Ahnert-Hilger G, Kutay U, Chahoud I, Rapoport T, Wiedenmann B
Medizinische Klinik und Poliklinik, Abt. Gastroenterologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Germany.
Eur J Cell Biol. 1996 May;70(1):1-11.
The formation of small synaptic vesicles represents a hallmark during synaptogenesis. The small synaptic vesicle protein synaptophysin is considered as a marker protein for synapses during neuronal development. Another small synaptic vesicle protein, synaptobrevin, is now well accepted to play an important role for the function of synapses in being a key component of exocytosis. Its role during synaptogenesis is not known. Tetanus toxin which exclusively proteolysis synaptobrevin thereby inhibiting secretion from all types of neurons was used to investigate consequences of inactivating synaptobrevin for the formation of small synaptic vesicles and synaptic contacts. In primary cultures of mouse hypothalamic and cerebellar neurons cultivated for 3 to 4 days, synaptobrevin appears earlier on small synaptic vesicles and in synaptic contacts than synaptophysin. Upon longer cultivation up to 12 to 14 days in vitro both proteins associated equally with small synaptic vesicles. Interestingly, GABA secretion stimulated by 50 mM potassium or 500 PM alpha-latrotoxin, did not vary during cultivation time. Tetanus toxin added to neuronal cultures at day 2 in vitro cleaved synaptobrevin and inhibited regulated GABA secretion during the whole cultivation time. Despite the impaired function of synaptobrevin other synaptic proteins such as synaptophysin, synaptotagmin, rab 3A, protein SV2, SNAP-25 and syntaxin were found in processes and synaptic contacts comparable to untreated cultures. The expression of various synaptic proteins was also followed in vivo. In mouse brains taken at different embryonic days, synaptobrevin, synaptotagmin, rab 6 and the membrane protein SNAP-25 were expressed earlier than synaptophysin and protein SV2. We conclude that synaptobrevin represents a marker for early events in synaptogenesis. Its proteolysis by tetanus toxin, however, does not interfere with the formation of synaptic contacts and neuronal differentiation.
小突触囊泡的形成是突触发生过程中的一个标志。小突触囊泡蛋白突触素被认为是神经元发育过程中突触的标记蛋白。另一种小突触囊泡蛋白突触结合蛋白，现在已被广泛接受在作为胞吐作用的关键成分对突触功能中发挥重要作用。其在突触发生过程中的作用尚不清楚。破伤风毒素专门裂解突触结合蛋白从而抑制所有类型神经元的分泌，被用于研究使突触结合蛋白失活对小突触囊泡形成和突触接触的影响。在培养3至4天的小鼠下丘脑和小脑神经元原代培养物中，突触结合蛋白比突触素更早出现在小突触囊泡和突触接触中。在体外培养长达12至14天时，两种蛋白与小突触囊泡的结合程度相同。有趣的是，由50 mM钾或500 μMα-银环蛇毒素刺激的GABA分泌在培养期间没有变化。在体外第2天添加到神经元培养物中的破伤风毒素裂解突触结合蛋白并在整个培养期间抑制调节性GABA分泌。尽管突触结合蛋白功能受损，但在突起和突触接触中发现了其他突触蛋白，如突触素、突触结合蛋白、rab 3A、蛋白SV2、SNAP-25和 syntaxin，与未处理的培养物相当。还在体内追踪了各种突触蛋白的表达。在不同胚胎期获取的小鼠大脑中，突触结合蛋白、突触结合蛋白、rab 6和膜蛋白SNAP-25的表达早于突触素和蛋白SV2。我们得出结论，突触结合蛋白代表突触发生早期事件的一个标记。然而，破伤风毒素对其的蛋白水解并不干扰突触接触的形成和神经元分化。
