Mitochondrial membrane tension governs fission

Mitochondria rely on cellular machinery for their division, which is an essential component of metabolic response of the cell. Many division factors have been identified; however, a framework accounting for the energetic requirements of the mitochondrial fission process is lacking. We report that the presence of an active constriction does not ensure fission. Instead, by measuring constrictions down to ~100 nm with time-lapse super-resolution microscopy, we found that 34% of constrictions failed to divide and 9reversed9 to an unconstricted state. Higher local curvatures - reflecting an increased bending energy - made constriction sites more likely to divide, but often with a significant residual energy barrier to fission. Our data suggest that membrane tension, largely arising from pulling forces, could account for this missing energy. These results lead us to propose that mitochondrial fission is probabilistic, and can be modeled as arising from bending energy complemented by a fluctuating membrane tension.