Pinçon-Raymond M, Murawsky M, Mege R M, Rieger F
UA 614 CNRS, U. 153 INSERM, Paris, France.
Dev Biol. 1987 Nov;124(1):259-68. doi: 10.1016/0012-1606(87)90477-5.
In the muscular dysgenic (mdg/mdg) mouse embryo, both muscle and nerve are affected early during embryogenesis, from Embryonic Day 13 (E13). We now find that the mutation affects not only the degree of differentiation of the muscle and the pattern of motor innervation but also the relationship between Schwann cell and axon. We studied the sciatic nerve of normal and mdg/mdg embryos between E13 and E18 at the ultrastructural level. We found that in mdg/mdg nerve, (1) Schwann cells do not totally enwrap the growing axons in their most distal part, close to the growth cone, and (2) the terminal Schwann cells do not correctly surround the nerve endings and seal the corresponding synaptic contacts. Moreover, both types of mutant Schwann cell lack a normal electron-dense basal lamina. We found that there is an excess of axons relative to the Schwann cell population in the intramuscular portions of the mdg/mdg sciatic nerve. Our observations point toward a possible defect of the mechanism of migration and maturation of Schwann cells. Such a defect may in turn affect primarily or secondarily the mutual influences between Schwann cell and axon and lead to some or all of the major abnormalities observed in the mdg/mdg neuromuscular system, namely, multifocal polyinnervation, immature axon-myotube contacts, and abnormal T-tubule-sarcoplasmic reticulum junctions.
在肌肉发育不全（mdg/mdg）小鼠胚胎中，从胚胎第13天（E13）起，肌肉和神经在胚胎发生早期就受到影响。我们现在发现，该突变不仅影响肌肉的分化程度和运动神经支配模式，还影响施万细胞与轴突之间的关系。我们在超微结构水平上研究了E13至E18正常和mdg/mdg胚胎的坐骨神经。我们发现，在mdg/mdg神经中，（1）施万细胞在最远端靠近生长锥的部分并没有完全包裹生长中的轴突，（2）终末施万细胞没有正确地围绕神经末梢并封闭相应的突触接触。此外，这两种类型的突变施万细胞都缺乏正常的电子致密基膜。我们发现在mdg/mdg坐骨神经的肌内部分，相对于施万细胞群体，轴突数量过多。我们的观察结果表明施万细胞迁移和成熟机制可能存在缺陷。这种缺陷可能继而直接或间接影响施万细胞与轴突之间的相互影响，并导致在mdg/mdg神经肌肉系统中观察到的部分或全部主要异常，即多灶性多神经支配、未成熟的轴突 - 肌管接触以及异常的横管 - 肌浆网连接。
