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Immunocytochemical studies of quaking mice support a role for the myelin-associated glycoprotein in forming and maintaining the periaxonal space and periaxonal cytoplasmic collar of myelinating Schwann cells

机译:地震小鼠的免疫细胞化学研究支持髓磷脂相关糖蛋白在形成和维持髓鞘雪旺细胞的轴突间隙和轴突胞质环中的作用

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摘要

The myelin-associated glycoprotein (MAG) is an integral membrane glycoprotein that is located in the periaxonal membrane of myelin- forming Schwann cells. On the basis of this localization, it has been hypothesized that MAG plays a structural role in (a) forming and maintaining contact between myelinating Schwann cells and the axon (the 12-14-nm periaxonal space) and (b) maintaining the Schwann cell periaxonal cytoplasmic collar of myelinated fibers. To test this hypothesis, we have determined the immunocytochemical localization of MAG in the L4 ventral roots from 11-mo-old quaking mice. These roots display various stages in the association of remyelinating Schwann cells with axons, and abnormalities including loss of the Schwann cell periaxonal cytoplasmic collar and dilation of the periaxonal space of myelinated fibers. Therefore, this mutant provides distinct opportunities to observe the relationships between MAG and (a) the formation of the periaxonal space during remyelination and (b) the maintenance of the periaxonal space and Schwann cell periaxonal cytoplasmic collar in myelinated fibers. During association of remyelinating Schwann cells and axons, MAG was detected in Schwann cell adaxonal membranes that apposed the axolemma by 12-14 nm. Schwann cell plasma membranes separated from the axolemma by distances greater than 12-14 nm did not react with MAG antiserum. MAG was present in adaxonal Schwann cell membranes that apposed the axolemma by 12-14 nm but only partially surrounded the axon and, therefore, may be actively involved in the ensheathment of axons by remyelinating Schwann cells. To test the dual role of MAG in maintaining the periaxonal space and Schwann cell periaxonal cytoplasmic collar of myelinated fibers, we determined the immunocytochemical localization of MAG in myelinated quaking fibers that displayed pathological alterations of these structures. Where Schwann cell periaxonal membranes were not stained by MAG antiserum, the cytoplasmic side of the periaxonal membrane was "fused" with the cytoplasmic side of the inner compact myelin lamella and formed a major dense line. This loss of MAG and the Schwann cell periaxonal cytoplasmic collar usually resulted in enlargement of the 12-14-nm periaxonal space and ruffling of the apposing axolemma. In myelinated fibers, there was a strict correlation between the presence of MAG in the Schwann cell periaxonal membrane and (a) maintenance of the 12-14- nm periaxonal space, and (b) presence of the Schwann cell periaxonal cytoplasmic collar.(ABSTRACT TRUNCATED AT 400 WORDS)
机译:髓磷脂相关糖蛋白(MAG)是一种整合膜糖蛋白,位于形成髓磷脂的雪旺氏细胞轴突膜中。基于这种定位,已经假设MAG在以下方面发挥结构性作用:(a)形成并维持髓鞘雪旺细胞与轴突之间的接触(12-14 nm轴突周围空间)和(b)维持雪旺细胞髓鞘纤维的轴突细胞质领。为了验证这一假设,我们确定了MAG在11个月大地震小鼠L4腹侧根中的免疫细胞化学定位。这些根在髓鞘再生的雪旺氏细胞与轴突的结合中显示出不同的阶段,并且异常包括雪旺氏细胞的周围轴突细胞质环的丧失和髓鞘纤维的轴突周围空间的扩张。因此,该突变体提供了观察MAG与(a)髓鞘再生期间轴突空间的形成和(b)维持髓鞘纤维中轴突空间和雪旺细胞膜突周围细胞质环之间的关系的独特机会。在使髓鞘再生的雪旺氏细胞和轴突结合期间,在与轴突相接12-14 nm的雪旺氏细胞轴突膜中检测到MAG。与腋窝分离距离大于12-14 nm的雪旺细胞质膜不与MAG抗血清反应。 MAG存在于轴突雪旺氏细胞膜中,其与轴突之间的距离为12-14 nm,但仅部分包围轴突,因此可能通过使髓鞘重生的雪旺氏细胞活跃地参与轴突的包裹。为了测试MAG在维持髓鞘纤维的轴突空间和Schwann细胞膜突周细胞质环中的双重作用,我们确定了MAG在髓鞘地震纤维中的免疫细胞化学定位,显示了这些结构的病理改变。在施万细胞周围轴膜未被MAG抗血清染色的情况下,周围轴膜的细胞质侧与内部致密髓鞘片的细胞质侧“融合”,并形成一条主要的密集线。 MAG和雪旺氏细胞轴突周围质膜的这种损失通常会导致12-14 nm轴突间隙的扩大和相应的轴突的波纹。在有髓纤维中,在雪旺氏细胞轴突膜中存在MAG与(a)维持12-14 nm轴突间隙和(b)雪旺氏细胞轴突质膜环存在之间存在严格的相关性。截断为400字)

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