Characterizing the transcriptional regulation of let-721, a Caenorhabditis elegans homolog of human electron flavoprotein dehydrogenase.

LET-721 is the Caenorhabditis elegans ortholog of electron-transferring flavoprotein dehydrogenase (ETFDH). We are studying this protein in C. elegans in order to establish a tractable model system for further exploration of ETFDH structure and function. ETFDH is an inner mitochondrial membrane localized enzyme that plays a key role in the beta-oxidation of fatty acids and catabolism of amino acids and choline. ETFDH accepts electrons from at least twelve mitochondrial matrix flavoprotein dehydrogenases via an intermediate dimer protein and transfers the electrons to ubiquinone. In humans, ETFDH mutations result in the autosomal recessive metabolic disorder, multiple acyl-CoA dehydrogenase deficiency. Mutants of let-721 in C. elegans are either maternal effect lethals or semi-sterile. let-721 is transcribed in the pharynx, body wall muscle, hypoderm, intestine and somatic gonad. In addition, the subcellular localization of LET-721 agrees with predictions that it is localized to mitochondria. We identified and confirmed three cis-regulatory sequences (pha-site, rep-site, and act-site). Phylogenetic footprinting of each site indicates that they are conserved between four Caenorhabditis species. The pha-site mapped roughly 1,300 bp upstream of let-721's translational start site and is necessary for expression in pharyngeal tissues. The rep-site mapped roughly 830 bp upstream of the translational start site and represses expression of LET-721 within pharyngeal tissues. The act-site mapped roughly 800 bp upstream of the translational start site and is required for expression within spermatheca, body wall muscle, pharynx, and intestine. Taken together, we find that LET-721 is a mitochondrially expressed protein that is under complex transcriptional controls.