Cell differentiation and pattern formation in a cell-cycle dependent manner in slime mold cells

以β-半乳糖苷酶为细胞标记物，采用变温同步化方法，分析了盘基网柄藻Ax-2细胞在饥饿条件下的分选速率及其与细胞周期的关系。细胞（T7）饥饿之前的PS-点，从细胞进入分化阶段时，饥饿聚集最迅速，可能作为聚集中心，但最终分选出的后区的迁移蛞蝓。与此相反，T1细胞饥饿后PS点表现出较慢的聚集与T7细胞相比。在进一步培养过程中，T1细胞被分选到尖端聚集体的顶端，并主要位于迁移蛞蝓的前区，利用差异噬斑杂交技术分析了细胞从增殖到分化的迁移过程中相关基因的表达。结果，Quit 1被克隆为一个在PS点前饥饿细胞时特异表达的基因。Quit 1基因的编码区与cAMP受体1基因的编码区完全相同，是发育所必需的。Quit 1 mRNA在PS点附近的细胞饥饿后不表达，从而表明cAMP受体1对细胞分化的重要性以及PS点的实际存在。

The sorting behaver of Dictyostelium discoideum Ax-2 cells and its relation to the cell-cycle phase at the onset of starvation were analyzed with reference to pattern formation, using beta-galactosidase as a cell maker and the temperature shift method for cell synchronization. Cells (T7) starved just before the PS-point from which cells enter the differentiation phase when starved aggregated most rapidly and possibly functioned as aggregation centers, but were eventurally sorted out to the posterior zone of migrating slugs. In contrast, T1 cells starved just after the PS-point exhibited slower aggregation compared with T7 cells. During further culture, T1 cells then sorted out to the apical tips of tipped aggregates and were located predominantly in the anterior zone of migrating slugs.The gene expressions associated with the swotchover from cell proliferation to differentiation were also analyzed using the differential plaque hybridization. As a result, Quit1 was cloned as a specifically expressed gene when cells were starved just beforethe PS-point. The coding region of Quit1 gene was identical with that of the cAMP recepter 1 gene, which is essential for development. The Quit1 mRNA was asecifically expressed just after starvation of cells around the PS-point, thus indicating the importance of the cAMP recepter 1 for cellular differentiation as well as the actual existence of the PS-point.