Is mitochondrial gene expression coordinated or stochastic?

© 2018 Portland Press Ltd. All rights reserved. Mitochondrial biogenesis is intimately dependent on the coordinated expression of the nuclear and mitochondrial genomes that is necessary for the assembly and function of the respiratory complexes to produce most of the energy required by cells. Although highly compacted in animals, the mitochondrial genome and its expression are essential for survival, development, and optimal energy production. The machinery that regulates gene expression within mitochondria is localised within the same compartment and, like in their ancestors, the bacteria, this machinery does not use membrane-based compartmentalisation to order the gene expression pathway. Therefore, the lifecycle of mitochondrial RNAs from transcription through processing, maturation, translation to turnover is mediated by a gamut of RNA-binding proteins (RBPs), all contained within the mitochondrial matrix milieu. Recent discoveries indicate that multiple processes regulating RNA metabolism occur at once but since mitochondria have a new complement of RBPs, many evolved de novo from nuclear genes, we are left wondering how co-ordinated are these processes? Here, we review recently identified examples of the co-ordinated and stochastic processes that govern the mitochondrial transcriptome. These new discoveries reveal the complexity of mitochondrial gene expression and the need for its in-depth exploration to understand how these organelles can respond to the energy demands of the cell

Fidelity and coordination of mitochondrial protein synthesis in health and disease

The evolutionary acquisition of mitochondria has given rise to the diversity of eukaryotic life. Mitochondria have retained their ancestral α-proteobacterial traits through the maintenance of double membranes and their own circular genome. Their genome varies in size from very large in plants to the smallest in animals and their parasites. The mitochondrial genome encodes essential genes for protein synthesis and has to coordinate its expression with the nuclear genome from which it sources most of the proteins required for mitochondrial biogenesis and function. The mitochondrial protein synthesis machinery is unique because it is encoded by both the nuclear and mitochondrial genomes thereby requiring tight regulation to produce the respiratory complexes that drive oxidative phosphorylation for energy production. The fidelity and coordination of mitochondrial protein synthesis are essential for ATP production. Here we compare and contrast the mitochondrial translation mechanisms in mammals and fungi to bacteria and reveal that their diverse regulation can have unusual impacts on the health and disease of these organisms. We highlight that in mammals the rate of protein synthesis is more important than the fidelity of translation, enabling coordinated biogenesis of the mitochondrial respiratory chain with respiratory chain proteins synthesised by cytoplasmic ribosomes. Changes in mitochondrial protein fidelity can trigger the activation of the diverse cellular signalling networks in fungi and mammals to combat dysfunction in energy conservation. The physiological consequences of altered fidelity of protein synthesis can range from liver regeneration to the onset and development of cardiomyopathy. (Figure presented.)

Fidelity and coordination of mitochondrial protein synthesis in health and disease

The evolutionary acquisition of mitochondria has given rise to the diversity of eukaryotic life. Mitochondria have retained their ancestral α-proteobacterial traits through the maintenance of double membranes and their own circular genome. Their genome varies in size from very large in plants to the smallest in animals and their parasites. The mitochondrial genome encodes essential genes for protein synthesis and has to coordinate its expression with the nuclear genome from which it sources most of the proteins required for mitochondrial biogenesis and function. The mitochondrial protein synthesis machinery is unique because it is encoded by both the nuclear and mitochondrial genomes thereby requiring tight regulation to produce the respiratory complexes that drive oxidative phosphorylation for energy production. The fidelity and coordination of mitochondrial protein synthesis are essential for ATP production. Here we compare and contrast the mitochondrial translation mechanisms in mammals and fungi to bacteria and reveal that their diverse regulation can have unusual impacts on the health and disease of these organisms. We highlight that in mammals the rate of protein synthesis is more important than the fidelity of translation, enabling coordinated biogenesis of the mitochondrial respiratory chain with respiratory chain proteins synthesised by cytoplasmic ribosomes. Changes in mitochondrial protein fidelity can trigger the activation of the diverse cellular signalling networks in fungi and mammals to combat dysfunction in energy conservation. The physiological consequences of altered fidelity of protein synthesis can range from liver regeneration to the onset and development of cardiomyopathy. (Figure presented.)