Varnum B, Soll D R
Differentiation. 1981;18(3):151-60. doi: 10.1111/j.1432-0436.1981.tb01116.x.
Chemoresponsiveness to cAMP and to folic acid are monitored in growing, developing, and dedifferentiating amebae of the cellular slime mold Dictyostelium discoideum. Two semiquantitative assays are employed, one measuring the directed movement of cells up a gradient of chemoattractant ('chemotaxis' assay) and the other measuring the outward spreading of cells in response to a chemical stimulant distributed equally throughout the substratum ('spreading' assay). Vegetative amebae possess relatively insignificant levels of chemotactic responsiveness to cAMP. Six h after the initiation of development, at approximately the same time as the onset of aggregation, cells rapidly acquire chemotactic responsiveness to cAMP. During 'erasure', a dedifferentiation induced by resuspending aggregating cells in fresh nutrient medium, chemotactic responsiveness to cAMP is lost just after the erasure event. By the same chemotactic assay, it is demonstrated that vegetative amebae possess a significant level of chemotactic responsiveness to folic acid. Two h after the initiation of development, cells completely lose chemotactic responsiveness to folic acid. During erasure, cells reacquire chemotactic responsiveness to folic acid at approximately the same time that they lose responsiveness to cAMP. Dramatically different results are obtained by the spreading assay. When cells lose chemotactic responsiveness to folic acid early in development and when erasing cells lose chemotactic responsiveness to cAMP, they retain the spreading response to the two stimulants, respectively. The different results obtained for chemoreception employing the two assays are discussed in terms of molecular mechanisms, and a testable hypothesis is proposed for the possible roles of chemoresponsiveness and erasure in late morphogenesis.
在细胞黏菌盘基网柄菌生长、发育和去分化的变形虫中监测对环磷酸腺苷（cAMP）和叶酸的化学响应性。采用了两种半定量测定法，一种测量细胞在趋化因子梯度上的定向运动（“趋化性”测定法），另一种测量细胞在整个基质中均匀分布的化学刺激物作用下的向外扩散（“扩散”测定法）。营养型变形虫对cAMP的趋化反应水平相对较低。发育开始6小时后，大约在聚集开始的同时，细胞迅速获得对cAMP的趋化反应性。在“消除”过程中，即将聚集的细胞重悬于新鲜营养培养基中诱导的去分化过程中，对cAMP的趋化反应性在消除事件后立即丧失。通过相同的趋化性测定法表明，营养型变形虫对叶酸具有显著水平的趋化反应性。发育开始2小时后，细胞完全丧失对叶酸的趋化反应性。在消除过程中，细胞在丧失对cAMP反应性的大致同时重新获得对叶酸的趋化反应性。通过扩散测定法获得了截然不同的结果。当细胞在发育早期丧失对叶酸的趋化反应性以及去分化细胞丧失对cAMP的趋化反应性时，它们分别保留对这两种刺激物的扩散反应。从分子机制方面讨论了采用这两种测定法进行化学感受所获得的不同结果，并针对化学响应性和消除在后期形态发生中的可能作用提出了一个可检验的假设。
