Clarke M, Gomer R H
Oklahoma Medical Research Foundation, Program in Molecular and Cell Biology, Oklahoma City 73104, USA.
Experientia. 1995 Dec 18;51(12):1124-34. doi: 10.1007/BF01944730.
Throughout growth and development, Dictyostelium cells secrete autocrine factors that accumulate in proportion to cell density. At sufficient concentration, these factors cause changes in gene expression. Vegetative Dictyostelium cells continuously secrete prestarvation factor (PSF). The bacteria upon which the cells feed inhibit their response to PSF, allowing the cells to monitor their own density in relation to that of their food supply. At high PSF/bacteria ratios, which occur during late exponential growth, PSF induces the expression of several genes whose products are needed for cell aggregation. When the food supply has been depleted, PSF production declines, and a second density-sensing pathway is activated. Starving cells secrete conditioned medium factor (CMF), a glycoprotein of Mr 80 kDa that is essential for the development of differentiated cell types. Antisense mutagenesis has shown that cells lacking CMF cannot aggregate, and preliminary data suggest that CMF regulates cAMP signal transduction. Calculations indicate that a mechanism of simultaneously secreting and recognizing a signal molecule, as used by Dictyostelium to monitor cell density, could also be used to determine the total number of cells in a tissue.
在整个生长和发育过程中，盘基网柄菌细胞分泌自分泌因子，其积累量与细胞密度成正比。在足够的浓度下，这些因子会导致基因表达发生变化。营养期的盘基网柄菌细胞持续分泌饥饿前因子（PSF）。细胞所摄取的细菌会抑制它们对PSF的反应，从而使细胞能够相对于食物供应来监测自身密度。在指数生长后期出现的高PSF/细菌比率下，PSF会诱导几种基因的表达，这些基因的产物是细胞聚集所必需的。当食物供应耗尽时，PSF的产生会下降，并且会激活第二条密度感应途径。饥饿的细胞会分泌条件培养基因子（CMF），这是一种分子量为80 kDa的糖蛋白，对于分化细胞类型的发育至关重要。反义诱变表明，缺乏CMF的细胞无法聚集，初步数据表明CMF调节cAMP信号转导。计算表明，盘基网柄菌用于监测细胞密度的同时分泌和识别信号分子的机制，也可用于确定组织中的细胞总数。
