首页> 外文期刊>Journal of Neurocytology: A Journal of Cellular Neurobiology >Snap-25 is polarized to axons and abundant along the axolemma: an immunogold study of intact neurons.
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Snap-25 is polarized to axons and abundant along the axolemma: an immunogold study of intact neurons.

机译:Snap-25被极化为轴突并沿轴突丰富:完整神经元的免疫金研究。

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摘要

SNAP-25, synaptosomal associated protein of 25 kDa, is reported to be a t-SNARE (target receptor associated with the presynaptic plasma membrane) involved in the docking and fusion of synaptic vesicles. We present here the first ultrastructural localization of SNAP-25 in intact neurons by pre-embedding EM immunocytochemistry in rat brains, hippocampal slice cultures, and PC12 cells. In differentiated neurons, SNAP-25 labeling was clearly membrane-associated. The labeling was most prominent in the plasma membrane of axons and excluded from the plasma membranes of soma and dendrites. Furthermore, SNAP-25 did not appear to be restricted to the synaptic junctions. SNAP-25 labeling was seen in the cytoplasm of the soma and large dendrites, mostly associated with the Golgi complexes. There were also some SNAP-25 labeled tubulo-vesicular structures in the cytoplasm of the soma and the axons, but rarely in the smaller dendrites. In PC12 cells, after 5-10 minutes of high potassium (75 mM) stimulation in the presence of HRP, SNAP-25 labeling appeared, additionally, on HRP-filled early endosomes. After a longer (20-30 minutes) HRP incubation, most of the later stage endosomes and lysosomes were loaded with HRP but they were negative for SNAP-25. These results suggest that SNAP-25 is sorted out of these late endosomal compartments, and that the bulk of the SNAP-25 protein is probably recycled back to the axolemma from the early endosomes. In contrast, in those samples which were incubated with HRP for longer periods, there were still some SNAP-25-positive vesicular structures which were HRP-negative. These structures most likely represent anterograde vesicles that carry newly synthesized SNAP-25 from the soma to the axolemma by axonal transport. SNAP-25 appears to be sorted at the Golgi complex to reach the axolemma specifically. Its widespread distribution all along the axolemma does not support the view of SNAP-25 as a t-SNARE limited for synaptic exocytosis.
机译:SNAP-25,25kDa的突触体相关蛋白,据报道是参与突触小泡对接和融合的t-SNARE(与突触前质膜相关的靶受体)。我们在这里通过预先嵌入大鼠脑,海马切片培养和PC12细胞中的EM免疫细胞化学,在完整的神经元中展示SNAP-25的第一个超微结构定位。在分化的神经元中,SNAP-25标记明显与膜相关。标记在轴突的质膜中最突出,而从体细胞和树突的质膜中排除。此外,SNAP-25似乎不限于突触连接。 SNAP-25标记见于体细胞和大树突的细胞质中,大多数与高尔基复合体有关。在体细胞和轴突的细胞质中也有一些SNAP-25标记的肾小管水泡结构,但在较小的树突中很少。在PC12细胞中,在HRP存在下高钾(75 mM)高刺激5-10分钟后,SNAP-25标记也出现在充满HRP的早期内体上。在较长时间(20-30分钟)的HRP孵育后,大多数后期的内体和溶酶体均装有HRP,但它们对SNAP-25呈阴性。这些结果表明,SNAP-25是从这些晚期的内体区室中分选出来的,并且大部分SNAP-25蛋白可能从早期的内体循环回到了轴索中。相反,在那些与HRP孵育时间较长的样品中,仍然存在一些HRP阴性的SNAP-25阳性囊泡结构。这些结构最有可能代表顺行囊泡,其通过轴突运输将新合成的SNAP-25从体细胞携带到轴突。 SNAP-25似乎是在高尔基复合体上分选的,专门到达了轴索。它在整个腋窝中的广泛分布并不支持SNAP-25作为限制突触胞吐作用的t-SNARE的观点。

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