La Rosée A, Häder T, Taubert H, Rivera-Pomar R, Jäckle H
Abteilung Molekulare Entwicklungsbiologie, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
EMBO J. 1997 Jul 16;16(14):4403-11. doi: 10.1093/emboj/16.14.4403.
Pair-rule gene hairy (h) expression in seven evenly spaced stripes, along the longitudinal axis of the Drosophila blastoderm embryo, is mediated by a modular array of separate stripe enhancer elements. The minimal enhancer element, which generates reporter gene expression in place of the most posterior h stripe 7 (h7-element), contains a dense array of binding sites for factors providing the trans-acting control of h stripe 7 expression as revealed by genetic analyses. The h7-element mediates position-dependent gene expression by sensing region-specific combinations and concentrations of both the maternal homeodomain transcriptional activators, Caudal and Bicoid, and of transcriptional repressors encoded by locally expressed zygotic gap genes. Caudal and Bicoid, which form complementing concentration gradients along the longitudinal axis of the embryo, function as redundant activators, indicating that the anterior determinant Bicoid is able to activate gene expression in the most posterior region of the embryo. The spatial limits of the h stripe-7 domain are brought about by the local activities of repressors which prevent activation. The results suggest that the gradients of Bicoid and Caudal combine their activities to activate segmentation genes along the entire axis of the embryo.
成对规则基因hairy（h）在果蝇囊胚胚胎纵轴上以七条等距条纹的形式表达，这是由一系列独立的条纹增强子元件介导的。最小的增强子元件，它能替代最靠后的h条纹7（h7元件）产生报告基因表达，包含一系列密集的因子结合位点，这些因子通过遗传分析揭示了对h条纹7表达的反式作用控制。h7元件通过感知母体同源域转录激活因子Caudal和Bicoid以及由局部表达的合子间隙基因编码的转录抑制因子的区域特异性组合和浓度，介导位置依赖性基因表达。Caudal和Bicoid沿着胚胎纵轴形成互补的浓度梯度，作为冗余激活因子起作用，这表明前部决定因子Bicoid能够在胚胎最靠后的区域激活基因表达。h条纹7区域的空间界限是由阻止激活的抑制因子的局部活性造成的。结果表明，Bicoid和Caudal的梯度结合它们的活性，沿着胚胎的整个轴激活分割基因。
