Molecular biological studies on differentiation of slime mold cells

1.同质粘菌细胞的聚集导致两种细胞(前孢子和前柄)的分化，这两种细胞分别成为子实体的备用细胞和柄细胞。为了分离在假定细胞分化过程中特异表达的基因，分离了与富含在前孢子和前柄细胞中的mRNAs互补的DNA克隆，并从中获得了几个基因组DNA克隆。其中一些基因在任一类型的细胞中选择性转录，而另一些基因在早期阶段表达，并在两种类型的细胞中转录。后者在一种细胞类型中变得丰富的事实是由于它们在另一种细胞类型中不稳定造成的。当含有两个前孢子特异基因5‘上游区的DNA片段转化粘菌细胞时，它们在特定发育阶段和一种网状细胞类型中特异表达。负责反式…调控的DNA序列目前正在鉴定更多的基因克隆，并分离出与这些序列结合的核蛋白。网柄网柄菌质粒的全序列。已被披露。结论：1.用该载体转化盘状芽孢杆菌细胞时，其表达开始于聚集期，并受外源cAMP诱导。发现了分离的细胞在不形成组织的情况下分化的条件，其中细胞分化成孢子和柄细胞是由细胞外pH控制的。我们成功地测定了细胞内钙离子浓度，发现加入cAMP后，聚集细胞内的钙离子浓度增加了4倍。提示钙离子参与了细胞趋化反应的信号转导。细胞黏附分子GP80的一部分糖链可能与细胞黏附有关。在有性繁殖过程中(大囊泡形成)，细胞合成不同于无性繁殖(子实体形成)过程中产生的蛋白质，两种交配型细胞表面存在的两种糖蛋白GP138和70被确定为参与有性细胞融合的候选分子。较少

1. Aggregation of homogenous slime mold cells leads to differentiation of two types of cells (prespore and prestalk) which become spares and stalk cells respectively of the fruiting body. To isolate genes which are specifically expressed during differentiation of the presumptive cells, clones of DNA complementary to mRNAs enriched in prespore and prestalk cells were isolated, from which several genomic DNA clones were obtained. Some of these genes were selctively transcribed in either type of cells, while the others were expressed from the earlier stages and transcribed in both cell types. The fact that the latter mRNAs become enriched in one cell type was resulted from their destabilization in the other cell type. When slime mold cells were transformed by DNA fragments containing the 5' upstream regions of two prespore specific genes, they were specifically expressed at certain developmental stages and in a perticular cell type. The sequences of DNA responsible for requlation of trans … More cription of the genes are being identified and nuclear proteins binding to such sequences being isolated. The entire sequence of a plasmid contained in Dictyostelium sp. was disclosed. when D. discoideum cells were transformed by the plasmid, its expression began at the aggregation stage and was induced by exogenous cAMP.2. The conditions under which cells as isolated differentiate without forming a tissue were found, where differentiation of cells into spores and stalk cell was controlled by extracellular pH. We succeded in determining cytosolic Ca^<++> concentration and found that upon addition of cAMP it increased 4 times in aggregating cells. This suggests the involvement of Ca^<++> in signal transduction of chemotactic response of the cells. A part of the sugar chains of the cell adhesion molecule GP80 was likely to be responsible for cell adhesion. During the process of sexual reproduction (macrocyst formation), cells synthesize different kind of proteins from those made during asexual reproduction (fruiting body formation) and two glycoproteins, GP138 and 70, present on the surface both mating type cells were identified as the candidates of molecules involved in the sexual cell fusion. Less