Li J Y, Edelmann L, Jahn R, Dahlström A
Department of Anatomy and Cell Biology, University of Göteborg, Sweden.
J Neurosci. 1996 Jan;16(1):137-47. doi: 10.1523/JNEUROSCI.16-01-00137.1996.
Synaptobrevin, a membrane protein of synaptic vesicles that plays a key role in exocytosis, occurs in two closely related isoforms, synaptobrevin I and II. We have analyzed the axonal transport of both isoforms in sciatic nerve and spinal roots. When fast axonal transport was interrupted by crushing, the proteins accumulated continuously proximal to the crush. Accumulation also was observed distal to the crush, but to a lesser extent (47 and 63% of the proximal accumulation for synaptobrevin I and II, respectively). Immunoelectron microscopy revealed that, proximal to the crush, synaptobrevin I and II were associated with small clear vesicles reminiscent of typical synaptic vesicles. Distal to the crush, membranes positive for synaptobrevin I or II were more heterogeneous, including larger membrane profiles that may represent endosomes. In spinal cord, synaptobrevin I and II were colocalized in many terminals. However, labeling for synaptobrevin I was more intense whereas labeling for synaptobrevin II was stronger in dorsal than in ventral horn terminals. Motor endplates contained only synaptobrevin I. In the sciatic nerve, synaptobrevin I was present predominantly in large, myelinated axons, whereas synoptobrevin II was virtually absent but abundant in small- and medium-sized axons. Lumbar sympathectomy, ventral rhizotomy, and double-labeling studies confirmed that synaptobrevin I is present predominantly in motor neurons whereas synaptobrevin II is present in adrenergic and sensory neurons. We conclude that synaptobrevin I and II are transported bidirectionally by fast axonal transport and are expressed heterogeneously in different neurons in the peripheral nervous system of the adult rat, suggesting that these isoforms have special functional roles in different sets of neurons.
突触小泡蛋白是一种在突触小泡中发挥关键作用的膜蛋白，它在胞吐作用中起关键作用，有两种密切相关的同工型，即突触小泡蛋白I和II。我们分析了坐骨神经和脊神经根中这两种同工型的轴突运输情况。当快速轴突运输因挤压而中断时，这些蛋白质在挤压点近端持续积累。在挤压点远端也观察到了积累，但程度较轻（突触小泡蛋白I和II分别为近端积累的47%和63%）。免疫电子显微镜显示，在挤压点近端，突触小泡蛋白I和II与类似于典型突触小泡的小清亮小泡相关。在挤压点远端，突触小泡蛋白I或II阳性的膜更为异质，包括可能代表内体的较大膜结构。在脊髓中，突触小泡蛋白I和II在许多终末中共定位。然而，突触小泡蛋白I的标记更强烈，而突触小泡蛋白II在背角终末的标记比腹角终末更强。运动终板仅含有突触小泡蛋白I。在坐骨神经中，突触小泡蛋白I主要存在于大型有髓轴突中，而突触小泡蛋白II几乎不存在，但在中小型轴突中丰富。腰交感神经切除术、腹侧神经根切断术和双标记研究证实，突触小泡蛋白I主要存在于运动神经元中，而突触小泡蛋白II存在于肾上腺素能和感觉神经元中。我们得出结论：突触小泡蛋白I和II通过快速轴突运输双向运输，并且在成年大鼠外周神经系统的不同神经元中异质表达，这表明这些同工型在不同的神经元组中具有特殊的功能作用。
