Lillesaar C, Fried K
Division of Cell Biology, Department of Biomedicine and Surgery, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden.
Neuroscience. 2004;125(1):149-61. doi: 10.1016/j.neuroscience.2004.01.008.
Although neurite attracting factors are present in the developing dental pulp and trigeminal ganglion (TG) axons can respond to such factors, nerve fibres do not enter the tooth pulp until a late developmental stage compared with surrounding tissues supplied by the TG. This suggests that the dental pulp secretes neurite growth inhibitory molecules. Semaphorins represent one group of substances, which can inhibit/repel growing neurites. The aims of the present study were to investigate if dental tissue explants inhibit/repel neurite growth from TGs at some developmental stages in vitro, and if so, to seek evidence for or against a participation of semaphorins in that interaction. By co-culturing mandibular or dental epithelial and mesenchymal tissue explants and TGs in collagen gels, we found that embryonic day 11 (E11) mandibular and E13 dental mesenchymal explants repel neurites from corresponding TGs. Repulsion was replaced by attraction if tissues from late embryonic or early postnatal mice (E17-postnatal day 5) were used. Using semi-quantitative reverse transcription/polymerase chain reaction we showed that a number of semaphorins were expressed by tooth-related mesenchyme collected from embryonic and postnatal mice. The expression of some semaphorins (3A, 3C, 3F, 4F, 5B, 6A, 6B and 6C) was high early in development and then decreased in a temporal pattern that correlated with neurite inhibitory/repulsive effects of dental mesenchyme observed in co-cultures. The expression of other semaphorins increased with development (3B, 4A and 7A), whilst others varied irregularly or remained at a fairly constant level (3E, 4B, 4C, 4D, 4G and 5A). Immunohistochemistry was used to determine if tooth-related nerve fibres possess neuropilins. This revealed that axons surrounding embryonic tooth buds express neuropilin-1, but not neuropilin-2. In postnatal teeth, nerve fibres located within the tooth pulp were immunonegative for neuropilin-1 and neuropilin-2. We conclude that developing mandibular/dental mesenchyme can inhibit/repel neurite growth in vitro. Our results support the hypothesis that semaphorins may be involved in this interaction.
尽管在发育中的牙髓中存在神经突吸引因子，三叉神经节（TG）轴突也能对这些因子作出反应，但与TG所支配的周围组织相比，神经纤维直到发育后期才进入牙髓。这表明牙髓会分泌神经突生长抑制分子。信号素是一类能够抑制/排斥生长中的神经突的物质。本研究的目的是调查牙组织外植体在体外某些发育阶段是否会抑制/排斥来自TG的神经突生长，如果是，寻找支持或反对信号素参与这种相互作用的证据。通过在胶原凝胶中共培养下颌或牙上皮及间充质组织外植体与TG，我们发现胚胎第11天（E11）的下颌和E13的牙间充质外植体排斥来自相应TG的神经突。如果使用来自胚胎后期或出生后早期小鼠（E17 - 出生后第5天）的组织，排斥作用会被吸引所取代。使用半定量逆转录/聚合酶链反应，我们表明从胚胎和出生后小鼠收集的牙相关间充质表达多种信号素。一些信号素（3A、3C、3F、4F、5B、6A、6B和6C）在发育早期表达较高，然后呈时间性下降，这与共培养中观察到的牙间充质的神经突抑制/排斥作用相关。其他信号素的表达随发育增加（3B、4A和7A），而其他信号素则不规则变化或保持在相当恒定的水平（3E、4B、4C、4D、4G和5A）。免疫组织化学用于确定牙相关神经纤维是否具有神经纤毛蛋白。这表明围绕胚胎牙胚的轴突表达神经纤毛蛋白-1，但不表达神经纤毛蛋白-2。在出生后的牙齿中，位于牙髓内的神经纤维对神经纤毛蛋白-1和神经纤毛蛋白-2呈免疫阴性。我们得出结论，发育中的下颌/牙间充质在体外可抑制/排斥神经突生长。我们的结果支持信号素可能参与这种相互作用的假说。
