Condensed and Living Matter Seminar: "Actin dynamics regulate spatial mixing of mitochondria in dividing cells"

Erika Holzbaur (Department of Physiology, University of Pennsylvania Perelman School of Medicine)
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Symmetric cell division requires the even partitioning of genetic information and cytoplasmic contents between daughter cells. While the mechanisms coordinating the replication and segregation of the genome have been extensively explored, the process by which organelles are apportioned remains less well-understood. We have identified multiple cytoplasmic actin assemblies that play distinct but convergent roles in mitochondrial organization in mitosis. First, there is a dense network of subcortical actin cables crisscrossing individual mitochondria in mitotic cells. This meshwork templates 3D-mitochondrial positioning and ensures the equal segregation of mitochondrial mass in cytokinesis. Second, we identified a dynamic wave of actin filaments that reversibly assembles on the surface of mitochondria to direct their motility. Within this wave mitochondria are either confined within branched-actin clouds or propelled by elongated, actin comet tails. Together, clouds and comet tails promote randomly oriented bursts of movement, which, over the duration of mitosis, effectively shuffles subsets of mitochondria in the mother cell to ensure their random and unbiased partitioning between daughter cells.