Correlated light and electron microscopy illuminates the role of mitochondrial inner membrane remodeling during apoptosis.

In addition to their role in providing ATP for cellular functions via oxidative phosphorylation, mitochondria also play a critical role in initiating and/or regulating apoptosis through the release of proteins such as cytochrome c from intermembrane and intracristal compartments. The mechanism by which these proteins are able to cross the outer mitochondrial membrane has been a subject of controversy. This paper will review some recent results that demonstrate that inner mitochondrial membrane remodeling does occur during apoptosis in HeLa cells but does not appear to be a requirement for release of cytochrome c from intracristal compartments. Inner membrane remodeling does appear to be related to fragmentation of the mitochondrial matrix, and the form of the remodeling suggests a topological mechanism for inner membrane fission and fusion.