A complex II defect affects mitochondrial structure, leading to ced-3- and ced-4-dependent apoptosis and aging.

The mev-1(kn1) mutation of Caenorhabditis elegans is in Cyt-1, which encodes a subunit of succinate-coenzyme Q oxidoreductase in the mitochondrial electron transport chain. Mutants are hypersensitive to oxidative stress and age precociously in part because of increased superoxide anion production. Here, we show that mev-1 mutants are defective in succinate-coenzyme Q oxidoreductase, possess ultrastructural mitochondrial abnormalities (especially in muscle cells), show a loss of membrane potential, have altered CED-9 and Cyt-1 protein levels under hyperoxia, and contain ced-3-and ced-4-dependent supernumerary apoptotic cells. These defects likely explain the failure of mev-1 to complete embryonic development under hyperoxia as well as its reduced life span.