PDF(Pubmed)
Abstract：
The reciprocal inhibition between two signaling centers, the Spemann organizer (dorsal mesoderm) and ventral region (mesoderm and ectoderm), collectively regulate the overall development of vertebrate embryos. Each center expresses key homeobox transcription factors (TFs) that directly control target gene transcription. Goosecoid (Gsc) is an organizer (dorsal mesoderm)-specific TF known to induce dorsal fate and inhibit ventral/ectodermal specification. Ventx1.1 (downstream of Bmp signaling) induces the epidermal lineage and inhibits dorsal organizer-specific genes from the ventral region. Chordin (Chrd) is an organizer-specific secreted Bmp antagonist whose expression is primarily activated by Gsc. Alternatively, chrd expression is repressed by Bmp/Ventx1.1 in the ventral/epidermal region. However, the regulatory mechanisms underlying the transcription mediated by Gsc and Ventx1.1 remain elusive. Here, we found that the chrd promoter contained two cis-acting response elements that responded negatively to Ventx1.1 and positively to Gsc. In the ventral/ectodermal region, Ventx1.1 was directly bound to the Ventx1.1 response element (VRE) and inhibited chrd transcription. In the organizer region, Gsc was bound to the Gsc response elements (GRE) to activate chrd transcription. The Gsc-mediated positive response on the chrd promoter completely depended on another adjacent Wnt response cis-acting element (WRE), which was the TCF7 (also known as Tcf1) binding element. Site-directed mutagenesis of VRE, GRE, or WRE completely abolished the repressive or activator activity of Ventx1.1 and Gsc, respectively. The ChIP-PCR results confirmed the direct binding of Ventx1.1 and Gsc/Tcf7 to VRE and GRE/WRE, respectively. These results demonstrated that chrd expression is oppositely modulated by homeobox TFs, Ventx1.1, and Gsc/Tcf7 during the embryonic patterning of Xenopus gastrula.
摘要：
两个信号中心之间的相互抑制，Spemann组织者（背侧中胚层）和腹侧区域（中胚层和外胚层），共同调节脊椎动物胚胎的整体发育。每个中心表达直接控制靶基因转录的关键同源盒转录因子(TF)。Goosecoid（Gsc）是一种组织者（背侧中胚层）特异性TF，已知可诱导背侧命运并抑制腹侧/外胚层规格。Ventx1.1（Bmp信号的下游）诱导表皮谱系并抑制腹侧区域的背侧组织者特异性基因。Chordin（Chrd）是一种组织者特异性分泌的Bmp拮抗剂，其表达主要由Gsc激活。或者，在腹侧/表皮区域中，Bmp/Ventx1.1抑制了chrd表达。然而,Gsc和Ventx1.1介导的转录调控机制仍然难以捉摸。这里,我们发现，chrd启动子含有两个顺式作用反应元件，对Ventx1.1负反应，对Gsc正反应。在腹侧/外胚层区域，Ventx1.1直接与Ventx1.1反应元件(VRE)结合并抑制chrd转录。在组织者区域中，Gsc与Gsc反应元件(GRE)结合以激活chrd转录。Gsc介导的对chrd启动子的阳性反应完全依赖于另一个相邻的Wnt反应顺式作用元件(WRE),即TCF7(也称为Tcf1)结合元件。VRE的定点诱变,GRE,或WRE完全废除了Ventx1.1和GSC的抑制或激活活性，分别。ChIP-PCR结果证实了Ventx1.1和Gsc/Tcf7与VRE和GRE/WRE的直接结合，分别。这些结果表明，chrd表达被同源异型盒TFs相反地调节，非洲爪狼胚胎形成过程中的Ventx1.1和Gsc/Tcf7。
