Study of the novel Nodal target genes : molecular mechanism of inhibition of the FGF signaling and involvement of mesoderm formation during Xenopus development.

XSPR2b基因是由非洲爪蟾Nodal信号的主要转录调控因子FAST-1诱导的基因。动物cap实验表明，XSPR2b基因的表达不仅受Nodal/FAST-1信号通路的诱导，还受FGF信号通路的诱导。该基因编码转录因子，在爪蟾发育早期主要在中胚层表达。该基因的表达域与中胚层形成的主要基因Xbra基因的表达域重叠。XSPR2b基因的过表达诱导了Xbra基因在胚胎中的异位表达，提示这些基因之间存在功能上的相互作用。在动物帽细胞中，过表达Xbra基因本身可以诱导一些中胚层基因，而XSPR2b基因则不能。当这两个基因在帽细胞中共表达时，xbra靶基因的诱导上调。然而，非xbra靶基因的表达没有被诱导。这些结果表明XSPR2b基因通过Xbra基因参与了爪蟾中胚层的形成。通过报告基因实验，发现野生型XSPR2b基因编码转录激活子。XSPR2b基因诱导Xbra基因的分子机制目前还在研究中。

The XSPR2b gene was isolated as the genes induced by FAST-1, a major transcriptional regulator of the Nodal signaling, from Xenopus laevis. It was shown that the expression of the XSPR2b gene was induced not only by the Nodal/FAST-1 signaling, but also the FGF signaling by using animal cap assay. This gene encodes transcription factor and is expressed mainly in the mesodermal region during the early Xenopus development. The expression domain is overlapped with those of Xbra gene, a major gene of mesoderm formation. Overexpression of the XSPR2b gene induced the ectopic expression of the Xbra gene in the embryos, suggesting the functional interaction between these genes. In the animal cap cells, overexpression of the Xbra gene itself could induce some mesodermal genes, whereas XSPR2b gene could not. When both genes were co-expressed in the cap cells, induction of the Xbra-target genes were up regulated. However, the expression of the none-Xbra target genes was not induced. These results suggested that XSPR2b gene has a role in mesoderm formation of Xenopus, through Xbra gene. By the reporter gene assay, wild type XSPR2b gene was shown to encode transcriptional activator. The molecular mechanism of the XSPR2b gene to induce the Xbra gene is currently under investigation.