[
International Worm Meeting,
2003]
Respiratory Complex II, or succinate dehydrogenase/fumarate reductase (SDH/FR), of the mitochondrial electron transport chain catalyses either oxidation of succinate under aerobic conditions or reduction of fumarate under microaerobic conditions. The Complex is composed of four polypeptides, Fp, Ip, cybL and cybS. Fp and Ip form the catalytic site while the cyb subunits catalyse electron transport. We chose the Fp subunit for RNA interference (RNAi) studies as it is expected to be a critical component in determining the catalytic function of Complex II. While C. elegans normally lives aerobically, with SDH activity predominating, worms can also survive microaerobic conditions, excreting metabolic end-products indicative of FR activity. We aim to assess which Fp subunit is responsible for FR activity. Three genes encode putative Fp subunits in C. elegans. We silenced the expression of each gene, individually and in combination, using the RNAi feeding method. No obvious phenotype was evident for any gene silenced individually, but simultaneous knockdown of the two closely-related Fp genes (C03G5.1 and C34B2.7) that have high homology to SDH/FR Fp subunits from nematode parasites, induced an 80% decrease in fecundity. The two genes are thus functionally redundant and important under aerobiosis. We also tested worm viability in the presence of sodium azide, an inhibitor of respiratory Complex IV. To date we have observed that silencing expression of the third putative SDH/FR Fp gene (F48E8.3) induced an increased trend in mortality. Further work is planned to identify which gene encodes the Fp subunit catalysing FR activity in the nematode.