Twinkle is not the mitochondrial DNA replicative helicase in C. elegans, but may have alternate mitochondrial functions

Abstract

Twinkle is not the mtDNA helicase in C. elegans 17 ABSTRACT 26 27 Dysfunction of mitochondrial DNA replication machinery is a common cause of mitochondrial 28 diseases. The minimal mammalian replisome is made up of DNA polymerase gamma, replicative 29 helicase Twinkle, and single-stranded DNA binding protein. The replisome is localized to the 30 inner mitochondrial membrane and serves as the site of mitochondrial DNA replication and 31 mitochondrial fission. Recently, a sequence homolog of Twinkle was uncovered in the nematode 32 Caenorhabditis elegans. Here, we characterized this homolog, twnk-1, and report that twnk-1 33 does not function as the primary mitochondrial DNA replicative helicase in this species, as loss 34 of twnk-1 does not result in reduce mitochondrial DNA levels, or result in other expected 35 mitochondrial dysfunctions such as reduced oxygen consumption rates, increased sensitivity to 36 metabolic perturbations, or reduced muscle function. Instead, twnk-1 mutants have increased 37 mitochondrial DNA as they age, and exhibit phenotypes associated with mitochondrial stress, 38 including reduced fecundity, an activation of the mitochondrial unfolded protein response, and 39 mitochondrial fragmentation. Our results suggest in Caenorhabditis elegans, twnk-1 does not 40 function as the mitochondrial DNA replicative helicase, but has an alternative function in 41 regulating mitochondrial function. 42 43 45Mitochondria are essential organelles, responsible for cellular energy production and 46 the synthesis of metabolites in metazoa. They are the site of β-oxidation of fatty acids and 47 oxidative phosphorylation, have essential roles in calcium homeostasis and apoptosis, and drive 48 anabolic biosynthesis events that support cellular growth. Aberrant mitochondrial function can 49 trigger a wide range of metabolic consequences, and mitochondrial dysfunction is associated 50 with numerous diseases (Gorman et al.