A Mother’s Sacrifice

Aging determinants are asymmetrically distributed during cell division in S. cerevisiae, which leads to production of an immaculate, age-free daughter cell. During this process, damaged components are sequestered and retained in the mother cell, while higher functioning organelles and rejuvenating factors are transported to and/or enriched in the bud. Here, we will describe the key quality control mechanisms in budding yeast that contribute to asymmetric cell division of aging determinants, with a specific focus on mitochondria. We find that the actin cytoskeleton, which drives transport of many cellular components in yeast, plays a crucial role in segregating fit from less fit mitochondria between mother and daughter cells. Since actin cables are dynamic structures that undergo retrograde flow, treadmilling from the bud towards the mother cell, they acts as filters to prevent damaged, dysfunctional mitochondria from being inherited by the daughter cell. This asymmetry has a direct impact on regulation of daughter cell fitness. A direct counterpart to mitochondrial motility events is anchorage of the organelle, which occurs in the mother tip, mother cortex, and bud tip in budding yeast. We find that mitochondrial fusion, together with tethering protein, serves to promote anchorage and accumulation of mitochondria at the bud tip. This anchorage must be properly maintained, as ectopic increase in mitochondrial anchorage can disrupt quality control mechanisms aimed at promoting asymmetric cell division.