Department of Biological Chemistry, Howard Hughes Medical Institute, University of California Los Angeles, Los Angeles, California, United States of America.
PLoS One. 2009 Aug 6;4(8):e6543. doi: 10.1371/journal.pone.0006543.
A key question in developmental biology is how growth factor signals are integrated to generate pattern. In this study we investigated the integration of the Drosophila BMP and Wingless/GSK3 signaling pathways via phosphorylations of the transcription factor Mad. Wingless was found to regulate the phosphorylation of Mad by GSK3 in vivo. In epistatic experiments, the effects of Wingless on wing disc molecular markers (senseless, distalless and vestigial) were suppressed by depletion of Mad with RNAi. Wingless overexpression phenotypes, such as formation of ectopic wing margins, were induced by Mad GSK3 phosphorylation-resistant mutant protein. Unexpectedly, we found that Mad phosphorylation by GSK3 and MAPK occurred in segmental patterns. Mad depletion or overexpression produced Wingless-like embryonic segmentation phenotypes. In Xenopus embryos, segmental border formation was disrupted by Smad8 depletion. The results show that Mad is required for Wingless signaling and for the integration of gradients of positional information.
发育生物学中的一个关键问题是，生长因子信号如何整合以产生模式。在这项研究中，我们通过转录因子 Mad 的磷酸化研究了果蝇 BMP 和 Wingless/GSK3 信号通路的整合。发现 Wingless 通过 GSK3 在体内调节 Mad 的磷酸化。在上位实验中，Mad 的 RNAi 耗尽抑制了 Wingless 对翼盘分子标记物（senseless、distalless 和 vestigial）的影响。Mad GSK3 磷酸化抗性突变蛋白的过表达表型，如异位翅缘的形成，被诱导。出乎意料的是，我们发现 Mad 由 GSK3 和 MAPK 磷酸化发生在节段模式中。Mad 的耗尽或过表达产生了 Wingless 样的胚胎分节表型。在非洲爪蟾胚胎中，Smad8 的耗尽破坏了节段边界的形成。结果表明，Mad 是 Wingless 信号传导和位置信息梯度整合所必需的。
