Hering H, Kröger S
Department of Neuroanatomy, Max-Planck-Institute for Brain Research, Frankfurt, Germany.
J Comp Neurol. 1996 Nov 18;375(3):393-405. doi: 10.1002/(SICI)1096-9861(19961118)375:3<393::AID-CNE4>3.0.CO;2-Y.
The development of synapse-like specializations was investigated in the inner plexiform layer of the developing chick retina by using light and electron microscopy. Six monoclonal antibodies, directed against glycine and gamma-aminobutyric acid (GABA)A receptor subunits, the intracellular receptor-associated protein gephyrin, synaptotagmin, and synaptophysin were used to determine the initial appearance and distribution of their antigens. Synaptophysin and synaptotagmin immunoreactivity was detected in the retina concurrent with the formation of the inner plexiform layer at embryonic day 7. This early appearance before synaptic differentiation, together with the transient expression of synaptotagmin immunoreactivity in the synapse-free optic fiber layer, suggests that in the developing central nervous system (CNS) these proteins are not confined to synapses. The first immunofluorescence signal detected with specific antibodies against the beta 2 and beta 3-subunits of the GABAA receptor, the glycine receptor, and gephyrin appeared at embryonic day 12. In contrast, the alpha 1-subunit of the adult-type glycine receptor heteromeric complex was detectable only at later stages of development, after embryonic day 16, suggesting a change in the subunit composition of some glycine receptor complexes. The staining was clearly punctate, indicating the clustering of the alpha 1-subunit at synapses. Electron microscopic investigation revealed the first postsynaptic densities and active zones in the inner plexiform layer of the retina at embryonic day 12. These results reveal different patterns of development for the investigated pre- and postsynaptic proteins and indicate a parallel appearance of gephyrin, glycine receptor, and the beta 2 and beta 3-subunits of the GABAA receptor with the first synaptic specializations in the inner plexiform layer of the developing chick retina.
通过光学显微镜和电子显微镜，对发育中的雏鸡视网膜内网状层中突触样特化结构的发育进行了研究。使用了六种单克隆抗体，分别针对甘氨酸和γ-氨基丁酸（GABA）A受体亚基、细胞内受体相关蛋白gephyrin、突触结合蛋白和突触小泡蛋白，以确定其抗原的初始出现和分布情况。在胚胎第7天，随着内网状层的形成，视网膜中检测到了突触小泡蛋白和突触结合蛋白的免疫反应性。这种在突触分化之前的早期出现，以及在无突触的视神经纤维层中突触结合蛋白免疫反应性的短暂表达，表明在发育中的中枢神经系统（CNS）中，这些蛋白质并不局限于突触。用针对GABAA受体的β2和β3亚基、甘氨酸受体和gephyrin的特异性抗体检测到的第一个免疫荧光信号出现在胚胎第12天。相比之下，成年型甘氨酸受体异聚体复合物的α1亚基仅在胚胎第16天之后的发育后期才能检测到，这表明一些甘氨酸受体复合物的亚基组成发生了变化。染色明显呈点状，表明α1亚基在突触处聚集。电子显微镜研究显示，在胚胎第12天，视网膜内网状层中出现了第一批突触后致密物和活性区。这些结果揭示了所研究的突触前和突触后蛋白质不同的发育模式，并表明gephyrin、甘氨酸受体以及GABAA受体的β2和β3亚基与发育中的雏鸡视网膜内网状层中第一批突触特化结构同时出现。
