Mitochondrial Biology: RNA Import and Xenomitochondrial Compensatory Mechanisms

Abstract

Deficiencies or alterations in mitochondrial function can cause or exacerbate many human diseases, including metabolic and developmental disorders. The first experiments described herein were conducted to study compensatory mechanisms for mitochondrial inefficiencies. Xenomitochondrial mice, harboring evolutionarily divergent Mus terricolor mitochondrial DNA (mtDNA) on a Mus musculus domesticus nuclear background, were characterized phenotypically. Lack of in vivo phenotype indicative of mitochondrial dysfunction in xenomitochondrial mice contrasted mitochondrial dysfunction observed in in vitro xenomitochondrial cybrid studies. Genetic studies revealed that the only genes involved in energy production with expression changes in xenomitochondrial mice were encoded by the mtDNA. Results illustrate that compensatory mechanisms for mild mitochondrial inefficiencies alter mtDNA gene expression without altering expression patterns of nuclear encoded genes involved in mitochondrial energy production. Understanding these mechanisms will facilitate development of therapeutic interventions for mitochondrial disorders. Experiments described subsequent to xenomitochondrial characterization explored mechanisms whereby specific RNAs are imported into mitochondria. Characterization of mitochondrial RNA import mechanisms may allow development of gene therapy to treat devastating mitochondrial diseases. RNA affinity purification identified proteins that interact selectively with imported RNAs from both cellular and mitochondrial lysates. RNA immunoprecipitation (RIP) did not confirm protein:RNA interactions due to large variability in results. The cytoplasmic roles of proteins identified by RNA affinity purification studies shed light on specific mechanisms of mitochondrial RNA import. Additionally, sequencing of mitochondrial RNA revealed several novel RNAs associated with mitochondria. These RNAs are uncharacterized and future studies will reveal the biological significance of their association with mitochondria.