Zhang Chi, Basta Tamara, Fawcett Shana R, Klymkowsky M W
Molecular, Cellular and Developmental Biology, University of Colorado, Porter Biosci. Building, Boulder, CO 80309-0347, USA.
Dev Biol. 2005 Feb 15;278(2):526-41. doi: 10.1016/j.ydbio.2004.11.008.
In zebrafish, the divergent F-type SOX casanova acts downstream of Nodal signaling to specify endoderm. While no casanova orthologs have been identified in tetrapods, the F-type SOX, SOX7, is supplied maternally in Xenopus (Fawcett and Klymkowsky, 2004. GER 4, 29). Subsequent RT-PCR and section-based in situ hybridization analyses indicate that SOX7 mRNA is localized to the vegetal region of the blastula-stage embryo. Overexpression and maternal depletion studies reveal that the T-box transcription factor VegT, which initiates mesoendodermal differentiation, directly regulates SOX7 expression. SOX7, but not SOX17 (another F-type SOX), binds to sites within the Xnr5 promoter and SOX7, but not SOX17, induces expression of the Nodal-related genes Xnr1, Xnr2, Xnr4, Xnr5, and Xnr6, the homeodomain transcription factor Mixer, and the endodermal marker SOX17beta; both SOX7 and SOX17 induce expression of the pan-endodermal marker endodermin. SOX7's induction of Xnr expression in animal caps is independent of Mixer and Nodal signaling. In animal caps, VegT's ability to induce Mixer and Edd appears to depend upon SOX7 activity. Whole embryo experiments suggests that vegetal factors partially compensate for the absence of SOX7. Based on the antagonistic effects of SOX7 and SOX3 (Zhang et al., 2004. Dev. Biol. 273, 23) and their common binding sites in the Xnr5 promoter, we propose a model in which competitive interactions between these two proteins are involved in refining the domain of endodermal differentiation.
在斑马鱼中，不同的F型SOX蛋白“卡萨诺瓦”在Nodal信号下游发挥作用，决定内胚层的形成。虽然在四足动物中尚未鉴定出“卡萨诺瓦”的直系同源物，但F型SOX蛋白SOX7在非洲爪蟾中是母源提供的（福西特和克利姆科夫斯基，2004年。《发育、进化与遗传学》4，29）。随后的逆转录聚合酶链反应（RT-PCR）和基于切片的原位杂交分析表明，SOX7信使核糖核酸（mRNA）定位于囊胚期胚胎的植物区域。过表达和母源缺失研究表明，启动中内胚层分化的T盒转录因子VegT直接调节SOX7的表达。SOX7而非SOX17（另一种F型SOX蛋白）与Xnr5启动子内的位点结合，并且SOX7而非SOX17诱导Nodal相关基因Xnr1、Xnr2、Xnr4、Xnr5和Xnr6、同源结构域转录因子Mixer以及内胚层标记物SOX17β的表达；SOX7和SOX17都诱导泛内胚层标记物内胚层素的表达。SOX7在动物帽中诱导Xnr表达独立于Mixer和Nodal信号。在动物帽中，VegT诱导Mixer和Edd的能力似乎取决于SOX7的活性。全胚胎实验表明，植物因子部分补偿了SOX7的缺失。基于SOX7和SOX3的拮抗作用（张等人，2004年。《发育生物学》273，23）以及它们在Xnr5启动子中的共同结合位点，我们提出了一个模型，其中这两种蛋白质之间的竞争性相互作用参与了细化内胚层分化区域的过程。
