Mammalian mitochondrial genetics , genomics and turnover

Mitochondria are eukaryotic organelle of endosymbiotic origin, specialized in the energy production, among many other various functions. One of the most remarkable features of mitochondrial proteins is that they are encoded by two genomes, located in different cellular compartments: the large majority of mitochondrial proteins being encoded by the nuclear genome, while the mitochondrial genome only encodes 13 polypeptides of the electron transport chain and mitochondrial tRNAs and rRNAs. This chapter first outlines the modern view of the main characteristics of the mitochondrial genome of mammalian cells, sharing number of similarities with bacterial genomes (circular structure, replication, repair systems, organization in nucleoids) and the consequences on mitochondrial genetics (maternal inheritance, polyploidy, hetero/homoplasmy). The second part of the chapter depicts the processes involved in the turnover of this organelle: the biogenesis of the mitochondrial DNA, proteins and lipids, as well as the degradation of the organelle, either by mitophagy or by the protease-dependent mitochondrial quality control. A particular Correspondence/Reprint request: Dr. Patricia Renard, Laboratory of Biochemistry and Cell Biology (URBC) NARILIS (Namur Research Institute for Life Sciences), University of Namur (FUNDP), Belgium E-mail: patsy.renard@fundp.ac.be Patricia Renard et al. 2 attention is paid to the coordination, between the nuclear and the mitochondrial compartments, that maintains the mitochondrial homeostasis, either in the basal state or in response to mitochondrial dysfunction. This is illustrated by the retrograde responses triggeredto enhance mitochondrial biogenesis and/or to increase the mitochondrial quality control in case of mitochondrial unfolded protein responses (mitoUPR).