Peroxisomes track along actin filaments.

The cell may not be as lazy as we first thought. With an organelle that comes in multiple copies, there is always the option of leaving segregation of that organelle to random chance—in most cases each daughter cell will get at least one copy of the organelle. But budding yeast is not prepared to take that risk, especially when growing daughter cells are so much smaller than mature mothers. On page 979, Hoepfner et al. find that yeast cells actively segregate their peroxisomes. The segregation machinery includes actin cables and a specific motor, Myo2p, and the substrate for the segregation is provided by the dynamin Vps1p, which cleaves the peroxisomes into manageable pieces.Hoepfner et al. came to these conclusions after observing the movement of individual GFP-labeled peroxisomes along the cell cortex to the bud neck, bud cortex, and bud tip. Peroxisomes localize along actin cables, and movement requires actin and the myosin Myo2p, and is directed toward actin patches. Somehow the segregation works even in the absence of Vps1p function, when there are only one to three peroxisomes per cell.

Peroxisome movement has been studied before in mammalian cells during interphase, but has been found to be microtubule-dependent. The authors believe that this movement may help the peroxisomes to find their substrates in larger mammalian cells, but that actin-dependent movements may dominate the longer-range segregation behavior in both yeast and mammalian cells. ▪