Joore J, Fasciana C, Speksnijder J E, Kruijer W, Destrée O H, van den Eijnden-van Raaij A J, de Laat S W, Zivkovic D
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht, The Netherlands.
Mech Dev. 1996 Mar;55(1):3-18. doi: 10.1016/0925-4773(95)00481-5.
Goosecoid is a homeobox gene that is expressed as an immediate early response to mesoderm induction by activin. We have investigated the induction of the zebrafish goosecoid promoter by the mesoderm inducing factors activin and basic fibroblast growth factor (bFGF) in dissociated zebrafish blastula cells, as well as by different wnts in intact embryos. Activin induces promoter activity, while bFGF shows a cooperative effect with activin. We have identified two enhancer elements that are functional in the induction of the goosecoid promoter. A distal element confers activin responsiveness to a heterologous promoter in the absence of de novo protein synthesis, whereas a proximal element responds only to a combination of activin and bFGF. Deletion experiments show that both elements are important for full induction by activin. Nuclear proteins that bind to these elements are expressed in blastula embryos, and competition experiments show that an octamer site in the activin responsive distal element is specifically bound, suggesting a role for an octamer binding factor in the regulation of goosecoid expression by activin. Experiments in intact embryos reveal that the proximal element contains sequences that respond to Xwnt1, but not to Xwnt5c. Furthermore, we show that the distal element is active in a confined dorsal domain in embryos and responds to overexpression of activin in vivo, as well as to dorsalization by lithium. The distal element is to our knowledge the first enhancer element identified that mediates the induction of a mesodermal gene by activin.
鹅膏蕈氨酸是一种同源异型盒基因，作为对激活素诱导中胚层的即时早期反应而表达。我们研究了中胚层诱导因子激活素和碱性成纤维细胞生长因子（bFGF）在解离的斑马鱼囊胚细胞中对斑马鱼鹅膏蕈氨酸启动子的诱导作用，以及完整胚胎中不同Wnt蛋白的诱导作用。激活素可诱导启动子活性，而bFGF与激活素表现出协同效应。我们鉴定出两个在鹅膏蕈氨酸启动子诱导中起作用的增强子元件。一个远端元件在无新蛋白质合成的情况下赋予异源启动子激活素反应性，而一个近端元件仅对激活素和bFGF的组合有反应。缺失实验表明，这两个元件对于激活素的完全诱导都很重要。与这些元件结合的核蛋白在囊胚胚胎中表达，竞争实验表明激活素反应性远端元件中的一个八聚体位点被特异性结合，这表明一个八聚体结合因子在激活素调节鹅膏蕈氨酸表达中起作用。在完整胚胎中的实验表明，近端元件包含对Xwnt1有反应但对Xwnt5c无反应的序列。此外，我们表明远端元件在胚胎的特定背侧区域有活性，并且在体内对激活素的过表达以及锂诱导的背化有反应。据我们所知，远端元件是第一个被鉴定出的介导激活素诱导中胚层基因的增强子元件。
