Wright J W, Schwinof K M, Snyder M A, Copenhaver P F
Department of Cell and Developmental Biology L215, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road, Portland, Oregon, 97201, USA.
Dev Biol. 1998 Dec 1;204(1):15-33. doi: 10.1006/dbio.1998.9066.
Neuronal differentiation requires a coordinated intracellular response to diverse extracellular stimuli, but the role of specific signaling mechanisms in regulating this process is still poorly understood. Soluble guanylate cyclases (sGCs), which can be stimulated by diffusible free radical gasses such as nitric oxide (NO) and carbon monoxide (CO) to produce the intracellular messenger cGMP, have recently been found to be expressed within a variety of embryonic neurons and implicated in the control of both neuronal motility and differentiation. Using the enteric nervous system (ENS) of the moth, Manduca sexta, we examined the role of NO and NO-sensitive sGCs during the migration and differentiation of an identified set of migratory neurons (the EP cells). Shortly after the onset of their migration, a subset of EP cells began to express NO-sensitive sGC activity (visualized with an anti-cGMP antiserum). Unlike many neurons in the central nervous system, the expression of sGC activity in the EP cells was not transient but persisted throughout subsequent periods of axon elongation and terminal branch formation on the gut musculature. In contrast, nitric oxide synthase activity (visualized using NADPH-diaphorase histochemistry) was undetectable in the vicinity of the EP cells until the period of synapse formation. Manipulations designed to alter sGC and NOS activity in an in vivo embryonic culture preparation had no discernible effect on either the migration or axonal outgrowth of the EP cells. In contrast, inhibition of both of these enzymes resulted in a significant reduction in terminal synaptic branch formation within the postmigratory neurons. These results indicate that while NO-sensitive sGC activity is expressed precociously within the EP cells during their initial migratory dispersal, a role for this signaling pathway can only be demonstrated well after migration is complete, coincident with the formation of mature synaptic connections.
神经元分化需要细胞内对多种细胞外刺激做出协调反应，但特定信号机制在调节这一过程中的作用仍知之甚少。可溶性鸟苷酸环化酶（sGCs）可被一氧化氮（NO）和一氧化碳（CO）等可扩散自由基气体刺激产生细胞内信使环磷酸鸟苷（cGMP），最近发现其在多种胚胎神经元中表达，并与神经元运动和分化的控制有关。利用烟草天蛾的肠神经系统（ENS），我们研究了NO和对NO敏感的sGCs在一组已确定的迁移神经元（EP细胞）迁移和分化过程中的作用。在它们开始迁移后不久，一部分EP细胞开始表达对NO敏感的sGC活性（用抗cGMP抗血清可视化）。与中枢神经系统中的许多神经元不同，EP细胞中sGC活性的表达不是短暂的，而是在随后的轴突伸长和肠道肌肉组织上的终末分支形成阶段持续存在。相比之下，直到突触形成阶段，在EP细胞附近都检测不到一氧化氮合酶活性（用NADPH-黄递酶组织化学法可视化）。旨在改变体内胚胎培养制剂中sGC和NOS活性的操作对EP细胞的迁移或轴突生长没有明显影响。相反，抑制这两种酶会导致迁移后神经元内终末突触分支形成显著减少。这些结果表明，虽然在EP细胞最初迁移扩散期间，对NO敏感的sGC活性就已早熟表达，但只有在迁移完成后，与成熟突触连接形成同时，才能充分证明该信号通路的作用。
