Flores-Saaib R D, Jia S, Courey A J
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA.
Development. 2001 May;128(10):1869-79. doi: 10.1242/dev.128.10.1869.
In the Drosophila embryo, Dorsal, a maternally expressed Rel family transcription factor, regulates dorsoventral pattern formation by activating and repressing zygotically active fate-determining genes. Dorsal is distributed in a ventral-to-dorsal nuclear concentration gradient in the embryo, the formation of which depends upon the spatially regulated inhibition of Dorsal nuclear uptake by Cactus. Using maternally expressed Gal4/Dorsal fusion proteins, we have explored the mechanism of activation and repression by Dorsal. We find that a fusion protein containing the Gal4 DNA-binding domain fused to full-length Dorsal is distributed in a nuclear concentration gradient that is similar to that of endogenous Dorsal, despite the presence of a constitutively active nuclear localization signal in the Gal4 domain. Whether this fusion protein activates or represses reporter genes depends upon the context of the Gal4-binding sites in the reporter. A Gal4/Dorsal fusion protein lacking the conserved Rel homology domain of Dorsal, but containing the non-conserved C-terminal domain also mediates both activation and repression, depending upon Gal4-binding site context. A region close to the C-terminal end of the C-terminal domain has homology to a repression motif in Engrailed - the eh1 motif. Deletion analysis indicates that this region mediates transcriptional repression and binding to Groucho, a co-repressor known to be required for Dorsal-mediated repression. As has previously been shown for repression by Dorsal, we find that activation by Dorsal, in particular by the C-terminal domain, is modulated by the maternal terminal pattern-forming system.
在果蝇胚胎中，背腹形态发生素（Dorsal）是一种由母体表达的Rel家族转录因子，它通过激活和抑制合子激活的命运决定基因来调节背腹模式形成。Dorsal在胚胎中以从腹侧到背侧的核浓度梯度分布，其形成依赖于仙人掌蛋白（Cactus）对Dorsal核摄取的空间调控抑制作用。利用母体表达的Gal4/Dorsal融合蛋白，我们探究了Dorsal激活和抑制的机制。我们发现，一种包含与全长Dorsal融合的Gal4 DNA结合结构域的融合蛋白，尽管在Gal4结构域中存在组成型活性核定位信号，但它仍以与内源性Dorsal相似的核浓度梯度分布。这种融合蛋白是激活还是抑制报告基因取决于报告基因中Gal4结合位点的背景。一种缺乏Dorsal保守Rel同源结构域但包含非保守C末端结构域的Gal4/Dorsal融合蛋白，同样也能介导激活和抑制作用，这取决于Gal4结合位点的背景。C末端结构域靠近C末端的一个区域与Engrailed中的一个抑制基序——eh1基序具有同源性。缺失分析表明，该区域介导转录抑制并与Groucho结合，Groucho是一种已知的Dorsal介导的抑制作用所需的共抑制因子。正如之前所显示的Dorsal的抑制作用一样，我们发现Dorsal的激活作用，特别是由C末端结构域介导的激活作用，受到母体末端模式形成系统的调节。
