Mitochondrial fission is a highly regulated process that, when disrupted, can alter metabolism, proliferation and apoptosis^1,2,3. Dysregulation has been linked to neurodegeneration^3,4, cardiovascular disease³ and cancer⁵. Key components of the fission machinery include the endoplasmic reticulum⁶ and actin⁷, which initiate constriction before dynamin-related protein 1 (DRP1)⁸ binds to the outer mitochondrial membrane via adaptor proteins^9,10,11, to drive scission¹². In the mitochondrial life cycle, fission enables both biogenesis of new mitochondria and clearance of dysfunctional mitochondria through mitophagy^1,13. Current models of fission regulation cannot explain how those dual fates are decided. However, uncovering fate determinants is challenging, as fission is unpredictable, and mitochondrial morphology is heterogeneous, with ultrastructural features that are below the diffraction limit. Here, we used live-cell structured illumination microscopy to capture mitochondrial dynamics. By analysing hundreds of fissions in African green monkey Cos-7 cells and mouse cardiomyocytes, we discovered two functionally and mechanistically distinct types of fission. Division at the periphery enables damaged material to be shed into smaller mitochondria destined for mitophagy, whereas division at the midzone leads to the proliferation of mitochondria. Both types are mediated by DRP1, but endoplasmic reticulum- and actin-mediated pre-constriction and the adaptor MFF govern only midzone fission. Peripheral fission is preceded by lysosomal contact and is regulated by the mitochondrial outer membrane protein FIS1. These distinct molecular mechanisms explain how cells independently regulate fission, leading to distinct mitochondrial fates.

线粒体裂变是一个高度调节的过程，当被破坏时，可以改变新陈代谢、增殖和细胞凋亡^1,2,3。失调与神经退行性变^3,4、心血管疾病³和癌症⁵相关。裂变机制的关键成分包括内质网⁶和肌动蛋白⁷，它们在动力相关蛋白 1 (DRP1) ^{8通过衔接蛋白9、10、11}与线粒体外膜结合之前开始收缩，以驱动分裂¹². 在线粒体生命周期中，裂变使新线粒体的生物发生和通过线粒体自噬清除功能失调的线粒体成为可能^1,13. 当前的裂变调控模型无法解释这些双重命运是如何决定的。然而，揭示命运决定因素具有挑战性，因为裂变是不可预测的，线粒体形态是异质的，其超微结构特征低于衍射极限。在这里，我们使用活细胞结构照明显微镜来捕捉线粒体动力学。通过分析非洲绿猴 Cos-7 细胞和小鼠心肌细胞中的数百个裂变，我们发现了两种在功能和机制上截然不同的裂变类型。外围的分裂使受损的物质脱落到较小的线粒体中，用于线粒体自噬，而中间区域的分裂导致线粒体的增殖。两种类型均由 DRP1 介导，但内质网和肌动蛋白介导的预收缩和适配器 MFF 仅控制中区裂变。外周裂变之前是溶酶体接触，并由线粒体外膜蛋白 FIS1 调节。这些不同的分子机制解释了细胞如何独立调节裂变，从而导致不同的线粒体命运。