Scaling of G1 Duration with Population Doubling Time by a Cyclin in Saccharomyces cerevisiae

Abstract

The longer cells stay in particular phases of the cell cycle, the longer it will take these cell populations to increase. However, the above qualitative description has very little predictive value, unless it can be codified mathematically. A quantitative relation that defines the population doubling time (T d) as a function of the time eukaryotic cells spend in specific cell cycle phases would be instrumental for estimating rates of cell proliferation and for evaluating introduced perturbations. Here, we show that in human cells, the length of the G1 phase (T G1) regressed on T d with a slope of 0.75, while in the yeast Saccharomyces cerevisiae, the slope was slightly smaller, at 0.60. On the other hand, cell size was not strongly associated with T d or T G1 in cell cultures that were proliferating at different rates. Furthermore, we show that levels of the yeast G1 cyclin Cln3p were positively associated with rates of cell proliferation over a broad range, at least in part through translational control mediated by a short upstream ORF (uORF) in the CLN3 transcript. Cln3p was also necessary for the proper scaling between T G1 and T d. In contrast, yeast lacking the Whi5p transcriptional repressor maintained the scaling between T G1 and T d. These data reveal fundamental scaling relationships between the duration of eukaryotic cell cycle phases and rates of cell proliferation, point to the necessary role of Cln3p in these relationships in yeast, and provide a mechanistic basis linking Cln3p levels to proliferation rates and the scaling of G1 with doubling time.

Differential scaling between G1 protein production and cell size dynamics promotes commitment to the cell division cycle in budding yeast

“…Moreover, we found a good agreement between Cln3 levels determined via the Cln3-2A-sfGFP fusion in single cells, and recently reported 27 bulk Cln3 measurements across different growth rates (Extended Data Figure 4d). Thus, Cln3-2A-sfGFP expressed from the endogenous CLN3 promoter can be used to determine Cln3 levels in single cells.…”

“…Comparison of single-cell Cln3 measurements with population-based Cln3 data from Blank et al 27 For Extended Data Figure 4d…”

“…Moreover, while the Whi5-dilution model assumes that the increase of cell size during G1 determines the timing of Start, a lack of correlation between the rate of cell proliferation and cell size was recently reported 27 , leaving unclear how the respective model applies across growth conditions.…”

Growth-dependent signals drive an increase in early G1 cyclin concentration to link cell cycle entry with cell growth

“…Previous studies found that levels of Cln3 mRNA and protein are reduced in asynchronous cells growing under poor nutrient conditions (Gallego et al 1997;Parviz and Heideman 1998;Hall et al 1998;Blank et al 2018). However, more recent work discovered that Cln3 is also synthesized in mitosis (Landry et al 2012;Zapata et al 2014).…”

“…Distinguishing models will require a clear understanding of how changing concentrations of Cln3 and Whi5 influence cell cycle entry, and how the concentrations of Cln3 and Whi5 vary during growth and in response to changes in growth rate. However, there are conflicting reports on the behaviors of Cln3 and Whi5 during growth in G1 phase (Tyers et al 1993;Liu et al 2015;Schmoller et al 2015;Zapata et al 2014;Lucena et al 2018;Dorsey et al 2018;Blank et al 2018;Litsios et al 2019;Barber et al 2020). Most previous studies have used quantitative fluorescence microscopy to analyze protein behavior in living cells.…”