Fraher J, Dockery P
Department of Anatomy, University College, Cork, Ireland.
J Anat. 1998 Aug;193 ( Pt 2)(Pt 2):195-201. doi: 10.1046/j.1469-7580.1998.19320195.x.
The axon determines whether or not it is myelinated by the Schwann cell. At maturity there is a positive correlation between sheath thickness and axon calibre. This correlation is initially very low or absent, but gradually strengthens during development. This increase could come about because the axon continuously controls Schwann cell myelinating activity, so that a given axon calibre is associated with a particular myelin sheath thickness, an interaction which would entail the Schwann cell continuously monitoring and responding to axon size. This seems unnecessarily complex. This theoretical study shows that the strong correlation between the 2 parameters within a given myelinated fibre population may come about in a much simpler way than outlined above. This is demonstrated by modelling the growth and myelination of a hypothetical population, utilising data from earlier studies on cervical ventral motoneuron axon development. The hypothesis tested shows that the only instructive interactions by the axon on the Schwann cell necessary for the strong correlation between the 2 parameters to emerge are for the initiation of myelination, its continuation and its termination. These could result from a single stimulus being switched on, persisting for a time and being switched off. Under this influence, the Schwann cell is assumed to proceed to form the myelin sheath at a constant rate which it itself inherently determines, in the absence of any quantitative influence exerted by the axon. This continues until the stimulus for myelination ceases to emanate from the axon. The validity of the hypothesis is demonstrated, because the resulting myelin-axon relationships correspond closely to those observed during development.
轴突决定施万细胞是否对其进行髓鞘化。成熟时，髓鞘厚度与轴突直径呈正相关。这种相关性最初很低或不存在，但在发育过程中会逐渐增强。这种增加可能是因为轴突持续控制施万细胞的髓鞘化活动，使得给定的轴突直径与特定的髓鞘厚度相关联，这种相互作用需要施万细胞持续监测并响应轴突大小。这似乎过于复杂。这项理论研究表明，在给定的有髓纤维群体中，这两个参数之间的强相关性可能以一种比上述方式简单得多的方式产生。通过利用早期关于颈腹侧运动神经元轴突发育的研究数据，对一个假设群体的生长和髓鞘化进行建模，证明了这一点。所测试的假设表明，轴突对施万细胞产生这两个参数之间强相关性所必需的唯一指导性相互作用是髓鞘化的起始、持续和终止。这些可能是由一个单一刺激开启、持续一段时间然后关闭导致的。在这种影响下，假设施万细胞以其自身内在决定的恒定速率开始形成髓鞘，而不受轴突的任何定量影响。这种情况会持续到髓鞘化刺激不再从轴突发出。该假设的有效性得到了证明，因为所得到的髓鞘 - 轴突关系与发育过程中观察到的关系密切对应。
