1. Samuel D. Acquah & Arvind Thiagarajan
The effects of molecular noise and size control on variability in the budding yeast cell cycle Di Talia et al., Center for Studies in Physics and Biology Rockefeller University, New York, NY Nature 2009
Presentation
8 December 2011
Samuel D. Acquah & Arvind Thiagarajan

2. Cell Cycle in Yeast

3. 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
Wanted to make a model that accounted for this additional variation among cells with the same size

4. Measurements Yeast transformed with Myo1-GFP fusion
DsRed RFP under control of ACT1 promoter

5. Validation of Size Measurement
DsRed grows exponentially in time and scales proportionally with both ploidy and geometric size estimates

6. 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)

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?

9. Two Stages for G1

10. Validation of Two Stage Model

11. 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