Odenthal J, van Eeden F J, Haffter P, Ingham P W, Nüsslein-Volhard C
MPI für Entwicklungsbiologie, Spemannstrasse 35/III, Tübingen, 72076, Germany.
Dev Biol. 2000 Mar 15;219(2):350-63. doi: 10.1006/dbio.1999.9589.
The floor plate is a morphologically distinct structure of epithelial cells situated along the midline of the ventral spinal cord in vertebrates. It is a source of guidance molecules directing the growth of axons along and across the midline of the neural tube. In the zebrafish, the floor plate is about three cells wide and composed of cuboidal cells. Two cell populations can be distinguished by the expression patterns of several marker genes, including sonic hedgehog (shh) and the fork head-domain gene fkd4: a single row of medial floor plate (MFP) cells, expressing both shh and fkd4, is flanked by rows of lateral floor plate (LFP) cells that express fkd4 but not shh. Systematic mutant searches in zebrafish embryos have identified a number of genes, mutations in which visibly reduce the floor plate. In these mutants either the MFP or the LFP cells are absent, as revealed by the analysis of the shh and fkd4 expression patterns. MFP cells are absent, but LFP cells are present, in mutants of cyclops, one-eyed pinhead, and schmalspur, whose development of midline structures is affected. LFP cells are absent, but MFP cells are present, in mutants of four genes, sonic you, you, you-too, and chameleon, collectively called the you-type genes. This group of mutants also shows defects in patterning of the paraxial mesoderm, causing U- instead of V-shaped somites. One of the you-type genes, sonic you, was recently shown to encode the zebrafish Shh protein, suggesting that the you-type genes encode components of the Shh signaling pathway. It has been shown previously that in the zebrafish shh is required for the induction of LFP cells, but not for the development of MFP cells. This conclusion is supported by the finding that injection of shh RNA causes an increase in the number of LFP, but not MFP cells. Embryos mutant for iguana, detour, and umleitung share the lack of LFP cells with you-type mutants while somite patterning is not severely affected. In mutants that fail to develop a notochord, MFP cells may be present, but are always surrounded by LFP cells. These data indicate that shh, expressed in the notochord and/or the MFP cells, induces the formation of LFP cells. In embryos doubly mutant for cyclops (cyc) and sonic you (syu) both LFP and MFP cells are deleted. The number of primary motor neurons is strongly reduced in cyc;syu double mutants, while almost normal in single mutants, suggesting that the two different pathways have overlapping functions in the induction of primary motor neurons.
底板是脊椎动物腹侧脊髓中线处上皮细胞的一种形态上独特的结构。它是引导分子的来源，这些分子引导轴突沿着神经管中线生长并穿过中线。在斑马鱼中，底板约有三个细胞宽，由立方体细胞组成。根据几种标记基因的表达模式可以区分出两个细胞群体，包括音猬因子（shh）和叉头结构域基因fkd4：一排表达shh和fkd4的内侧底板（MFP）细胞，两侧是表达fkd4但不表达shh的外侧底板（LFP）细胞行。对斑马鱼胚胎进行的系统性突变体搜索已经鉴定出许多基因，这些基因的突变会明显减少底板。在这些突变体中，通过对shh和fkd4表达模式的分析发现，要么MFP细胞缺失，要么LFP细胞缺失。在独眼畸形、单眼针头畸形和短吻畸形的突变体中，MFP细胞缺失，但LFP细胞存在，这些突变体中线结构的发育受到影响。在四个基因（音猬你、你、你也和变色龙，统称为你型基因）的突变体中，LFP细胞缺失，但MFP细胞存在。这组突变体在近轴中胚层的模式形成上也表现出缺陷，导致体节呈U形而非V形。你型基因之一，音猬你，最近被证明编码斑马鱼的Shh蛋白，这表明你型基因编码Shh信号通路的组成部分。先前已经表明，在斑马鱼中，shh是诱导LFP细胞所必需的，但不是MFP细胞发育所必需的。这一结论得到以下发现的支持：注射shh RNA会导致LFP细胞数量增加，但不会导致MFP细胞数量增加。鬣蜥、绕道和改道突变体胚胎与你型突变体一样缺乏LFP细胞，而体节模式形成没有受到严重影响。在未能发育出脊索的突变体中，可能存在MFP细胞，但总是被LFP细胞包围。这些数据表明，在脊索和/或MFP细胞中表达的shh诱导了LFP细胞的形成。在独眼畸形（cyc）和音猬你（syu）双突变体胚胎中，LFP和MFP细胞都缺失。在cyc;syu双突变体中，初级运动神经元的数量大幅减少，而在单突变体中几乎正常，这表明这两种不同的途径在诱导初级运动神经元方面具有重叠功能。
