Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322.
Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322.
eNeuro. 2017 Aug 10;4(4). doi: 10.1523/ENEURO.0232-17.2017. eCollection 2017 Jul-Aug.
The neuromuscular junction (NMJ) is a chemical synapse formed between motoneurons and skeletal muscle fibers. The vertebrate NMJ uses acetylcholine (ACh) as the neurotransmitter and features numerous invaginations of the postsynaptic muscle membrane termed junctional folds. ACh receptors (AChRs) are believed to be concentrated on the crest of junctional folds but their spatial organization remains to be fully understood. In this study, we utilized super-resolution microscopy to examine the nanoscale organization of AChRs at NMJ. Using Structured Illumination Microscopy, we found that AChRs appear as stripes within the pretzel-shaped mouse NMJs, which however, do not correlate with the size of the crests of junctional folds. By comparing the localization of AChRs with several pre- and postsynaptic markers of distinct compartments of NMJs, we found that AChRs are not distributed evenly across the crest of junctional folds as previously thought. Instead, AChR stripes are more closely aligned with the openings of junctional folds as well as with the presynaptic active zone. Using Stochastic Optical Reconstruction Microscopy (STORM) for increased resolution, we found that each AChR stripe contains an AChR-poor slit at the center that is equivalent to the size of the opening of junctional folds. Together, these findings indicate that AChRs are largely localized to the edges of crests surrounding the opening of folds to align with the presynaptic active zones. Such a nanoscale organization of AChRs potentially enables trans-synaptic alignment for effective synaptic transmission of NMJs.
神经肌肉接头(NMJ)是运动神经元和骨骼肌纤维之间形成的化学突触。脊椎动物 NMJ 使用乙酰胆碱(ACh)作为神经递质,并具有大量的突触后肌膜内陷,称为连接褶皱。ACh 受体(AChRs)被认为集中在连接褶皱的峰顶上,但它们的空间组织仍有待充分了解。在这项研究中,我们利用超分辨率显微镜检查 NMJ 处 AChR 的纳米级组织。使用结构照明显微镜,我们发现 AChR 出现在呈椒盐卷饼形状的小鼠 NMJ 内的条纹中,但与连接褶皱峰的大小无关。通过将 AChR 的定位与 NMJ 不同隔间的几个前和后突触标记物进行比较,我们发现 AChR 不像以前认为的那样均匀分布在连接褶皱的峰顶上。相反,AChR 条纹更紧密地与连接褶皱的开口以及突触前活性区对齐。使用随机光学重建显微镜(STORM)提高分辨率,我们发现每个 AChR 条纹在中心都包含一个 AChR 贫乏的狭缝,其大小相当于连接褶皱的开口。总之,这些发现表明 AChR 主要定位于围绕褶皱开口的峰的边缘,以与突触前活性区对齐。AChR 的这种纳米级组织可能使跨突触对齐,从而有效地进行 NMJ 的突触传递。