Cell Biology Group, Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545.
Proc Natl Acad Sci U S A. 1983 Aug;80(16):4983-7. doi: 10.1073/pnas.80.16.4983.
Specific cell-cell contact is a major regulatory signal controlling cell differentiation in Dictyostelium discoideum, causing dramatic changes in the developmental program of gene expression. In this report, we focus on the relationships between specific cell-cell contact and the activity of the genes for discoidin I, an endogenous lectin that has been implicated in the cell-cell cohesion process. By performing quantitative RNA dot-hybridization assays and RNA gel blot-hybridization analyses, using as a probe a recombinant plasmid containing a discoidin I cDNA insert, we have measured changes in discoiding I mRNA levels during normal development and in response to specific manipulations of the state of cellular aggregation. Our major findings are as follows. (i) During normal development on filters, there is a close temporal correspondence between the establishment of specific cell-cell contacts and the decline in discoidin I mRNA levels. By the tight-aggregate stage, discoidin I mRNA is barely detectable. (ii) When tight aggregates are disaggregated and the cells are maintained in the disaggregated state, there is a dramatic rise in discoidin I mRNA content. (iii) When cells are developed in suspension (conditions that interfere with the establishment of tight cell-cell contacts), discoidin I mRNA accumulates to abnormally high levels, and these persist well after the levels in filter-developed cells have declined. Taken together, these results strongly suggest that cell-cell contact is the normal developmental signal to deactivate discoidin I gene expression; thus, a contact-deactivated gene for which a recombinant DNA probe is available has now been identified. Furthermore, we demonstrate that exogenous cAMP almost completely blocks the disaggregation-induced reactivation of discoidin I gene expression. Possible mechanistic relationships between specific cell-cell contact, intracellular cAMP levels, and developmental gene expression are discussed.
特定的细胞-细胞接触是控制盘基网柄菌细胞分化的主要调节信号，导致基因表达的发育程序发生剧烈变化。在本报告中，我们重点研究特定的细胞-细胞接触与内源性凝集素盘菌素 I 基因活性之间的关系，该凝集素与细胞-细胞黏附过程有关。通过进行定量 RNA 斑点杂交分析和 RNA 凝胶印迹杂交分析，使用含有盘菌素 I cDNA 插入片段的重组质粒作为探针，我们测量了正常发育过程中和特定细胞聚集状态操作过程中盘菌素 I mRNA 水平的变化。我们的主要发现如下。（i）在过滤培养物上的正常发育过程中，特定的细胞-细胞接触的建立与盘菌素 I mRNA 水平的下降之间存在密切的时间对应关系。在紧密聚集阶段，盘菌素 I mRNA 几乎无法检测到。（ii）当紧密聚集物被解聚并且细胞保持在解聚状态时，盘菌素 I mRNA 含量急剧上升。（iii）当细胞在悬浮状态下发育（干扰紧密细胞-细胞接触建立的条件）时，盘菌素 I mRNA 积累到异常高的水平，并且在过滤培养物中细胞的水平下降后，这些水平仍然保持很高。综上所述，这些结果强烈表明细胞-细胞接触是使盘菌素 I 基因表达失活的正常发育信号；因此，现在已经鉴定出一个具有重组 DNA 探针的接触失活基因。此外，我们证明外源性 cAMP 几乎完全阻止了解聚诱导的盘菌素 I 基因表达的再激活。特定的细胞-细胞接触、细胞内 cAMP 水平和发育基因表达之间可能存在的机制关系进行了讨论。
