Dependency of the slime mold development on the cell-cycle position at the onset of starvation

利用诱导良好同步性的方法，分析了盘基网柄藻Ax-2在饥饿开始时的发育与细胞周期之间的关系，特别是在极化细胞团（蛞蝓）形成过程中的分选行为。在细胞周期的不同位置饥饿的细胞表现出不同的发展特点，在进一步的培养。例如，在有丝分裂前和分裂中的细胞被分选到迁移蛞蝓的前柄区，而在G_2期的大部分时间内饥饿的细胞被分选到后前孢子区。细胞聚集和顶端形成的时间进程也有很大的变化，并与细胞周期有关，G_2期晚期饥饿的细胞发育最快。不同的趋化性和凝聚性通常被认为是重要的细胞分选在网骨藻的发展。事实上，在细胞周期的任何特定阶段，在饥饿的细胞中检测到对趋化剂cAMP的趋化能力的显着差异。根据细胞周期的不同，也获得了不同的抗EDTA内聚性，并且在显示更快速聚集的细胞中更强。此外，我们还认为，无论有无营养，Ax-2细胞都能将自身周期提前到G_2期的某一特定点，并从该点进入分化期，这与营养缺乏是一致的。这里提出的细胞周期相关事件的可能意义进行了讨论，特别强调这种生物体的模式形成。

The relationship between the development of Dictyostelium discoideum Ax-2 and the cell cycle at the onset of starvation was analysed with special reference to sorting behaviors during the formation of polarized cell masses (slug), using a method for inducing good synchrony. Cells starved at different cell-cycle positions showed different developmental features during further culture. For example, cells just before mitosis and dividing cells were sorted out into the anterior prestalk zone of migrating slugs, while cells starved during most of the G_2-phase, into the posterior prespore zone. Time courses of cell aggregatiion and tip formation were also found to vary greatly in a cell-cycle-related manner, and cells starved during the late G_2-phase showed the most rapid development. Differential chemotaxis and cohesiveness are generally considered to be important for cell sorting in Dictyostelium development. In fact, remarkable differences in the chemotactic ability to a chemoattactant, cAMP, were detected among cells starved at any particular phase of the cell cycle. EDTA-resistant cohesiveness was also acquired differently depending on the cell cycle, and it was stronger in the cells showing more rapid aggregation. Moreover, it was suggested that Ax-2 cells may advance their own cycle to a particular point in G_2-phase, irrespective of the presence and absence of nutrients, and enter differentiation phase from this point in concert with nutritional deprivation. The possible significance of the cell-cycle-related events presented here is discussed, with special emphasis on the pattern fromation of this organism.