Marchant L, Linker C, Ruiz P, Guerrero N, Mayor R
Laboratory of Developmental Biology, Faculty of Science, University of Chile, Santiago, Chile.
Dev Biol. 1998 Jun 15;198(2):319-29.
We have analyzed the role of mesoderm in the induction of the neural crest in Xenopus using expression of neural plate (Xsox-2) and neural crest (Xslug and ADAM). Conjugation experiments using different kinds of mesoderm together with embryonic dissection experiments suggest that the dorsolateral mesoderm is capable of specifically inducing neural crest cells. Neural crest markers can be induced in competent ectoderm at varying distances from the inducing mesoderm, with dorsal tissue inducing neural crest at a distance while dorsolateral tissue only induces neural crest directly in adjacent ectoderm. The results suggest that dorsal mesoderm has a high level of inducer and dorsolateral mesoderm has a lower level, consistent with a inductive gradient. We explored the possible role of BMP and noggin in the generation of such a hypothetical gradient and found that: (1) progressively higher levels of BMP activity are sufficient for the specification of neural plate, neural crest, and nonneural cells, respectively; (2) progressively higher levels of noggin are able to induce neural crest at greater distances from the source of inducer; and (3) modification of the levels of BMP activity causes induction of the neural crest in absence of neural plate, suggesting independent induction of these two tissues. We propose a model in which a gradient of BMP activity is established in the ectoderm by interaction between BMP in the ectoderm and BMP inhibitors in the mesoderm. Neural crest is induced when a threshold level of BMP is attained in the ectoderm. The dorsolateral mesoderm produces either BMP inhibitors or a specific neural crest inducer, with low BMP activity inducing neural plate while high BMP activity induces epidermis.
我们利用神经板（Xsox - 2）和神经嵴（Xslug和ADAM）的表达，分析了中胚层在非洲爪蟾神经嵴诱导过程中的作用。使用不同类型中胚层的结合实验以及胚胎解剖实验表明，背外侧中胚层能够特异性地诱导神经嵴细胞。神经嵴标记物可在与诱导中胚层不同距离的感受态外胚层中被诱导，背侧组织能在一定距离外诱导神经嵴，而背外侧组织仅直接在相邻外胚层中诱导神经嵴。结果表明，背侧中胚层具有高水平的诱导物，背外侧中胚层具有较低水平的诱导物，这与诱导梯度一致。我们探究了BMP和头蛋白在产生这种假设梯度中的可能作用，发现：（1）逐渐升高的BMP活性水平分别足以指定神经板、神经嵴和非神经细胞；（2）逐渐升高的头蛋白水平能够在距诱导源更远的距离诱导神经嵴；（3）BMP活性水平的改变导致在没有神经板的情况下诱导神经嵴，表明这两种组织的独立诱导。我们提出一个模型，其中通过外胚层中的BMP与中胚层中的BMP抑制剂之间的相互作用，在外胚层中建立了BMP活性梯度。当外胚层中达到BMP的阈值水平时，就会诱导神经嵴。背外侧中胚层产生BMP抑制剂或一种特定的神经嵴诱导物，低BMP活性诱导神经板，而高BMP活性诱导表皮。
