标题： 单细胞直接梯度感应的准确性 显示英文标题

标题： Accuracy of direct gradient sensing by single cells

摘要： 许多类型的细胞能够准确感知其直径上的化学物质的微弱梯度，使细胞能够向化学源移动或远离。这种趋化能力依赖于细胞从通过扩散到达细胞表面受体的随机粒子中推断梯度的非凡能力。尽管已经探索了细胞浓度感知的物理极限，但尚无关于梯度感知物理极限的理论。在这里，我们使用一个完全吸收球和一个完全监测球作为模型，分别从吸收的表面粒子密度或球形体积内自由扩散粒子的位置推断梯度，推导出这样的理论。我们发现，完全吸收球在浓度和梯度感知方面都优于完全监测球，因为之前观察到的粒子不会被重新测量。吸收球的优势有助于解释细胞表面上存在信号降解酶的现象，例如在黏菌（Dictyostelium discoideum，简称Dicty）中用于降解cAMP的PDE，以及在酿酒酵母（Saccharomyces cerevisiae，简称budding yeast）中用于降解α交配因子的BAR1。定量上，我们的理论与最近对Dicty沿cAMP梯度移动的测量结果相符，表明这些细胞在梯度检测的物理极限附近运行。 显示英文摘要

摘要： Many types of cells are able to accurately sense shallow gradients of chemicals across their diameters, allowing the cells to move towards or away from chemical sources. This chemotactic ability relies on the remarkable capacity of cells to infer gradients from particles randomly arriving at cell-surface receptors by diffusion. Whereas the physical limits of concentration sensing by cells have been explored, there is no theory for the physical limits of gradient sensing. Here, we derive such a theory, using as models a perfectly absorbing sphere and a perfectly monitoring sphere, which, respectively, infer gradients from the absorbed surface particle density or the positions of freely diffusing particles inside a spherical volume. We find that the perfectly absorbing sphere is superior to the perfectly monitoring sphere, both for concentration and gradient sensing, since previously observed particles are never remeasured. The superiority of the absorbing sphere helps explain the presence at the surfaces of cells of signal degrading enzymes, such as PDE for cAMP in Dictyostelium discoideum (Dicty) and BAR1 for mating factor alpha in Saccharomyces cerevisiae (budding yeast). Quantitatively, our theory compares favorably to recent measurements of Dicty moving up a cAMP gradient, suggesting these cells operate near the physical limits of gradient detection.