Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3220, USA.
Proc Natl Acad Sci U S A. 2012 Mar 6;109(10):3874-8. doi: 10.1073/pnas.1116360109. Epub 2012 Feb 21.
Organismal fitness depends on the ability of gene networks to function robustly in the face of environmental and genetic perturbations. Understanding the mechanisms of this stability is one of the key aims of modern systems biology. Dissecting the basis of robustness to mutation has proven a particular challenge, with most experimental models relying on artificial DNA sequence variants engineered in the laboratory. In this work, we hypothesized that negative regulatory feedback could stabilize gene expression against the disruptions that arise from natural genetic variation. We screened yeast transcription factors for feedback and used the results to establish ROX1 (Repressor of hypOXia) as a model system for the study of feedback in circuit behaviors and its impact across genetically heterogeneous populations. Mutagenesis experiments revealed the mechanism of Rox1 as a direct transcriptional repressor at its own gene, enabling a regulatory program of rapid induction during environmental change that reached a plateau of moderate steady-state expression. Additionally, in a given environmental condition, Rox1 levels varied widely across genetically distinct strains; the ROX1 feedback loop regulated this variation, in that the range of expression levels across genetic backgrounds showed greater spread in ROX1 feedback mutants than among strains with the ROX1 feedback loop intact. Our findings indicate that the ROX1 feedback circuit is tuned to respond to perturbations arising from natural genetic variation in addition to its role in induction behavior. We suggest that regulatory feedback may be an important element of the network architectures that confer mutational robustness across biology.
生物体的适应性取决于基因网络在面对环境和遗传干扰时能够稳健运作的能力。理解这种稳定性的机制是现代系统生物学的主要目标之一。解析对突变的稳健性的基础被证明是一个特别的挑战，大多数实验模型都依赖于在实验室中设计的人工 DNA 序列变体。在这项工作中，我们假设负反馈调节可以稳定基因表达，防止由自然遗传变异引起的干扰。我们筛选了酵母转录因子的反馈机制，并利用这些结果建立了 ROX1（Hypoxia Repressor）作为研究电路行为中的反馈及其在遗传异质群体中的影响的模型系统。诱变实验揭示了 Rox1 的机制是其自身基因的直接转录抑制剂，使其在环境变化时能够迅速诱导表达，并达到适度的稳定表达水平。此外，在给定的环境条件下，不同遗传背景的菌株之间 Rox1 的水平差异很大；ROX1 反馈回路调节了这种变化，即在遗传背景下的表达水平范围在 ROX1 反馈突变体中比在 ROX1 反馈回路完整的菌株中更为广泛。我们的研究结果表明，ROX1 反馈回路不仅在诱导行为中起作用，还能适应自然遗传变异所产生的干扰。我们认为，调节反馈可能是赋予生物学中突变稳健性的网络架构的重要组成部分。
