The mitochondrial trans-2-enoyl-CoA reductase is necessary for mitochondrial homeostasis in C. elegans.

Fatty acids function not only as signaling molecules and for energy storage but also as essential cofactors for mitochondrial enzymes. These fatty acid cofactors are produced by the mitochondrial fatty acid synthesis (mtFAS) pathway, the terminal enzyme of which is mitochondrial trans-2-enoyl-CoA reductase (MECR). Dysfunction of MECR prevents the synthesis of fatty acids and is the monogenic cause of Mitochondrial Enoyl-CoA Protein Associated Neurodegeneration (MEPAN) syndrome, a rare mitochondrial disease characterized by dystonia, basal ganglia degeneration, and optic nerve atrophy. Given the necessity of mtFAS products for mitochondrial function, MECR should be essential. Yet, evidence from MEPAN individuals and model organisms with MECR loss of function indicate that mitochondrial function is not as severely impaired as would be expected. However, many of these studies have been limited to single cells or cell types. To better understand the role of MECR and its products in a multicellular system, we used CRISPR/Cas9 to knock out its 2 orthologs in Caenorhabditis elegans, MECR-1 and MECR-2. We found that only MECR-1 is necessary for normal mitochondrial function, germline development, and neuromuscular function. We thus establish a model in which further studies of MECR/MECR-1 can clarify its biochemical, developmental, and physiological roles.