Many biological systems can switch between two distinct states. Once switched, the system remains stable for a period of time and may switch back to its original state. A gene network with bistability is usually required for the switching and stochastic effect in the gene expression may induce such switching. A typical bistable system allows one-directional switching, in which the switch from the low state to the high state or from the high state to the low state occurs under different conditions. It is usually difficult to enable bi-directional switching such that the two switches can occur under the same condition. Here, we present a model consisting of standard positive feedback loops and an extra negative feedback loop with a time delay to study its capability to produce bi-directional switching induced by noise. We find that the time delay in the negative feedback is critical for robust bi-directional switching and the length of delay affects its switching frequency.

中文翻译：

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噪声引起的双向切换的延迟模型

许多生物系统可以在两种不同的状态之间切换。一旦切换，系统会在一段时间内保持稳定，并可能切换回原始状态。转换通常需要具有双稳定性的基因网络，基因表达中的随机效应可能会诱导这种转换。典型的双稳态系统允许单向切换，其中从低态到高态或从高态到低态的切换发生在不同的条件下。通常很难启用双向切换，使得两个切换可以在相同条件下发生。在这里，我们提出了一个由标准正反馈回路和具有时间延迟的额外负反馈回路组成的模型，以研究其产生由噪声引起的双向切换的能力。