Weber Joseph R, Sokol Sergei Y
Department of Microbiology and Molecular Genetics, Harvard Medical School and Molecular Medicine Unit, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215, USA.
Mech Dev. 2003 Aug;120(8):955-64. doi: 10.1016/s0925-4773(03)00082-0.
Multiple signaling pathways are involved in the induction of the organizer, a major center controlling vertebrate body plan formation. To study these signals, we have focused on the regulation of the Zic3 gene, which codes for a zinc finger transcription factor expressed in the organizer region at the beginning of gastrulation. We searched for DNA regulatory elements in the Zic3 promoter by testing their ability to drive reporter gene expression in early embryos. By this approach, we identified an activin responsive enhancer (Zic3-ARE), which was located in the Zic3 first intron and was essential for dorsal activation of the reporter. The Zic3-ARE was stimulated by activin and Nodal ligands, but not by a dominant negative bone morphogenetic protein (BMP) receptor. The Zic3-ARE contains a repeating consensus homeodomain binding sequence, CTAATTAAA, suggesting involvement of a homeodomain transcription factor(s). Mutations in this motif abolished enhancer activity in dorsal marginal zone and its response to activin in animal pole explants. Inhibition of either Wnt/beta-catenin or activin/Nodal signaling suppressed Zic3-ARE activity in dorsal blastomeres, further illustrating the importance of these pathways in activation of organizer genes.
多种信号通路参与了组织者的诱导过程，组织者是控制脊椎动物身体模式形成的主要中心。为了研究这些信号，我们聚焦于Zic3基因的调控，该基因编码一种锌指转录因子，在原肠胚形成初期在组织者区域表达。我们通过测试其在早期胚胎中驱动报告基因表达的能力，在Zic3启动子中寻找DNA调控元件。通过这种方法，我们鉴定出一个激活素反应增强子（Zic3-ARE），它位于Zic3的第一个内含子中，对报告基因的背侧激活至关重要。Zic3-ARE受到激活素和Nodal配体的刺激，但不受显性负性骨形态发生蛋白（BMP）受体的刺激。Zic3-ARE包含一个重复的共有同源结构域结合序列CTAATTAAA，提示有同源结构域转录因子参与。该基序中的突变消除了背侧边缘区的增强子活性及其在动物极外植体中对激活素的反应。抑制Wnt/β-连环蛋白或激活素/Nodal信号通路会抑制背侧卵裂球中的Zic3-ARE活性，进一步说明了这些信号通路在激活组织者基因中的重要性。
