Rastegar S, Friedle H, Frommer G, Knöchel W
Abteilung Biochemie, Universität Ulm, Albert Einstein Allee 11, 89081, Ulm, Germany.
Mech Dev. 1999 Mar;81(1-2):139-49. doi: 10.1016/s0925-4773(98)00239-1.
The Xvent homeobox multigene family is essential for the patterning of the ventral mesoderm in Xenopus embryos. We have identified two novel members of this family, Xvent-1B and Xvent-2B, and have characterized their genomic structures. These two genes show a clustered organization and have probably arisen by gene duplication with subsequent inversion. Cis-regulatory elements within the promoters of both genes have been identified which contribute to their spatial activation. Xvent-2B is activated by BMP-2/4 in the absence of de novo protein synthesis, suggesting that this gene is a direct target of BMP-signalling. In contrast, Xvent-1B does not directly respond to BMP-2/4, but is activated by Xvent-2B. This activation is documented by Xvent-1B promoter/reporter studies, Xvent-2B overexpression and loss-of-function analysis using a dominant-negative Xvent-2 mutant. However, cycloheximide experiments reveal that Xvent-2B by itself is not sufficient to activate transcription of the Xvent-1B gene, but that there is a requirement for additional factor(s) being synthesized after midblastula transition.
Xvent 同源框多基因家族对于非洲爪蟾胚胎腹侧中胚层的模式形成至关重要。我们鉴定出了该家族的两个新成员，即Xvent-1B和Xvent-2B，并对它们的基因组结构进行了表征。这两个基因呈现出成簇排列，可能是通过基因复制并随后发生倒位而产生的。已确定这两个基因启动子内的顺式调控元件，它们有助于基因的空间激活。在没有从头蛋白质合成的情况下，Xvent-2B被BMP-2/4激活，这表明该基因是BMP信号传导的直接靶点。相比之下，Xvent-1B不直接响应BMP-2/4，而是被Xvent-2B激活。通过Xvent-1B启动子/报告基因研究、Xvent-2B过表达以及使用显性负性Xvent-2突变体进行的功能丧失分析证实了这种激活。然而，放线菌酮实验表明，Xvent-2B自身不足以激活Xvent-1B基因的转录，而是需要在囊胚中期转变后合成额外的因子。
