Lawson A, England M A
Department of Pre-Clinical Sciences, Faculty of Medicine, University of Leicester, England.
Dev Dyn. 1998 Aug;212(4):473-81. doi: 10.1002/(SICI)1097-0177(199808)212:4<473::AID-AJA1>3.0.CO;2-E.
Cranial neural fold fusion in the chick embryo is known to commence in the midbrain region before progressing cranially and caudally to involve the fore- and hindbrain regions, respectively. The two epithelial layers at the tips of the neural folds that participate in fusion are the surface ectoderm and the neuroepithelium. We have examined and compared cranial neural fold fusion in both layers, and our results show that fusion of the neuroepithelial component of the neural folds, unlike that of the surface ectoderm, starts in the caudal portion of the forebrain. Second, contrary to the widely accepted opinion, we have demonstrated that in the hindbrain region, fusion of the neuroepithelial component of the neural folds does not occur. Soon after neural fold apposition, a neuroepithelial eminence appears in rhombomeres 1 and 2, and this, together with other neuroepithelial cells in the dorsal midline of the hindbrain, undergoes massive apoptosis. The absence of neuroepithelial fusion in the hindbrain may be due to the presence of massive apoptosis among neuroepithelial cells that should have participated in the fusion process. The events described above may predispose the hindbrain to the development of neural tube defects. The appearance of cranial neural crest cells in the midline during their migration may enhance the fusion of the surface ectodermal portion of the neural folds.
已知鸡胚中的颅神经褶融合在中脑区域开始，然后分别向头端和尾端推进，涉及前脑和后脑区域。参与融合的神经褶尖端的两个上皮层是表面外胚层和神经上皮。我们检查并比较了这两层中的颅神经褶融合情况，结果表明，与表面外胚层不同，神经褶的神经上皮成分的融合始于前脑的尾端部分。其次，与广泛接受的观点相反，我们证明在后脑区域，神经褶的神经上皮成分不会发生融合。神经褶并置后不久，菱脑节1和2中会出现神经上皮隆起，并且它与后脑背中线的其他神经上皮细胞一起经历大量凋亡。后脑神经上皮融合的缺失可能是由于本应参与融合过程的神经上皮细胞中存在大量凋亡。上述事件可能使后脑易患神经管缺陷。颅神经嵴细胞在迁移过程中出现在中线可能会增强神经褶表面外胚层部分的融合。
