Feit I N, Bonner J T, Suthers H B
Department of Biology, Franklin and Marshall College, Lancaster, PA 17604.
Dev Genet. 1990;11(5-6):442-6. doi: 10.1002/dvg.1020110519.
Ammonia appears to be an important regulatory signal for several aspects of the Dictyostelium life cycle. The postulated role of ammonia in the determination of the prespore pathway in cells of the slug stage has led us to examine the effect of ammonia on the prestalk/prespore ratio of migrating slugs. In the presence of 10(-3) M ammonium chloride, the volume of the prestalk region decreases by 40.8%. The kinetics of the process make it unlikely that this is due to a shift in the differentiation pathway. A test of the hypothesis that the decrease in volume of the prestalk region is due to the conversion of prestalk cells to anterior-like cells shows that the percent of anterior-like cells in the posterior region increases by the amount predicted by the hypothesis. This suggests that ammonia may be the molecular signal, produced by the tip, that prevents anterior-like cells from chemotactically migrating to the tip and thereby becoming anterior cells. The effect of enzymatic removal of ammonia from vitally stained migrating slugs is the appearance of a series of dark stripes beginning at the posterior end and progressing forward. We interpret this as a result of progressive removal of anterior-like cells from tip dominance and essentially as the formation of new potential tips. Indeed, in a few cases one or even two of the stripes separate from the posterior of the cell mass and form small fruiting bodies. We consider the phenomenon of stripe formation further evidence that the tip acts on anterior-like cells through ammonia.
氨似乎是盘基网柄菌生命周期多个方面的重要调节信号。氨在蛞蝓阶段细胞中前孢子途径决定过程中的假定作用，促使我们研究氨对迁移中蛞蝓前柄细胞/前孢子细胞比例的影响。在10⁻³ M氯化铵存在的情况下，前柄区域的体积减少了40.8%。该过程的动力学表明，这不太可能是由于分化途径的转变。关于前柄区域体积减少是由于前柄细胞转化为类似前端细胞的假设的测试表明，后部区域中类似前端细胞的百分比按该假设预测的数量增加。这表明氨可能是由前端产生的分子信号，它阻止类似前端细胞通过趋化作用迁移到前端，从而使其不会变成前端细胞。对经活体染色的迁移中蛞蝓进行酶促去除氨的处理后，会出现一系列从后端开始并向前推进的深色条纹。我们将此解释为类似前端细胞逐渐摆脱前端优势的结果，本质上是新潜在前端的形成。实际上，在少数情况下，其中一条甚至两条条纹会从细胞团块的后部分离出来，形成小的子实体。我们认为条纹形成现象进一步证明了前端通过氨作用于类似前端细胞。
