MICOS assembly controls mitochondrial inner membrane remodeling and crista junction redistribution to mediate cristae formation

Mitochondrial function is critically dependent on the folding of the mitochondrial inner membrane into cristae; indeed, numerous human diseases are associated with aberrant crista morphologies. With the MICOS complex, OPA1 and the F 1 F o ‐ATP synthase, key players of cristae biogenesis have been identified, yet their interplay is poorly understood. Harnessing super‐resolution light and 3D electron microscopy, we dissect the roles of these proteins in the formation of cristae in human mitochondria. We individually disrupted the genes of all seven MICOS subunits in human cells and re‐expressed Mic10 or Mic60 in the respective knockout cell line. We demonstrate that assembly of the MICOS complex triggers remodeling of pre‐existing unstructured cristae and de novo formation of crista junctions (CJs) on existing cristae. We show that the Mic60‐subcomplex is sufficient for CJ formation, whereas the Mic10‐subcomplex controls lamellar cristae biogenesis. OPA1 stabilizes tubular CJs and, along with the F 1 F o ‐ATP synthase, fine‐tunes the positioning of the MICOS complex and CJs. We propose a new model of cristae formation, involving the coordinated remodeling of an unstructured crista precursor into multiple lamellar cristae. Synopsis Biogenesis of mitochondrial cristae is essential for the metabolic function of mitochondria. Super‐resolution light microscopy and 3D‐electron microscopy reveal that assembly of the MICOS complex controls the distribution of crista junctions and lamellar cristae formation. Mic60 and Mic10 subcomplexes have distinct functions in crista junction establishment and cristae formation. Aberrant cristae in MICOS‐deficient mitochondria re‐attach to the mitochondrial inner membrane and convert into lamellar cristae upon re‐expression of MICOS. Interplay between MICOS subcomplexes, OPA1, and the F 1 F o ‐ATP synthase controls size and distribution of MICOS assemblies. A new model of cristae formation suggests that the assembly of the MICOS holo‐complex mediates the remodelling and segmentation of the mitochondrial inner membrane. Graphical Abstract Super‐resolution light microscopy and 3D‐electron microscopy reveal that assembly of the MICOS complex controls the distribution of crista junctions and lamellar cristae formation.