Langeland J A, Attai S F, Vorwerk K, Carroll S B
Howard Hughes Medical Institute, R. M. Bock Laboratories, University of Wisconsin, Madison 53706, USA.
Development. 1994 Oct;120(10):2945-55. doi: 10.1242/dev.120.10.2945.
We present a genetic and molecular analysis of two hairy (h) pair-rule stripes in order to determine how gradients of gap proteins position adjacent stripes of gene expression in the posterior of Drosophila embryos. We have delimited regulatory sequences critical for the expression of h stripes 5 and 6 to 302 bp and 526 bp fragments, respectively, and assayed the expression of stripe-specific reporter constructs in several gap mutant backgrounds. We demonstrate that posterior stripe boundaries are established by gap protein repressors unique to each stripe: h stripe 5 is repressed by the giant (gt) protein on its posterior border and h stripe 6 is repressed by the hunchback (hb) protein on its posterior border. Interestingly, Krüppel (Kr) limits the anterior expression limits of both stripes and is the only gap gene to do so, indicating that stripes 5 and 6 may be coordinately positioned by the Kr repressor. In contrast to these very similar cases of spatial repression, stripes 5 and 6 appear to be activated by different mechanisms. Stripe 6 is critically dependent upon knirps (kni) for activation, while stripe 5 likely requires a combination of activating proteins (gap and non-gap). To begin a mechanistic understanding of stripe formation, we locate binding sites for the Kr protein in both stripe enhancers. The stripe 6 enhancer contains higher affinity Kr-binding sites than the stripe 5 enhancer, which may allow for the two stripes to be repressed at different Kr protein concentration thresholds. We also demonstrate that the kni activator binds to the stripe 6 enhancer and present evidence for a competitive mechanism of Kr repression of stripe 6.
我们对两条毛状（h）成对规则条纹进行了遗传和分子分析，以确定间隙蛋白梯度如何在果蝇胚胎后部定位相邻的基因表达条纹。我们已将对h条纹5和6表达至关重要的调控序列分别界定为302 bp和526 bp的片段，并在几种间隙突变背景下检测了条纹特异性报告构建体的表达。我们证明，后部条纹边界是由每条条纹特有的间隙蛋白阻遏物建立的：h条纹5在其后边界被巨蛋白（gt）抑制，h条纹6在其后边界被驼背蛋白（hb）抑制。有趣的是，Krüppel（Kr）限制了两条条纹的前部表达界限，并且是唯一这样做的间隙基因，这表明条纹5和6可能由Kr阻遏物协同定位。与这些非常相似的空间抑制情况相反，条纹5和6似乎是通过不同机制激活的。条纹6的激活关键依赖于克尼普斯（kni），而条纹5可能需要激活蛋白（间隙和非间隙）的组合。为了开始从机制上理解条纹形成，我们在两个条纹增强子中定位了Kr蛋白的结合位点。条纹6增强子比条纹5增强子含有更高亲和力的Kr结合位点，这可能使两条条纹在不同的Kr蛋白浓度阈值下被抑制。我们还证明kni激活剂与条纹6增强子结合，并提供了Kr对条纹6抑制的竞争机制的证据。
