Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
Dev Biol. 2010 Aug 15;344(2):836-48. doi: 10.1016/j.ydbio.2010.05.514. Epub 2010 Jun 9.
Trigeminal sensory neurons develop from the neural crest and neurogenic placodes, and have been studied as a principal model of sensory neuron formation. While the Notch pathway has been extensively characterized in central nervous system development and other developmental processes, it has not been well characterized in sensory neurogenesis. Here we studied the functional role of Notch signaling in the trigeminal ophthalmic (opV) placode, a prime model of sensory neurogenesis. To establish a good spatiotemporal description of Notch pathway genes in the chick trigeminal placode, a stage-specific expression analysis was conducted, showing that expression of most Notch pathway genes and effectors are expressed in the placode, with expression primarily being confined to ectodermal cells. Expression was highest at stages of peak neuronal differentiation. To test the function of Notch signaling in opV placode cell differentiation, Notch receptor cleavage was blocked using the gamma-secretase inhibitor, DAPT, or signaling was activated by misexpression of the Notch intracellular domain (NICD). Notch activation resulted in a significant reduction in sensory neurogenesis. Cells remained in the ectoderm and did not differentiate. Expression of the opV specification marker Pax3 was also lost in targeted cells. DAPT exposure resulted in a dramatic increase in neurogenesis without increasing proliferation, where many differentiated cells were found in the mesenchyme and, surprisingly, within the ectoderm. This is the first result clearly showing prolific neuronal differentiation in the ectoderm of the trigeminal placodes after experimental manipulation of a molecular signaling pathway, thus identifying Notch signaling as a primary regulator of the sensory neuron fate in the opV placode.
三叉神经感觉神经元由神经嵴和神经外胚层发育而来，一直被作为感觉神经元形成的主要模型进行研究。尽管 Notch 途径在中枢神经系统发育和其他发育过程中已得到广泛研究，但在感觉神经发生中尚未得到很好的描述。在这里，我们研究了 Notch 信号在三叉神经眼（opV）神经嵴中的功能作用，这是感觉神经发生的主要模型。为了在鸡三叉神经嵴中建立 Notch 途径基因的良好时空描述，进行了特定于阶段的表达分析，表明大多数 Notch 途径基因和效应物的表达都在神经嵴中，主要局限于外胚层细胞。表达在神经元分化高峰期最高。为了测试 Notch 信号在 opV 神经嵴细胞分化中的功能，使用γ-分泌酶抑制剂 DAPT 阻断 Notch 受体切割，或通过过表达 Notch 细胞内结构域（NICD）激活信号。Notch 激活导致感觉神经元发生显著减少。细胞仍保留在外胚层中且未分化。靶向细胞中 opV 特异性标记物 Pax3 的表达也丢失。DAPT 暴露导致神经发生急剧增加而没有增加增殖，其中许多分化细胞在间充质中发现，令人惊讶的是，在外胚层中也发现了许多分化细胞。这是首次明确表明在三叉神经嵴的外胚层中，通过对分子信号通路的实验操作，可产生丰富的神经元分化，从而将 Notch 信号鉴定为 opV 神经嵴中感觉神经元命运的主要调节因子。
