Szüts D, Eresh S, Bienz M
Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge CB2 2QH, UK.
Genes Dev. 1998 Jul 1;12(13):2022-35. doi: 10.1101/gad.12.13.2022.
Endoderm induction in Drosophila is mediated by the extracellular signals Decapentaplegic (Dpp) and Wingless (Wg). We discovered a secondary signal with a permissive role in this process, namely Vein, a neuregulin-like ligand that stimulates the epidermal growth factor receptor (EGFR) and Ras signaling. Dpp and Wg up-regulate vein expression in the midgut mesoderm in two regions overlapping the Dpp sources. Experiments based on lack of function and ectopic stimulation of Dpp and EGFR signaling show that these two pathways are functionally interdependent and that they synergize with each other, revealing functional intertwining. The transcriptional response elements for the Dpp signal in midgut enhancers from homeotic target genes are bipartite, comprising CRE sites as well as binding sites for the Dpp signal-transducing protein Mad. Of these sites, the CRE seems to function primarily in the response to Ras, the secondary signal of Dpp. We discuss the potential significance of why an inductive process might use a secondary signal whose function is intertwined with that of the primary signal.
果蝇中内胚层的诱导是由细胞外信号“五体不全”（Dpp）和“无翅”（Wg）介导的。我们发现了在此过程中起许可作用的第二种信号，即Vein，一种刺激表皮生长因子受体（EGFR）和Ras信号传导的类神经调节蛋白配体。Dpp和Wg在与Dpp来源重叠的两个区域中上调中肠中胚层的vein表达。基于功能缺失和对Dpp与EGFR信号传导进行异位刺激的实验表明，这两条信号通路在功能上相互依赖且相互协同，揭示了功能上的交织。来自同源异型靶基因的中肠增强子中Dpp信号的转录反应元件是二分的，包括CRE位点以及Dpp信号转导蛋白Mad的结合位点。在这些位点中，CRE似乎主要在对Dpp的次级信号Ras的反应中发挥作用。我们讨论了为什么诱导过程可能会使用一种功能与主要信号交织在一起的次级信号的潜在意义。
