So J S, Weeks G
Department of Microbiology, University of British Columbia, Vancouver, Canada.
Differentiation. 1994 May;56(3):131-5. doi: 10.1046/j.1432-0436.1994.5630131.x.
An earlier finding that the ecmA and ecmB prestalk cell specific genes exhibited very different responses to cyclic AMP prompted the suggestion that cyclic AMP might act as the major spatial regulator of the prestalk cell developmental pattern in Dictyostelium. A more detailed kinetic analysis in monolayers of Dictyostelium has revealed that cyclic AMP inhibits the rate of expression of all three differentiation inducing factor (DIF) inducible genes, ecmA, ecmB and pDd26. After prolonged incubation, however, cyclic AMP enhances the levels of both ecmA and ecmB mRNAs, and nuclear run-on experiments suggest that cyclic AMP inhibits the degradation of both mRNA species. This complex response to cyclic AMP can explain the differential effects reported previously. Thus depending upon the experimental conditions, cyclic AMP can either enhance or reduce the apparent steady state level of a specific mRNA species. These results are not compatible with the earlier proposal that cyclic AMP is a spatial regulator of the prestalk developmental pattern. Although ecmA and ecmB accumulate rapidly in response to DIF, there is a lag in the accumulation of pD26 mRNA and the induction requires protein synthesis. These results suggest that pDd26 transcription requires the accumulation of an additional factor(s). Inhibition of pDd26 mRNA accumulation by cyclic AMP also occurs during the lag period, suggesting the possibility that cyclic AMP inhibits the accumulation of the, as yet, unknown factor. The inhibitory effect of cyclic AMP on pDd26 gene expression is unaffected by caffeine, suggesting that inhibition does not involve adenylate cyclase activation.(ABSTRACT TRUNCATED AT 250 WORDS)
一项较早的发现表明，ecmA和ecmB前柄细胞特异性基因对环磷酸腺苷（cAMP）表现出非常不同的反应，这提示cAMP可能是盘基网柄菌前柄细胞发育模式的主要空间调节因子。对盘基网柄菌单层细胞进行的更详细的动力学分析显示，cAMP会抑制所有三种分化诱导因子（DIF）诱导型基因ecmA、ecmB和pDd26的表达速率。然而，长时间孵育后，cAMP会提高ecmA和ecmB的mRNA水平，并且细胞核转录实验表明cAMP抑制这两种mRNA的降解。对cAMP的这种复杂反应可以解释先前报道的不同效应。因此，根据实验条件，cAMP可以增强或降低特定mRNA的表观稳态水平。这些结果与之前提出的cAMP是前柄发育模式的空间调节因子的观点不一致。虽然ecmA和ecmB会迅速响应DIF而积累，但pD26 mRNA的积累存在滞后，且诱导需要蛋白质合成。这些结果表明pDd26转录需要额外一种或多种因子的积累。cAMP对pDd26 mRNA积累的抑制也发生在滞后阶段，这表明cAMP可能抑制了这种未知因子的积累。cAMP对pDd26基因表达的抑制作用不受咖啡因影响，这表明抑制作用不涉及腺苷酸环化酶的激活。（摘要截选至250词）
