1. Dulbecco-Telethon Institute, Venetian Institute of Molecular Medicine, Via Orus 2, 35129 Padova, Italy
2. Department of Cell Physiology and Metabolism, University of Geneva Medical School, 1 Rue M. Servet, 1211 Geneve, Switzerland

Correspondence to: Luca Scorrano^1,2 Correspondence and requests for materials should be addressed to L.S (Email: lscorrano@dti.telethon.it).

Abstract

Juxtaposition between endoplasmic reticulum (ER) and mitochondria is a common structural feature, providing the physical basis for intercommunication during Ca²⁺ signalling; yet, the molecular mechanisms controlling this interaction are unknown. Here we show that mitofusin 2, a mitochondrial dynamin-related protein mutated in the inherited motor neuropathy Charcot–Marie–Tooth type IIa, is enriched at the ER–mitochondria interface. Ablation or silencing of mitofusin 2 in mouse embryonic fibroblasts and HeLa cells disrupts ER morphology and loosens ER–mitochondria interactions, thereby reducing the efficiency of mitochondrial Ca²⁺ uptake in response to stimuli that generate inositol-1,4,5-trisphosphate. An in vitro assay as well as genetic and biochemical evidences support a model in which mitofusin 2 on the ER bridges the two organelles by engaging in homotypic and heterotypic complexes with mitofusin 1 or 2 on the surface of mitochondria. Thus, mitofusin 2 tethers ER to mitochondria, a juxtaposition required for efficient mitochondrial Ca²⁺ uptake.

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