Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
Proc Natl Acad Sci U S A. 2010 Jul 27;107(30):13550-5. doi: 10.1073/pnas.1001107107. Epub 2010 Jul 9.
A key circuit in the response of cells to damage is the p53-mdm2 feedback loop. This circuit shows sustained, noisy oscillations in individual human cells following DNA breaks. Here, we apply an engineering approach known as systems identification to quantify the in vivo interactions in the circuit on the basis of accurate measurements of its power spectrum. We obtained oscillation time courses of p53 and Mdm2 protein levels from several hundred cells and analyzed their Fourier spectra. We find characteristic spectra with distinct low-frequency components that are well-described by a third-order linear model with white noise. The model identifies the sign and strength of the known interactions, including a negative feedback loop between p53 and its upstream regulator. It also implies that noise can trigger and maintain the oscillations. The model also captures the power spectra of p53 dynamics without DNA damage. Parameters such as noise amplitudes and protein lifetimes are estimated. This approach employs natural biological noise as a diagnostic that stimulates the system at many frequencies at once. It seems to be a useful way to find the in vivo design of circuits and may be applied to other systems by monitoring their power spectrum in individual cells.
细胞对损伤反应的一个关键回路是 p53-mdm2 反馈回路。在 DNA 断裂后，单个人类细胞中的这个回路会表现出持续的、嘈杂的震荡。在这里，我们应用一种称为系统识别的工程方法，根据其功率谱的精确测量来量化回路中的体内相互作用。我们从数百个细胞中获得了 p53 和 Mdm2 蛋白水平的震荡时间过程，并分析了它们的傅立叶频谱。我们发现了具有独特低频分量的特征谱，这些谱可以很好地用具有白噪声的三阶线性模型来描述。该模型确定了已知相互作用的符号和强度，包括 p53 与其上游调节剂之间的负反馈回路。它还表明，噪声可以触发和维持震荡。该模型还可以捕捉没有 DNA 损伤时的 p53 动力学的功率谱。估计了噪声幅度和蛋白质寿命等参数。这种方法利用自然生物噪声作为诊断工具，同时以多种频率刺激系统。通过在单个细胞中监测其功率谱，似乎是找到回路体内设计的一种有用方法，并可应用于其他系统。
