UPMC Univ Paris 06-CNRS, UMR 7009 Biologie du Développement Observatoire Océanologique, 06230 Villefranche-sur-mer, France.
Development. 2010 Jan;137(2):223-35. doi: 10.1242/dev.042531.
Nodal factors play fundamental roles in induction and patterning of the mesoderm and endoderm in vertebrates, but whether this reflects an ancient role or one that evolved recently in vertebrates is not known. Here, we report that in addition to its primary role in patterning the ectoderm, sea urchin Nodal is crucial for patterning of the endoderm and skeletogenic mesoderm through the regulation of the expression of key transcription factors and signalling molecules, including BMP2/4 and FGFA. In addition, we uncovered an essential role for Nodal and BMP2/4 in the formation and patterning of the non-skeletogenic mesoderm. By comparing the effects of misexpressing Nodal or an activated Nodal receptor in clones of cells, we provide evidence that Nodal acts over a long range in the endomesoderm and that its effects on the blastocoelar cell precursors are likely to be direct. The activity of Nodal and BMP2/4 are antagonistic, and although bmp2/4 is transcribed in the ventral ectoderm downstream of Nodal, the BMP2/4 ligand is translocated to the dorsal side, where it activates signalling in the dorsal primary mesenchyme cells, the dorsal endoderm and in pigment cell precursors. Therefore, correct patterning of the endomesoderm depends on a balance between ventralising Nodal signals and dorsalising BMP2/4 signals. These experiments confirm that Nodal is a key regulator of dorsal-ventral polarity in the sea urchin and support the idea that the ventral ectoderm, like the Spemann organiser in vertebrates, is an organising centre that is required for patterning all three germ layers of the embryo.
节点因子在脊椎动物中中胚层和内胚层的诱导和模式形成中起着基本作用，但这是否反映了它们在脊椎动物中古老的作用还是最近进化而来的作用尚不清楚。在这里，我们报告说，除了在表皮模式形成中的主要作用外，海胆 Nodal 对于内胚层和骨架形成中胚层的模式形成也至关重要，这是通过调节关键转录因子和信号分子的表达来实现的，包括 BMP2/4 和 FGFA。此外，我们还揭示了 Nodal 和 BMP2/4 在非骨架形成中胚层的形成和模式形成中的重要作用。通过比较在细胞克隆中异位表达 Nodal 或激活的 Nodal 受体的效果，我们提供了证据表明 Nodal 在中肠内胚层中起长程作用，并且它对胚囊腔细胞前体的作用可能是直接的。Nodal 和 BMP2/4 的活性是拮抗的，尽管 bmp2/4 在 Nodal 下游的腹侧外胚层中转录，但 BMP2/4 配体被转运到背侧，在那里它激活背侧初级间充质细胞、背侧内胚层和色素细胞前体中的信号转导。因此，中肠内胚层的正确模式形成取决于腹侧 Nodal 信号和背侧 BMP2/4 信号之间的平衡。这些实验证实了 Nodal 是海胆背腹极性的关键调节因子，并支持这样的观点，即腹侧外胚层与脊椎动物的 Spemann 组织者一样，是一个组织中心，对于胚胎三个胚层的模式形成都是必需的。
