Takahashi K, Okamura Y
Department of Neurobiology, Faculty of Medicine, University of Tokyo, Japan.
Perspect Dev Neurobiol. 1995;2(4):317-25.
Neural induction in vertebrate embryos has been mainly studied in multicellular systems composed of pieces excised from ectoderm and mesoderm of amphibian embryos. A simple model system for neural induction has been established from the cleavage-arrested 8-cell ascidian embryo by pairing a single ectodermal with a single vegetal blastomere, as a competent and a inducer cell, respectively. This induction, mediated by specific cell contact, can be mimicked by treating with serine protease. In this simple model system, the turnover of subtypes of Na+ channels occurs, dependent on new transcriptional activities after neural induction. A cloned ascidian Na+ channel gene, TuNa I, is especially useful for analysis of the neural induction on the gene regulation level, and can serve as a specific marker for neuronal differentiation in the ascidian tadpole larva. In contrast to Na+ channels, transcription of inward rectifier K+ channels is suppressed immediately after neural induction. Since the inward rectifier is one of several genes expressed early in epidermal cells, we conclude that the inductive signal not only enhances the transcription of neural characters, but also suppresses that of non-neural characters.
脊椎动物胚胎中的神经诱导主要是在由从两栖动物胚胎的外胚层和中胚层切下的组织组成的多细胞系统中进行研究的。通过将单个外胚层细胞与单个植物性卵裂球配对，分别作为感受态细胞和诱导细胞，从卵裂阻滞的8细胞海鞘胚胎建立了一个简单的神经诱导模型系统。这种由特定细胞接触介导的诱导可以通过丝氨酸蛋白酶处理来模拟。在这个简单的模型系统中，Na⁺通道亚型的转换发生，这依赖于神经诱导后的新转录活性。一个克隆的海鞘Na⁺通道基因TuNa I，对于在基因调控水平分析神经诱导特别有用，并且可以作为海鞘蝌蚪幼虫神经元分化的特异性标记。与Na⁺通道相反，内向整流K⁺通道的转录在神经诱导后立即受到抑制。由于内向整流通道是在表皮细胞中早期表达的几个基因之一，我们得出结论，诱导信号不仅增强神经特征的转录，而且抑制非神经特征的转录。
