Smith J L, Schoenwolf G C
Department of Anatomy, University of Utah, School of Medicine, Salt Lake City 84132.
J Exp Zool. 1989 Apr;250(1):49-62. doi: 10.1002/jez.1402500107.
Cells in the median hinge point (MHP) of the bending chick neural plate are tightly apposed to the underlying notochord. These cells differ from those in adjacent lateral neuroepithelial areas (L) in that MHP cells are short and mainly wedge-shaped and line a furrow, whereas L cells are tall and mainly spindle-shaped and do not line a furrow. Cell generation time also differs in these regions. These consistent differences are detectable only after the notochord has formed and established contact with the neural plate; it is unclear whether they result from self-differentiation or induction. Two experiments were performed to evaluate the hypothesis that MHP characteristics develop owing to inductive interactions between the notochord and overlying neuroepithelial cells. First, notochordless chick embryos were generated to determine whether midline neuroepithelial cells still developed typical MHP characteristics. In the absence of the notochord, such characteristics did not develop. Second, isolated segments of quail notochord were transplanted subjacent to L of chick hosts to ascertain whether the notochord is capable of inducing MHP characteristics in L cells. When transplanted notochordal segments established apposition with host L cells, the apposing L cells usually developed typical MHP characteristics. Collectively, these results provide strong evidence that the notochord plays an inductive role in the formation of MHP characteristics. This investigation further revealed that bending can occur in the absence of MHP characteristics, forming a neural tube with an abnormal morphology. Thus, the formation of such characteristics, particularly cell wedging, is not required for bending but plays a major role in generating the normal cross-sectional morphology of the neural tube.
正在弯曲的鸡胚神经板中间铰链点（MHP）处的细胞与下方的脊索紧密相邻。这些细胞与相邻的外侧神经上皮区域（L）中的细胞不同，MHP细胞短且主要呈楔形，排列在一条沟中，而L细胞高且主要呈纺锤形，不排列在沟中。这些区域的细胞生成时间也不同。只有在脊索形成并与神经板建立接触后，这些一致的差异才能被检测到；目前尚不清楚它们是由自我分化还是诱导产生的。进行了两项实验来评估MHP特征是由于脊索与上方神经上皮细胞之间的诱导相互作用而形成的这一假设。首先，生成无脊索的鸡胚，以确定中线神经上皮细胞是否仍会发育出典型的MHP特征。在没有脊索的情况下，这种特征不会发育。其次，将鹌鹑脊索的分离片段移植到鸡宿主的L区域下方，以确定脊索是否能够在L细胞中诱导出MHP特征。当移植的脊索片段与宿主L细胞相邻时，相邻的L细胞通常会发育出典型的MHP特征。总的来说，这些结果提供了强有力的证据，表明脊索在MHP特征的形成中起诱导作用。这项研究进一步揭示，在没有MHP特征的情况下也会发生弯曲，形成形态异常的神经管。因此，这种特征的形成，特别是细胞楔形化，对于弯曲不是必需的，但在生成神经管的正常横截面形态中起主要作用。
