Ye Chao, Micklem Chris N, Saez Teresa, Das Arijit K, Martins Bruno M C, Locke James C W
Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge CB2 1LR, UK; School of Life Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge CB2 1LR, UK.
Curr Biol. 2024 Dec 16;34(24):5796-5803.e6. doi: 10.1016/j.cub.2024.10.047. Epub 2024 Nov 25.
Cellular processes are dynamic and often oscillatory, requiring precise coordination for optimal cell function. How distinct oscillatory processes can couple within a single cell remains an open question. Here, we use the cyanobacterial circadian clock as a model system to explore the coupling of oscillatory and pulsatile gene circuits. The cyanobacterial circadian clock generates 24-h oscillations in downstream targets to time processes across the day/night cycle. This timing is partly mediated by the clock's modulation of the activity of alternative sigma factors, which direct RNA polymerase to specific promoters. Using single-cell time-lapse microscopy and modeling, we find that the clock modulates the amplitude of expression pulses of the alternative sigma factor RpoD4, which occurs only at cell division. This pulse amplitude modulation (PAM), analogous to AM regulation in radio transmission, allows the clock to robustly generate a 24-h rhythm in rpoD4 expression despite rpoD4's pulsing frequency being non-circadian. By modulating cell division rates, we find that, as predicted by our model, PAM regulation generates the same 24-h period in rpoD4 pulse amplitude over a range of rpoD4 pulse frequencies. Furthermore, we identify a functional significance of rpoD4 expression levels: deletion of rpoD4 results in smaller cell sizes, whereas an increase in rpoD4 expression leads to larger cell sizes in a dose-dependent manner. Thus, our work reveals a link between the cell cycle, clock, and RpoD4 in cyanobacteria and suggests that PAM regulation can be a general mechanism for biological clocks to robustly modulate pulsatile downstream processes.
细胞过程是动态的，且常常是振荡性的，需要精确协调以实现最佳细胞功能。不同的振荡过程如何在单个细胞内耦合仍是一个悬而未决的问题。在这里，我们使用蓝藻生物钟作为模型系统来探索振荡基因回路和脉动基因回路的耦合。蓝藻生物钟在下游靶标中产生24小时振荡，以调节昼夜循环中的各种过程。这种时间调节部分是由生物钟对替代σ因子活性的调节介导的，替代σ因子将RNA聚合酶导向特定的启动子。通过单细胞延时显微镜和建模，我们发现生物钟调节替代σ因子RpoD4表达脉冲的幅度，而RpoD4仅在细胞分裂时出现。这种脉冲幅度调制（PAM）类似于无线电传输中的调幅调节，使得生物钟能够在rpoD4的脉动频率并非昼夜节律的情况下，稳健地产生rpoD4表达的24小时节律。通过调节细胞分裂速率，我们发现，正如我们的模型所预测的，PAM调节在一系列rpoD4脉冲频率范围内，在rpoD4脉冲幅度上产生相同的24小时周期。此外，我们确定了rpoD4表达水平的功能意义：删除rpoD4会导致细胞尺寸变小，而rpoD4表达的增加会以剂量依赖的方式导致细胞尺寸变大。因此，我们的工作揭示了蓝藻中细胞周期、生物钟和RpoD4之间的联系，并表明PAM调节可能是生物钟稳健调节脉动下游过程的一种普遍机制。
