Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, 1110 Biomedical Research Building 2/3, 421 Curie Boulevard, Philadelphia, PA 19104-6058, USA.
Dev Biol. 2010 Jun 1;342(1):39-50. doi: 10.1016/j.ydbio.2010.03.017. Epub 2010 Mar 25.
Establishment of the embryonic mesoderm is dependent on integration of multiple signaling and transcriptional inputs. We report that the transcriptional regulator Foxd3 is essential for dorsal mesoderm formation in zebrafish, and that this function is dependent on the Nodal pathway. Foxd3 gain-of-function results in expanded dorsal mesodermal gene expression, including the Nodal-related gene cyclops, and body axis dorsalization. Foxd3 knockdown embryos displayed reduced expression of cyclops and mesodermal genes, axial defects similar to Nodal pathway loss-of-function, and Nodal pathway activation rescued these phenotypes. In MZoep mutants inactive for Nodal signaling, Foxd3 did not rescue mesoderm formation or axial development, indicating that the mesodermal function of Foxd3 is dependent on an active downstream Nodal pathway. A previously identified foxd3 mutant, sym1, was described as a predicted null mutation with neural crest defects, but no mesodermal or axial phenotypes. We find that Sym1 protein retains activity and can induce strong mesodermal expansion and axial dorsalization. A subset of sym1 homozygotes displays axial defects and reduced cyclops and mesodermal gene expression, and penetrance of the mesodermal phenotypes is enhanced by Foxd3 knockdown. Therefore, sym1 is a hypomorphic allele, and reduced Foxd3 function results in a reduction of cyclops expression, and subsequent mesodermal and axial defects. These results demonstrate that Foxd3 is an essential upstream regulator of the Nodal pathway in zebrafish dorsal mesoderm development and establish a broadly conserved role for Foxd3 in vertebrate mesodermal development.
胚胎中胚层的建立依赖于多种信号和转录输入的整合。我们报告说，转录调节因子 Foxd3 对于斑马鱼背侧中胚层的形成是必需的，并且这个功能依赖于 Nodal 途径。Foxd3 的功能获得导致背侧中胚层基因表达的扩大，包括 Nodal 相关基因 cyclops 和体轴背侧化。Foxd3 敲低胚胎显示 cyclops 和中胚层基因的表达减少，与 Nodal 途径功能丧失相似的轴缺陷，并且 Nodal 途径的激活挽救了这些表型。在 MZoep 突变体中，Nodal 信号失活，Foxd3 不能挽救中胚层的形成或轴的发育，表明 Foxd3 的中胚层功能依赖于一个活跃的下游 Nodal 途径。先前鉴定的 foxd3 突变体 sym1 被描述为具有神经嵴缺陷的预测无效突变体，但没有中胚层或轴的表型。我们发现 Sym1 蛋白保留活性，并且可以诱导强烈的中胚层扩张和轴的背侧化。sym1 的一部分纯合子显示出轴缺陷和 cyclops 和中胚层基因表达减少，并且 Foxd3 敲低增强了中胚层表型的穿透性。因此，sym1 是一个弱等位基因，Foxd3 功能的降低导致 cyclops 表达的减少，随后是中胚层和轴的缺陷。这些结果表明，Foxd3 是斑马鱼背侧中胚层发育中 Nodal 途径的一个必需的上游调节因子，并确立了 Foxd3 在脊椎动物中胚层发育中的广泛保守作用。
