Abstract:
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Mitochondria are dynamic organelles that represent a single cellular compartment interconnected by continuous fusion and fission. The balance of these antagonizing reactions determines overall mitochondrial morphology, which ranges from elongated branched filaments to small punctuate structures. During mitosis organelles like nucleus, Golgi apparatus and endoplasmic reticulum are dramatically rearranged and rearrangements are required for progression of cell division. In contrast, little is known about the mitochondrial inheritance, which not only ensures the transmission of organelles’ membranes and proteins, but also that of the mitochondrial DNA (mtDNA), which encodes essential components of the respiratory chain as well as RNA molecules required for their intramitochondrial translation. This genome is organised in hundreds of nucleoids, nucleoprotein complexes containing 2-8 copies of mtDNA that distribute throughout mitochondria. Transmission of this mtDNA is essential to understand the appearance and transmission of severe, maternally transmitted mitochondrial diseases provoked by mtDNA mutations. In this work, we focus on evolution of mitochondrial morphology and associated mtDNA nucleoids transmission during mitosis, which we investigate in mitotic HeLa cells. We show that, in contrast to the fragmenting Golgi apparatus, mitochondria retain their filamentous morphology throughout mitosis. Mitochondria are excluded from the area occupied by chromosomes and the mitotic spindle, but distribute homogenously throughout dividing cells. We show that the majority of filamentous mitochondria contain numerous mtDNA-nucleoids and that nucleoids distribute, like mitochondria, throughout the dividing cell. Finally we show that Drp1-mediated mitochondrial fission is not essential for mitochondrial transmission, progression though mitosis and cytokinesis.
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