Littleton J T, Bellen H J, Perin M S
Division of Neuroscience, Baylor College of Medicine, Houston, TX 77030.
Development. 1993 Aug;118(4):1077-88. doi: 10.1242/dev.118.4.1077.
Synaptotagmin is a synaptic vesicle-specific integral membrane protein that has been suggested to play a key role in synaptic vesicle docking and fusion. By monitoring Synaptotagmin's cellular and subcellular distribution during development, it is possible to study synaptic vesicle localization and transport, and synapse formation. We have initiated the study of Synaptotagmin's expression during Drosophila neurogenesis in order to follow synaptic vesicle movement prior to and during synapse formation, as well as to localize synaptic sites in Drosophila. In situ hybridizations to whole-mount embryos show that synaptotagmin (syt) message is present in the cell bodies of all peripheral nervous system neurons and many, if not all, central nervous system neurons during neurite outgrowth and synapse formation, and in mature neurons. Immunocytochemical staining with antisera specific to Synaptotagmin indicates that the protein is present at all stages of the Drosophila life cycle following germ band retraction. In embryos, Synaptotagmin is only transiently localized to the cell body of neurons and is transported rapidly along axons during axonogenesis. After synapse formation, Synaptotagmin accumulates in a punctate pattern at all identifiable synaptic contact sites, suggesting a general role for Synaptotagmin in synapse function. In embryos and larvae, the most intense staining is found along two broad longitudinal tracts on the dorsal side of the ventral nerve cord and the brain, and at neuromuscular junctions in the periphery. In the adult head, Synaptotagmin localizes the discrete regions of the neurophil where synapses are predicted to occur. These data indicate that synaptic vesicles are present in axons before synapse formation, and become restricted to synaptic contact sites after synapses are formed. Since a similar expression pattern of Synaptotagmin has been reported in mammals, we propose that the function of Synaptotagmin and the mechanisms governing localization of the synaptic vesicle before and after synapse formation are conserved in invertebrate and vertebrate species. The ability to mark synapses in Drosophila should facilitate the study of synapse formation and function, providing a new tool to dissect the molecular mechanisms underlying these processes.
突触结合蛋白是一种突触小泡特异性整合膜蛋白，有人认为它在突触小泡对接和融合过程中起关键作用。通过监测发育过程中突触结合蛋白的细胞和亚细胞分布，可以研究突触小泡的定位和运输以及突触形成。我们已着手研究果蝇神经发生过程中突触结合蛋白的表达，以便追踪突触形成之前和期间突触小泡的移动情况，并确定果蝇中的突触位点。对整个胚胎进行原位杂交显示，在神经突生长和突触形成期间以及成熟神经元中，突触结合蛋白（syt）的信息存在于所有外周神经系统神经元以及许多（如果不是全部）中枢神经系统神经元的细胞体中。用针对突触结合蛋白的抗血清进行免疫细胞化学染色表明，该蛋白在胚带回缩后的果蝇生命周期的所有阶段均存在。在胚胎中，突触结合蛋白仅短暂地定位于神经元的细胞体，并在轴突形成过程中沿轴突快速运输。突触形成后，突触结合蛋白以点状模式聚集在所有可识别的突触接触位点，表明突触结合蛋白在突触功能中起普遍作用。在胚胎和幼虫中，最强的染色出现在腹神经索和大脑背侧的两条宽阔纵向束以及外周的神经肌肉接头处。在成年头部，突触结合蛋白定位于预计会发生突触的神经纤维离散区域。这些数据表明，突触小泡在突触形成之前就存在于轴突中，并在突触形成后局限于突触接触位点。由于在哺乳动物中也报道了类似的突触结合蛋白表达模式，我们提出，突触结合蛋白的功能以及突触形成前后突触小泡定位的调控机制在无脊椎动物和脊椎动物物种中是保守的。在果蝇中标记突触的能力应有助于突触形成和功能的研究，为剖析这些过程背后的分子机制提供一种新工具。
