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. 2022 Jul 20;11:e76075. doi: 10.7554/eLife.76075

Figure 7. Homeostatic correction of aberrant N/C ratios is explained by a passive nuclear growth model.

(A) Asynchronous WT and pom1Δ whole cells N/C ratio (mean ±STD) in growth medium, from 1 biological replicate. (B) Z-sum projection overlay of the plasma membrane (green) and nuclear membrane (purple) of representative cells at septation (top) and divided (bottom) for WT (left) and pom1Δ (right). White arrow, septum location in the middle of WT cells and decentered for pom1Δ cells leading to asymmetric cell division. Scale bar = 5 µm. (C) N/C ratio over time for selected cells with low (light blue) or high (dark blue) initial N/C ratio. Dashed lines, linear regression for each cohort of cells. (D) Cellular growth rate as a function of a cell’s initial volume. Linear regression is shown in green with a slope γC. (D) N/C ratio change over time as a function of the initial N/C ratio. Experimental data (blue dots), linear fit (blue line), and predicted passive homeostasis N/C ratio behavior (black line) assuming N/C ratio = 7.5% at equilibrium from (A) and cell growth rate γC from (C). See also Figure 7—figure supplement 1. (F) Comparison of cell growth rate γC and the N/C ratio correction rate -γNC. (G–I) Same as D-F but in cells treated with 100 mg/ml CHX to decrease growth rate. (C–I) From two biological replicates.

Figure 7—source data 1. WT and pom1Δ whole cells N/C ratio, cell, and nuclear volumes.
Related to Figure 7A, Figure 7—figure supplement 1.
Figure 7—source data 2. Whole-cell volume, nuclear volume,N/C ratio and cellular growth rate of pom1Δ cells.
Related to Figure 7C–F, Figure 7—figure supplement 1.
Figure 7—source data 3. Whole-cell volume, nuclear volume, N/C ratio and cellular growth rate of pom1Δ cells treated with CHX.
Related to Figure 7G–I.

Figure 7.

Figure 7—figure supplement 1. Quantitation of cellular and nuclear growth in pom1∆ mutant cells.

Figure 7—figure supplement 1.

(A) Wildtype and pom1Δ whole-cell volumes used for Figure 7A. (B) Same as A for nuclear volumes of WT (purple) and pom1Δ (pink) cells. (C) Nuclear and (D) cell volume dynamics for pom1Δ cells. Gray and black lines show tracks corresponding to two selected cells. The gray track represents a cell that divided before the end of the experiment. (E) The standard deviation (STD) of the N/C ratio measured for 91 pom1Δ cells decreases over time. (F) Cellular growth rate γC is independent of the N/C ratio. (G) Nuclear growth rate as a function of the initial N/C ratio over time. Nuclei in cells with high N/C ratio grow slower than nuclei in cells with low N/C ratio. (H) Nuclear growth rate as a function of a cell’s initial volume follows the predicted behavior described in Equation 8. Linear regression is shown in purple. (C–H) n=91 pom1Δ cells.