Department of Clinical Genetics, UMC Amsterdam, the Netherlands.
Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Vrije Universiteit (VU) Amsterdam, de Boelelaan 1087, 1081 HV Amsterdam, the Netherlands.
Neuron. 2019 Dec 18;104(6):1065-1080.e12. doi: 10.1016/j.neuron.2019.09.015. Epub 2019 Oct 31.
Secretion principles are conserved from yeast to humans, and many yeast orthologs have established roles in synaptic vesicle exocytosis in the mammalian brain. Surprisingly, SEC4 orthologs and their effectors, the exocyst, are dispensable for synaptic vesicle exocytosis. Here, we identify the SEC4 ortholog RAB3 and its neuronal effector, RIM1, as essential molecules for neuropeptide and neurotrophin release from dense-core vesicles (DCVs) in mammalian neurons. Inactivation of all four RAB3 genes nearly ablated DCV exocytosis, and re-expression of RAB3A restored this deficit. In RIM1/2-deficient neurons, DCV exocytosis was undetectable. Full-length RIM1, but not mutants that lack RAB3 or MUNC13 binding, restored release. Strikingly, a short N-terminal RIM1 fragment only harboring RAB3- and MUNC13-interacting domains was sufficient to support DCV exocytosis. We propose that RIM and MUNC13 emerged as mammalian alternatives to the yeast exocyst complex as essential RAB3/SEC4 effectors and organizers of DCV fusion sites by recruiting DCVs via RAB3.
从酵母到人，分泌原理是保守的，许多酵母直系同源物在哺乳动物大脑的突触小泡胞吐作用中发挥了作用。令人惊讶的是，SEC4 直系同源物及其效应物外泌体(exocyst)对于突触小泡胞吐作用是可有可无的。在这里，我们确定 SEC4 直系同源物 RAB3 和其神经元效应物 RIM1 是哺乳动物神经元中神经肽和神经营养因子从致密核心囊泡 (DCV) 释放所必需的分子。四种 RAB3 基因的失活几乎消除了 DCV 的胞吐作用，而 RAB3A 的重新表达恢复了这一缺陷。在 RIM1/2 缺陷神经元中，DCV 胞吐作用无法检测到。全长 RIM1，但不是缺乏 RAB3 或 MUNC13 结合的突变体，恢复了释放。引人注目的是，只有含有 RAB3 和 MUNC13 相互作用结构域的短 N 端 RIM1 片段足以支持 DCV 的胞吐作用。我们提出，RIM 和 MUNC13 作为哺乳动物替代物，取代了酵母外泌体复合物，作为必需的 RAB3/SEC4 效应物和 DCV 融合位点的组织者，通过 RAB3 募集 DCV。
