Ubiquinone is necessary for Caenorhabditis elegans development at mitochondrial and non-mitochondrial sites

Abstract

Ubiquinone (UQ) is a lipid co-factor that is involved in numerous enzymatic processes and is present in most cellular membranes. In particular, UQ is a crucial electron carrier in the mitochondrial respiratory chain. Recently, it was shown that clk-1 mutants of the nematode worm Caenorhabditis elegans do not synthesize UQ9 but instead accumulate demethoxyubiquinone (DMQ9), a biosynthetic precursor of UQ9 (the subscript refers to the length of the isoprenoid side chain). DMQ9 is capable of carrying out the function of UQ9 in the respiratory chain, as demonstrated by the functional competence of mitochondria isolated from clk-1 mutants, and the ability of DMQ9 to act as a co-factor for respiratory enzymes in vitro. However, despite the presence of functional mitochondria, clk-1 mutant worms fail to complete development when feeding on bacteria that do not produce UQ8. Here we show that clk-1 mutants cannot grow on bacteria producing only DMQ8 and that worm coq-3 mutants, which produce neither UQ9 nor DMQ9, arrest development even on bacteria producing UQ8. These results indicate that UQ is required for nematode development at mitochondrial and non-mitochondrial sites and that DMQ cannot functionally replace UQ at those non-mitochondrial sites.