Jiang J, Levine M
Department of Biology, University of California, San Diego, La Jolla 92093-0322.
Cell. 1993 Mar 12;72(5):741-52. doi: 10.1016/0092-8674(93)90402-c.
The dorsal (dl) morphogen gradient initiates the formation of the mesoderm, neuroectoderm, and dorsal ectoderm by setting different limits of regulatory gene expression along the dorsoventral axis of the early Drosophila embryo. In this paper, we show that low affinity dl-binding sites restrict target gene expression to the ventralmost regions (presumptive mesoderm), where there are peak levels of dl, while high affinity sites permit expression in ventrolateral regions (mesoderm and mesectoderm) containing intermediate levels of the morphogen. Activation by low levels of dl in lateral regions (the presumptive neuroectoderm) depends on cooperative DNA binding interactions between dl and bHLH proteins. The snail repressor blocks this interaction and restricts expression to the neuroectoderm. We discuss how enhancers serve as templates to bring weakly interacting regulatory factors into close proximity so that they can function combinatorially to activate and repress transcription.
背侧（dl）形态发生素梯度通过在早期果蝇胚胎的背腹轴上设定调节基因表达的不同界限，启动中胚层、神经外胚层和背侧外胚层的形成。在本文中，我们表明低亲和力的dl结合位点将靶基因表达限制在dl水平最高的最腹侧区域（假定的中胚层），而高亲和力位点允许在含有中等水平形态发生素的腹外侧区域（中胚层和中胚层ectoderm）表达。外侧区域（假定的神经外胚层）中低水平的dl激活取决于dl与bHLH蛋白之间的协同DNA结合相互作用。蜗牛阻遏物阻断这种相互作用，并将表达限制在神经外胚层。我们讨论了增强子如何作为模板，使弱相互作用的调节因子紧密靠近，从而使它们能够组合发挥作用，激活和抑制转录。
