Jermyn K, Wiliams J
MRC Laboratory for Molecular Cell Biology, University College London, UK.
Differentiation. 1995 Apr;58(4):261-7. doi: 10.1046/j.1432-0436.1995.5840261.x.
The Dictyostelium ras gene, rasD, encodes an mRNA that is more abundant in prestalk than prespore cells in the migratory slug. Its expression is inducible by extracellular cAMP but is not inducible by the prestalk and stalk cell morphogen differentiation inducing factor (DIF). We show that a rasD-lacZ fusion gene is first expressed in approximately one half of the cells in the aggregate, including some cells that also express a prespore-specific marker. The amount of rasD-lacZ fusion protein in prespore cells then diminishes as the slug is formed. Analysis of a rasD-lacZ fusion protein with an N terminal substitution that reduces protein stability within the cell provides strong confirmatory evidence that the ras gene product becomes enriched in prestalk cells by selective repression of gene expression in prespore cells. In contrast, the DIF-inducible ecmA gene is expressed only in those cells that will become prestalk cells in the migratory slug. These results show that there are two different ways in which an mRNA may become enriched in prestalk cells and support the view that DIF is the inducer of prestalk cell differentiation.
盘基网柄菌的ras基因rasD编码一种mRNA，在迁移期蛞蝓中，其在前柄细胞中的丰度高于前孢子细胞。其表达可被细胞外cAMP诱导，但不能被前柄和柄细胞形态发生分化诱导因子（DIF）诱导。我们发现，rasD-lacZ融合基因首先在聚集物中约一半的细胞中表达，包括一些也表达前孢子特异性标记的细胞。随着蛞蝓的形成，前孢子细胞中rasD-lacZ融合蛋白的量随后减少。对具有N端替代的rasD-lacZ融合蛋白进行分析，该替代降低了细胞内蛋白质的稳定性，提供了有力的证实证据，即ras基因产物通过选择性抑制前孢子细胞中的基因表达而在前柄细胞中富集。相比之下，DIF诱导的ecmA基因仅在迁移期蛞蝓中那些将成为前柄细胞的细胞中表达。这些结果表明，mRNA在前柄细胞中富集有两种不同的方式，并支持DIF是前柄细胞分化诱导剂的观点。
