Papalopulu N
Salk Institute, La Jolla, California 92037, USA.
Perspect Dev Neurobiol. 1995;3(1):39-52.
The vertebrate central nervous system is subdivided into distinct regions along the anteroposterior axis. It has been suggested that segmentation may play an important role in the regionalization and patterning of the neural tube, in particular in the development of the hindbrain. Recent evidence suggests that this may be true also in the forebrain. Several criteria that have been used to define segments and that have led to different views on how the anterior neural tube is subdivided will be discussed. However, regionalization of the neural ectoderm is a gradual and continuous process that starts as early as the induction of neural ectoderm. At the neural plate stage, distinct domains of gene expression have been established, indicating that a certain amount of regionalization has already taken place. Segmentation, as defined by lineage restriction between proposed segments or by the formation of morphological segment boundaries, is not thought to have occurred at the neural plate. When viewed in this context, segmentation may be considered a relatively late event in the ontogenesis of the nervous system. The early pattern of gene expression, the organization of the neural plate, and the underlying signals and tissue interactions may provide us with a better understanding of how the forebrain is regionalized.
脊椎动物的中枢神经系统沿前后轴被细分为不同区域。有人提出，分段可能在神经管的区域化和模式形成中发挥重要作用，特别是在后脑的发育过程中。最近的证据表明，这在前脑可能也是如此。本文将讨论用于定义分段的几个标准，这些标准导致了关于前神经管如何细分的不同观点。然而，神经外胚层的区域化是一个逐渐且连续的过程，早在神经外胚层诱导时就开始了。在神经板阶段，已经建立了不同的基因表达区域，这表明一定程度的区域化已经发生。按照所提出的分段之间的谱系限制或形态学分段边界的形成来定义的分段，在神经板阶段被认为尚未发生。从这个角度来看，分段可能被视为神经系统个体发生中相对较晚的事件。早期的基因表达模式、神经板的组织以及潜在的信号和组织相互作用，可能会让我们更好地理解前脑是如何区域化的。
