughter Cells (slope = -0.4, -0.7)
Deviations from Size Control Mechanism • Assume G1 time is sum of size control term, associated noise, and noise not correlated with size • Uncorrelated noise consistently greater than size correlated noise • Is this uncorrelated noise due to gene expression?
Conclusion • G1 duration in budding yeast determined by trafficking and activity of Whi5 • Nuclear Whi5 -> Size Dependent Deterministic Control + Gene Expression Noise • Cytoplasmic Whi5 -> Size Independent Constant Time + Gene Expression Noise