Few crucial links assure checkpoint efficiency in the yeast cell-cycle network.
BACKGROUND
The ability of cells to complete mitosis with high fidelity relies on elaborate checkpoint mechanisms. We study S- and M-phase checkpoint responses in silico in the budding yeast with a stochastic dynamical model for the cell-cycle. We aim to provide an unbiased functional classification of network interactions that reflect the contribution of each link to checkpoint efficiency in the presence of cellular fluctuations.


RESULTS
We developed an algorithm BNetDyn to compute stochastic dynamical trajectories for an input gene network and its structural perturbations. User specified output measures like the mutual information between trigger and output nodes are then evaluated on the stationary state of the Markov process. Systematic perturbations of the yeast cell-cycle model by Li et al. classify each link according to its effect on checkpoint efficiencies and stabilities of the main cell-cycle phases. This points to the crosstalk in the cascades downstream of the SBF/MBF transcription activator complexes as determinant for checkpoint optimality; a finding that consistently reflects recent experiments. Finally our stochastic analysis emphasizes how dynamical stability in the yeast cell-cycle network crucially relies on backward inhibitory circuits next to forward induction.


BACKGROUND
C++ source code and network models can be downloaded at http://www.vital-it.ch/Software/
Stoll
Gautier
G
Swiss Institute of Experimental Cancer Research, ISREC, NCCR Molecular Oncology CH-1066 Epalinges, Switzerland.
Rougemont
Jacques
J
Naef
Félix
F
D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D003198:Computer Simulation; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D018816:Genes, cdc / Q000502:physiology*; D008954:Models, Biological; D015233:Models, Statistical; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013269:Stochastic Processes
D018797:Cell Cycle Proteins; D029701:Saccharomyces cerevisiae Proteins