The yeast cell cortical protein Num1 integrates mitochondrial dynamics into cellular architecture.

During the cell cycle each organelle has to be faithfully partitioned to the daughter cells. However, the mechanisms controlling organellar inheritance remain poorly understood. We studied the contribution of the cell cortex protein, Num1, to mitochondrial partitioning in yeast. Live-cell microscopy revealed that Num1 is required for attachment of mitochondria to the cell cortex and retention in mother cells. Electron tomography of anchoring sites revealed plasma membrane invaginations directly contacting the mitochondrial outer membrane. Expression of chimeric plasma membrane tethers rescued mitochondrial fission defects in Δnum1 and Δmdm36 mutants. These findings provide new insights into the coupling of mitochondrial dynamics, immobilization, and retention during inheritance.