The distinct activities of organelles depend on the proper function of their membranes. Coordinated membrane biogenesis of different organelles necessitates lipid transport from their site of synthesis to their destination. Several factors have been proposed to participate in lipid distribution, but despite its basic importance, in vivo evidence linking the absence of putative transport pathways to specific transport defects remains scarce. A reason for this scarcity is the near absence of in vivo lipid trafficking assays. Here we introduce a versatile method named METALIC (Mass tagging-Enabled TrAcking of Lipids In Cells) to track interorganelle lipid flux inside cells. In this strategy, two enzymes, one directed to a ‘donor’ and the other to an ‘acceptor’ organelle, add two distinct mass tags to lipids. Mass-spectrometry-based detection of lipids bearing the two mass tags is then used to quantify exchange between the two organelles. By applying this approach, we show that the ERMES and Vps13–Mcp1 complexes have transport activity in vivo, and unravel their relative contributions to endoplasmic reticulum–mitochondria lipid exchange.

细胞器的不同活动取决于其膜的正常功能。不同细胞器的协调膜生物发生需要脂质从它们的合成位点转运到它们的目的地。已经提出了几个参与脂质分布的因素，但尽管其基本重要性，但将假定的运输途径的缺乏与特定运输缺陷联系起来的体内证据仍然很少。这种稀缺的一个原因是几乎没有体内脂质运输检测。在这里，我们介绍了一种名为 METALIC（质量标记启用的细胞内脂质追踪）的多功能方法，用于追踪细胞内细胞器间的脂质通量。在这个策略中，两种酶，一种针对“供体”，另一种针对“受体”细胞器，将两个不同的质量标签添加到脂质中。然后使用基于质谱法的带有两个质量标签的脂质检测来量化两个细胞器之间的交换。通过应用这种方法，我们表明 ERMES 和 Vps13–Mcp1 复合物在体内具有转运活性，并揭示了它们对内质网-线粒体脂质交换的相对贡献。