Pera E M, Kessel M
Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
Development. 1997 Oct;124(20):4153-62. doi: 10.1242/dev.124.20.4153.
We analysed the role of the prechordal plate in forebrain development of chick embryos in vivo. After transplantation to uncommitted ectoderm a prechordal plate induces an ectopic, dorsoventrally patterned, forebrain-like vesicle. Grafting laterally under the anterior neural plate causes ventralization of the lateral side of the forebrain, as indicated by a second expression domain of the homeobox gene NKX2.1. Such a lateral ventralization cannot be induced by the secreted factor Sonic Hedgehog alone, as this is only able to distort the ventral forebrain medially. Removal of the prechordal plate does not reduce the rostrocaudal extent of the anterior neural tube, but leads to significant narrowing and cyclopia. Excision of the head process results in the caudal expansion of the NKX2.1 expression in the ventral part of the anterior neural tube, while PAX6 expression in the dorsal part remains unchanged. We suggest that there are three essential steps in early forebrain patterning, which culminate in the ventralization of the forebrain. First, anterior neuralization occurs at the primitive streak stage, when BMP-4-antagonizing factors emanate from the node and spread in a planar fashion to induce anterior neural ectoderm. Second, the anterior translocation of organizer-derived cells shifts the source of neuralizing factors anteriorly, where the relative concentration of BMP-4-antagonists is thus elevated, and the medial part of the prospective forebrain becomes competent to respond to ventralizing factors. Third, the forebrain anlage is ventralized by signals including Sonic Hedgehog, thereby creating a new identity, the prospective hypothalamus, which splits the eye anlage into two lateral domains.
我们在体内分析了原条前板在鸡胚前脑发育中的作用。将原条前板移植到未分化的外胚层后，它可诱导形成一个异位的、具有背腹模式的前脑样囊泡。向前神经板下方侧面移植会导致前脑侧面腹侧化，同源框基因NKX2.1的第二个表达域可表明这一点。单独的分泌因子音猬因子无法诱导这种侧面腹侧化，因为它只能使前脑腹侧部分向内侧变形。去除原条前板不会减小前神经管的前后长度，但会导致其显著变窄并出现独眼畸形。切除头部突起会导致NKX2.1在前神经管腹侧部分的表达向尾侧扩展，而背侧部分的PAX6表达保持不变。我们认为，早期前脑模式形成有三个关键步骤，最终导致前脑腹侧化。首先，在原条阶段发生前神经化，此时来自节点的骨形态发生蛋白4（BMP-4）拮抗因子以平面方式扩散，诱导前神经外胚层形成。其次，组织者来源细胞的向前移位将神经化因子的来源向前移动，从而提高了BMP-4拮抗剂的相对浓度，使预期前脑的内侧部分有能力对腹侧化因子作出反应。第三，前脑原基通过包括音猬因子在内的信号腹侧化，从而产生一个新的身份，即预期的下丘脑，它将眼原基分成两个外侧区域。
