Phillips C R
Bowdoin College, Brunswick, Maine 04011.
Methods Cell Biol. 1991;36:329-46.
The study of neural induction in Xenopus can be approached from two broad perspectives. One can study the competence of the ectoderm to respond to neural induction signals and any potential prepattern within the ectoderm. The second area of study involves the neural induction signals, in terms of the chemical nature of the signals, their sources, and their method of delivery. The neural competence of ectoderm has been studied by either grafting the ectoderm into areas which normally form neural tissue or by grafting tissues which normally induce neural structures onto the ectoderm to be tested. In general, it appears that ectoderm loses neural competence by midgastrula. However, there is some experimental evidence from various amphibian studies that the loss of neural competence in ectoderm does not occur simultaneously throughout all regions. It is not yet known if this phenomenon is also true in Xenopus. There appear to be several signaling events involved in the process of neural induction. Molecular probes have made it possible to study early steps in the neural induction and patterning processes which were not possible to study using only the development of neural morphology as a marker for neural induction. Antibodies directed against early epidermal versus neural epithelium indicate that the dorsal animal blastomeres are biased toward a neural pathway during early cleavage. Another signaling event occurs at early gastrula and the resulting dorsal ectoderm now responds more readily to some neural induction events than does the ventral ectoderm. The source of the early gastrula signals has been studied by a variety of methods, including exogastrula embryos, Keller sandwiches, and grafting a blastopore lip to the edge of competent ectoderm. The blastopore lip can send signals through the plane of the ectoderm capable of inducing competent ectoderm to become neural tissue. There are several issues relative to the process of neural induction which are not yet resolved. The major issue involves the mechanism of establishing pattern within the neural plate. Ectoderm appears to lose neural competence prior to the time when involuted dorsal mesoderm comes to underlie the anterior neural plate region. Several investigators have shown that information for expression of spatially restricted neural-specific molecules can travel through the ectoderm, independent of underlying dorsal mesoderm.(ABSTRACT TRUNCATED AT 400 WORDS)
非洲爪蟾神经诱导的研究可以从两个宽泛的角度进行。一方面可以研究外胚层对神经诱导信号作出反应的能力以及外胚层内任何潜在的预模式。研究的第二个方面涉及神经诱导信号，包括信号的化学性质、来源及其传递方式。外胚层的神经感受性已经通过将外胚层移植到正常形成神经组织的区域，或者通过将正常诱导神经结构的组织移植到待测试的外胚层上进行了研究。一般来说，外胚层在原肠胚中期似乎会丧失神经感受性。然而，来自各种两栖动物研究的一些实验证据表明，外胚层神经感受性的丧失并非在所有区域同时发生。目前尚不清楚这种现象在非洲爪蟾中是否也成立。神经诱导过程似乎涉及多个信号传导事件。分子探针使得研究神经诱导和模式形成过程中的早期步骤成为可能，而仅以神经形态发育作为神经诱导的标志物是无法进行这些研究的。针对早期表皮与神经上皮的抗体表明，背侧动物卵裂球在早期卵裂期间倾向于神经分化途径。另一个信号传导事件发生在原肠胚早期，此时产生的背侧外胚层现在比腹侧外胚层更容易对某些神经诱导事件作出反应。原肠胚早期信号的来源已经通过多种方法进行了研究，包括外胚层外翻胚胎、凯勒三明治以及将胚孔唇移植到感受性外胚层边缘。胚孔唇可以通过外胚层平面发送信号，能够诱导感受性外胚层变成神经组织。与神经诱导过程相关的几个问题尚未得到解决。主要问题涉及在神经板内建立模式的机制。在外卷的背侧中胚层位于前神经板区域下方之前，外胚层似乎就已经丧失了神经感受性。几位研究人员已经表明，空间受限的神经特异性分子表达的信息可以通过外胚层传递，而与下方的背侧中胚层无关。（摘要截断于400字）
