Regulation of gene expression during cell differentiation in the cellular slime molds

在细胞黏菌的发育过程中，细胞聚集形成组织，在组织的前部和后部分化出两种类型的细胞（前柄和前孢子）。为了阐明细胞分化和模式形成的机制，我们进行了以下研究。(1)我们已经证明，在滚轴管中培养的细胞在液体中形成一个凝集体，其中前柄细胞和前孢子细胞表现出明确的分化模式，而不经历形态发生。Williams进行了类似的细胞培养，其茎前特异性ecmA和ecmB基因的表达可以通过bata -半乳糖苷酶活性进行组织化学检测。在凝集物中，表达ecmA的细胞先随机出现，然后聚集到中心，表达ecmB的细胞出现在表层。这一结果与之前用孢子前分化模式得到的结果一致，表明分化模式是通过对分化细胞的分选而调整的。(2)前期研究表明，孢子前特异性Dp87基因-442 ~ -349 bp上游区域对其表达具有重要意义。当该区域与黏菌肌动蛋白基因的基启动子融合后，嵌合体基因在营养期开始表达，在前柄细胞和前孢子细胞之间表达无差异。这表明上游区域只增加转录量，但细胞类型和发育特异性表达受-349 bp以下区域的调控。(3)利用Dp87启动子与bata -半乳糖苷酶基因融合转化细胞，检测Dp87基因在正常发育过程中的表达情况。表达Dp87的细胞首先随机出现在聚集流中，随后聚集在聚集中心的基部，延续了上述分化模式是通过分化细胞的分选而形成的观点。

In the development of cellular slime molds, cells aggregate to form a tissue, in which two types of cells (prestalk and prespore) differentiate in the anterior and the posterior parts. To elucidate the mechanisms of cell differentiation and pattem formation, we made the following studies.(1) We have shown that cells cultured in liquid in a roller tube form an agglutinate in which prestalk, and prespore cells exhibit a definite pattern of differentiation without undergoing morphogenesis. Williams made a similar culture of cells whose expression of prestalk-specific ecmA and ecmB genes can be histochemically detected by BATA-galactosidase activity. In the agglutinates forined, cells expressing ecmA first arose randomly and then were collected to the center, while those expressing ecmB appeared on the surface layers. The result is consistent with the previous one obtained with the pattem of prespore differentiation and indicates that the differentiation pattem is tonned by sorting out of differentiated cells.(2) We have previously shown that the upstream region between -442 and -349 bp of presporespecific Dp87 gene is important for its expression. When this region is fused with the basal promoter of slime mold actin gene, the chimera gene was expressed from the vegetative stage and no difference in expression was detected between prestalk and prespore cells. This suggests that the upstream region only enhances the amount of transcription, but that cell-type-and development-specific expression is regulated by the region below -349 bp.(3) Expression of Dp87 gene during normal development was examined by using cells transformed with the promoter of Dp87 fused with BATA-galactosidase gene. Cells expressing Dp87 first appeared randomly in the aggregation streams and were later accumulated in the basal part of the aggregation centers, continuing the above notion that the differentiation pattem is formed by sorting out of differentiated cells.