Cells sense and respond to signals in their local environment by activating signaling cascades that lead to phenotypic changes. Differences in these signals can be discriminated at the population level; however, single cells have been thought to be limited in their capacity to distinguish ligand doses due to signaling noise. We describe here the rational development of a genetically encoded FoxO1 sensor, which serves as a down-stream readout of insulin growth factor-phosphatidylinositol 3-kinase IGF-PI3K-AKT signaling pathway activity. With this reporter, we tracked individual cell responses to multiple IGF-I doses, pathway inhibitors, and repeated treatments. We observed that individual cells can discriminate multiple IGF-I doses, and these responses are sustained over time, are reproducible at the single-cell level, and display cell-to-cell heterogeneity. These studies imply that cell-to-cell variation in signaling responses is biologically meaningful and support the endeavor to elucidate mechanisms of cell signaling at the level of the individual cell.

细胞通过激活导致表型改变的信号级联反应来感知并响应其局部环境中的信号。这些信号的差异可以在人群水平上加以区分。然而，由于信号噪声，已经认为单细胞区分配体剂量的能力受到限制。我们在这里描述了遗传编码的FoxO1传感器的合理发展，该传感器可作为胰岛素生长因子-磷脂酰肌醇3-激酶IGF-PI3K-AKT信号通路活性的下游读数。借助该报道者，我们追踪了单个细胞对多种IGF-I剂量，途径抑制剂和重复治疗的反应。我们观察到单个细胞可以区分多种IGF-I剂量，并且这些反应会随着时间的推移而持续，在单细胞水平上是可重现的，并显示单元间异质性。这些研究暗示信号应答中的细胞间变化具有生物学意义，并支持阐明单个细胞水平的细胞信号传导机制的努力。