Ubiquitin drives cilia shortening

Peroxisome inheritance at the right time and place E very yeast cell has numerous peroxi-somes—organelles that metabolize fatty acids— and roughly half are passed on to their daughter cells. Signaling from the bud to the mother cell ensures even peroxisome distribution by controlling the organelles' transport, say Fagarasanu et al. Peroxisomes travel into the bud along actin tracks using the myosin motor Myo2p, which binds to peroxisomes via a specifi c receptor called Inp2p. Cells ramp up Inp2p expression during mitosis, but the receptor only appears on a subset of peroxisomes, potentially selecting them for Myo2p-mediated movement to the bud. Fagarasanu et al. made point mutants in Myo2p that blocked peroxisome transport, and were surprised that Inp2p levels increased until every peroxisome in the mother cell carried the receptor. This suggests that once enough peroxisomes have accumulated in the bud of wild-type cells, a signal is relayed to the mother cell resulting in Inp2p degradation and a halt to further peroxisome transfer. The group also observed this feedback mechanism within the membrane of a single peroxisome: mutants with a solitary large peroxisome that positions itself halfway into the bud lost Inp2p from the half that remained in the mother cell. Thus, both the cell cycle and the distribution of peroxi-somes control Inp2p expression levels to regulate peroxisome inheritance in time and space. The next challenge, says lead author Andrei Fagarasanu, is to work out how cells sense the presence of peroxisomes in the bud and transmit a signal back to the mother cell to trigger Inp2p's degradation. BS A myosin motor dictates the localiza-tion and movement of an organelle that expels excess water from Dictyo-stelium, report Jung et al. To counteract the os-motic stress of an aqueous environment (when it rains, for example), Dictyostelia pump protons into a membranous organelle called the contractile vacuole (CV), generating an osmotic gradient that sucks up extra water from the cytoplasm. The vacuole swells up and fuses with other CVs to form a large bladder that expels the water through brief contact with the plasma membrane. After relieving itself, the bladder rapidly contracts before sending out new CV tubules around the actin-rich cell cortex to begin the cycle again. Jung et al. found that a myosin called MyoJ localizes to CV membranes, and cells lacking the motor no longer accumulated CVs at their edges. Instead, the membranes clumped together in the center of the …