Waddell D R
J Embryol Exp Morphol. 1982 Aug;70:75-98.
The spatial pattern of aggregation centres of the slime mould Dictyostelium discoideum was analysed by using nearest-neighbour distributions. Both undisturbed cultures, and cultures that were initiated from cells dissociated from cultures that had already aggregated, formed non-randomly spaced patterns. However, the minimal distance between aggregates in undisturbed cultures was approximately ten times that observed in dissociated cultures. In undisturbed cultures the aggregate size is regulated as a function of cell density (Bonner + Hoffman, 1963): as cell density increases aggregate density decreases and the aggregate size consequently increases. At the same cell density more and smaller aggregates were formed by dissociated cultures than by undisturbed cultures. Nevertheless, the same cell-density-dependent regulation of aggregate density existed in the dissociated cultures. Here a model is developed to account for both the non-random spacing and the cell-density-dependent regulation of aggregate density. In this model, distance-dependent competition occurs between points in a random prepattern to generate patterns very similar to those observed in experiments. The cell-density-dependent regulation of the aggregate density can be explained by assuming that a constant fraction of the cell population has the capacity to initiate centres at the time of pattern determination regardless of the cell density. As the cell density is increased the fraction of potential centres that survive distance-dependent competition decreases and hence the aggregate size increases. These results suggest that distance-dependent competition may be a mechanism that evolved to control aggregate size at high cell densities. Results obtained with this model indicate that the decrease in aggregate size in dissociated cultures is due primarily to an increase in the fraction of the cell population capable of initiating centres. This implies that as morphogenesis progresses a greater fraction of the cell population acquire a capacity which they will not normally express. Although this increase may have a function in later stages of morphogenesis, it may also provide a way to ensure aggregation in small populations of amoebae and at low cell densities.
通过使用最近邻分布分析了黏菌盘基网柄菌聚集中心的空间模式。未受干扰的培养物以及由已聚集培养物中解离的细胞起始的培养物，均形成了非随机间隔的模式。然而，未受干扰的培养物中聚集体之间的最小距离约为解离培养物中观察到的距离的十倍。在未受干扰的培养物中，聚集体大小作为细胞密度的函数受到调节（邦纳和霍夫曼，1963年）：随着细胞密度增加，聚集体密度降低，聚集体大小相应增加。在相同细胞密度下，解离培养物比未受干扰的培养物形成更多更小的聚集体。尽管如此，解离培养物中同样存在细胞密度依赖性的聚集体密度调节。在此开发了一个模型来解释聚集体密度的非随机间隔和细胞密度依赖性调节。在该模型中，随机预模式中的点之间发生距离依赖性竞争，以生成与实验中观察到的模式非常相似的模式。聚集体密度的细胞密度依赖性调节可以通过假设在模式确定时，无论细胞密度如何，恒定比例的细胞群体具有启动中心的能力来解释。随着细胞密度增加，在距离依赖性竞争中存活的潜在中心的比例降低，因此聚集体大小增加。这些结果表明，距离依赖性竞争可能是一种在高细胞密度下进化以控制聚集体大小的机制。用该模型获得的结果表明，解离培养物中聚集体大小的减小主要是由于能够启动中心的细胞群体比例增加。这意味着随着形态发生的进展，更大比例的细胞群体获得了一种它们通常不会表达的能力。尽管这种增加可能在形态发生的后期阶段具有功能，但它也可能提供一种确保在小群体变形虫和低细胞密度下聚集的方法。
