Department of Biology, ILSB MS 3474, Texas A&M University, College Station, Texas 77843-3474, USA.
Dev Growth Differ. 2011 May;53(4):482-94. doi: 10.1111/j.1440-169X.2010.01248.x. Epub 2011 Apr 27.
The social amoeba Dictyostelium discoideum is one of the leading model systems used to study how cells count themselves to determine the number and/or density of cells. In this review, we describe work on three different cell-density sensing systems used by Dictyostelium. The first involves a negative feedback loop in which two secreted signals inhibit cell proliferation during the growth phase. As the cell density increases, the concentrations of the secreted factors concomitantly increase, allowing the cells to sense their density. The two signals act as message authenticators for each other, and the existence of two different signals that require each other for activity may explain why previous efforts to identify autocrine proliferation-inhibiting signals in higher eukaryotes have generally failed. The second system involves a signal made by growing cells that is secreted only when they starve. This then allows cells to sense the density of just the starving cells, and is an example of a mechanism that allows cells in a tissue to sense the density of one specific cell type. The third cell density counting system involves cells in aggregation streams secreting a signal that limits the size of fruiting bodies. Computer simulations predicted, and experiments then showed, that the factor increases random cell motility and decreases cell-cell adhesion to cause streams to break up if there are too many cells in the stream. Together, studies on Dictyostelium cell density counting systems will help elucidate how higher eukaryotes regulate the size and composition of tissues.
团聚生境阿米巴（Dictyostelium discoideum）是用于研究细胞如何自我计数以确定细胞数量和/或密度的主要模型系统之一。在这篇综述中，我们描述了团聚生境阿米巴使用的三种不同的细胞密度感应系统。第一种系统涉及负反馈回路，其中两种分泌信号在生长阶段抑制细胞增殖。随着细胞密度的增加，分泌因子的浓度也随之增加，使细胞能够感知其密度。这两种信号彼此充当消息验证器，而两种需要彼此才能发挥活性的不同信号可能解释了为什么以前在高等真核生物中识别自分泌增殖抑制信号的努力通常都失败了。第二种系统涉及生长细胞分泌的信号，只有在饥饿时才会分泌。这使得细胞能够仅感知饥饿细胞的密度，这是一种允许组织中的细胞感知一种特定细胞类型密度的机制的例子。第三种细胞密度计数系统涉及聚集流中的细胞分泌一种限制子实体大小的信号。计算机模拟预测，然后实验表明，如果流中有太多细胞，该因子会增加随机细胞运动并降低细胞间的粘附，从而导致流中断。团聚生境阿米巴细胞密度计数系统的研究将有助于阐明高等真核生物如何调节组织的大小和组成。
