Schulz C, Tautz D
Zoologisches Institut, Universität München, Germany.
Development. 1994 Oct;120(10):3043-9. doi: 10.1242/dev.120.10.3043.
The subdivision of the anterior-posterior axis in Drosophila is achieved by a cascade of spatially regulated transcription factors which form short-range gradients at the syncytial blastoderm stage. These factors are assumed to have concentration-dependent regulatory effects on their target genes. However, there is so far little direct in vivo evidence that a single factor can autonomously activate and repress a given target gene. We have analysed here the regulatory capabilities of the gap gene hunchback by creating an artificial gradient of hunchback in the early embryo. This was achieved by providing the maternally expressed mRNA of hunchback with the anterior localization signal of the bicoid RNA. The effects of this artificial hunchback gradient were then studied in different types of mutant background. We show that under these conditions hb is autonomously capable of activating the target gene Krüppel at low concentrations and repressing it at high concentrations. In addition, we show that the artificially created hunchback gradient can organize a large part of the segment pattern, although it is expressed at a different position and in a different shape than the wild-type gradient of hunchback.
果蝇前后轴的划分是通过一系列空间调控的转录因子实现的，这些转录因子在合胞体胚盘阶段形成短程梯度。这些因子被认为对其靶基因具有浓度依赖性的调控作用。然而，到目前为止，几乎没有直接的体内证据表明单个因子能够自主激活和抑制给定的靶基因。我们在此通过在早期胚胎中创建驼背基因（hunchback）的人工梯度，分析了该间隙基因的调控能力。这是通过为母源表达的驼背基因mRNA提供双尾RNA的前侧定位信号来实现的。然后在不同类型的突变背景下研究这种人工驼背梯度的影响。我们表明，在这些条件下，驼背基因在低浓度时能够自主激活靶基因Krüppel，在高浓度时则抑制它。此外，我们表明，人工创建的驼背梯度能够组织大部分的体节模式，尽管它的表达位置和形状与野生型驼背梯度不同。
