Suzuki E, Rose D, Chiba A
Department of Fine Morphology, Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, and CREST, JST, Japan.
J Neurobiol. 2000 Mar;42(4):448-59. doi: 10.1002/(sici)1097-4695(200003)42:4<448::aid-neu6>3.0.co;2-h.
During the development of neural networks, what sets synaptogenic interactions apart from nonsynaptogenic interactions is not well understood at the subcellular level. Using a combination of intracellular dye injection and electron microscopy, we show that a specific motoneuron (RP3) and its synaptic partners (muscles 6 and 7), both often bearing microprocesses, develop intimate membrane contact sites characterized by junctional structures, prior to their initiating synaptogenesis in Drosophila embryos. Other motoneuron growth cones that extend alongside the RP3 growth cone to innervate surrounding muscles do not form such contacts with muscles 6 and 7. We also examined how specific target recognition molecules affect the development of these ultrastructural associations between synaptic partner cells. When Fasciclin III (Fas3), a "positive" target recognition molecule for RP3, is ectopically expressed in neighboring muscles, the RP3 growth cone ectopically develops membrane contact sites with Fas3-misexpressing muscles with which it would not normally associate. In contrast, when Toll, a "negative" target recognition molecule normally expressed by a subset of muscles that surrounds muscles 6 and 7, is misexpressed on muscles 6 and 7, the RP3 growth cone fails to exhibit its normal close contact with these muscles. We propose that the formation of close membrane associations and junctional structures can be regulated under the influence of synaptic target recognition molecules and signifies the beginning of subcellular events during synaptic target recognition.
在神经网络发育过程中，在亚细胞水平上，促突触相互作用与非促突触相互作用的区别尚未得到很好的理解。通过结合细胞内染料注射和电子显微镜技术，我们发现果蝇胚胎中，一个特定的运动神经元（RP3）及其突触伙伴（肌肉6和7），两者通常都带有微突起，在开始突触形成之前，就会形成以连接结构为特征的紧密膜接触位点。其他与RP3生长锥一起延伸以支配周围肌肉的运动神经元生长锥，不会与肌肉6和7形成这样的接触。我们还研究了特定的靶标识别分子如何影响突触伙伴细胞之间这些超微结构关联的发育。当Fasciclin III（Fas3），一种RP3的“阳性”靶标识别分子，在邻近肌肉中异位表达时，RP3生长锥会与错误表达Fas3的肌肉异位形成膜接触位点，而它通常不会与这些肌肉发生关联。相反，当Toll，一种通常由围绕肌肉6和7的一部分肌肉表达的“阴性”靶标识别分子，在肌肉6和7上错误表达时，RP3生长锥无法与这些肌肉表现出正常的紧密接触。我们提出，紧密膜关联和连接结构的形成可以在突触靶标识别分子的影响下受到调控，并且标志着突触靶标识别过程中亚细胞事件的开始。
