Regulation of differentiation in slime mold cells

在细胞黏菌的发育过程中，细胞聚集形成组织，其中前部和后部分别分化出两种类型的细胞（前柄和前孢子）。为了阐明分化的调控机制，我们进行了以下研究。细胞生长与分化的关系细胞在组织中分化为前茎细胞还是前孢子细胞与饥饿时的细胞周期阶段有关。确定了从生长到分化的推定转移点（PS），并检测了该点特异性表达的基因。鉴定出3种基因（Quit 1、Quit 2、Quit 3）。Quit基因编码cAMP受体CAR1和新型钙结合蛋白Quit2。细胞在发育过程中分泌一种诱导茎细胞分化的因子（STIF）。STIF被8-溴- camp取代的事实表明，STIF通过蛋白激酶A （PKA）起作用。这种可能性得到了证实，用PKA显性阴性抑制剂转化的细胞不能形成茎细胞。STIF可激活茎特异性ecmB基因，但不能激活ecmA基因。利用转染了各种缺失基因的细胞鉴定了STTF作用的ecmB启动子上游区域。map -激酶在信号转导中的作用。对无聚集突变体的分析表明，map -激酶ERK2基因在细胞趋化性中起重要作用。ERK2通过膜受体CAR1和CAR3被细胞外cAMP激活，最终激活腺苷酸环化酶（AC），而不涉及异三量g蛋白。AC的激活导致细胞cAMP的增加，进而使ERK2失活。在营养期，ERK2的激活对细胞生长至关重要，它由叶酸引起，强烈依赖于G蛋白。

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, respectively.To elucidate regulatory mechanisms of differentiation, we made the following studies.1.Relation of cell growth and differentiationWhether cells differentiate into either prestalk or prespore cells in the tissue is related to the cell cycle phase at the time of starvation.Putative shift (PS) point from growth to differentiation was determined and genes specifically expressed at the point were examined.Three kinds of genes (Quit 1,2,3) were identified.The Quit gene encodes a cAMP receptor, CAR1 and the Quit2 a new type of calcium-binding protein (CAF-1).2.Mechanism of stalk cell-inducing factorCells secrete during development a factor inducing stalk cell differentiation (STIF).The fact that STIF is replaced by 8-bromo-cAMP suggests that STIF acts through protein kinase A (PKA).This possibility was verified, as cells transformed with a dominant negative inhibitor of PKA was incapable of stalk cell formation.STIF activates stalk-specific ecmB gene, but not ecmA gene.The upstream region of ecmB promoter where STTF acts was identified by using cells transformed with various deleted genes.3.Role of MAP-kinase in signal transduction.Analysis of an aggregateless mutant indicated a MAP-kinase, ERK2 gene has an important role in chemotaxis of cells.ERK2 was activated by extracellular cAMP through membrane receptors, CAR1 and CAR3 and eventually activates adenylate cyclase (AC), without involving heterotrimetric G-proteins.Activation of AC results in an increase in cellular cAMP which in turn inactivates ERK2.Activation of ERK2 is essential for cell growth during the vegetative phase, which is brought about by folic acid and strongly depends on the G proteins.