Systems biology: On the cell cycle and its switches

Abstract

For the cell-division cycle to progress, hundreds of genes and proteins must be coordinately regulated. Systems-level studies of this cycle show that positive-feedback loops help to keep events in sync.

Figure 1. Cell-cycle synchronizers

a, Skotheim et al. show that positive feedback between Cln1/2-Cdk1 and the transcriptional regulators Whi5 and SBF/MBF is essential for synchronous expression of the G1/S regulon, which is disrupted when positive feedback is brought to a halt in mutant yeast strains that lack the genes CLN1 and CLN2 (cln1Δ cln2Δ). b, Holt and colleagues find that positive feedback between Cdc14 and securin helps to make another step in the cell cycle — separation of sister chromatids at the end of mitosis — happen in unison. In the securin-2A mutant, where this feedback mechanism is lost, sister-chromatid separation does not occur as synchronously.