Without Inp1p (bottom), all peroxisomes are transported into the bud.

In the field of organelle inheritance, peroxisomes are the forgotten stepchild no more. Fagarasanu et al. (page 765) find that a previously uncharacterized protein, Inp1p, tethers a fraction of the peroxisomes to the cortex of the mother cell during bud formation in S. cerevisiae. Cells lacking Inp1p lose almost all peroxisomes to the bud.

Yeast cells are known to actively partition organelles between the mother and bud during division. Mitochondria, for example, are subjected to both retention and ordered movement to ensure that a proper fraction of the organelles end up in each cell after cytokinesis. In the case of peroxisomes, researchers knew that a subset of the organelles moved into the bud in a myosin-dependent manner, but a retention mechanism hadn't been detected.Inp1p was putatively localized to the peroxisome based on genome-wide GFP tagging efforts conducted several years ago. The current study confirmed Inp1p's location and defined it as a peripheral peroxisomal membrane protein. It associated with proteins known to influence peroxisome size and shape.

Video microscopy of wild-type cells showed peroxisomes moving in a directed manner to the bud. Mother cells lacking Inp1p retain few of the peroxisomes, most of which move to the growing bud tip. In cells overexpressing Inp1p, peroxisomes were tightly associated with the cortical regions of mother cells, and buds developed with few or no peroxisomes.

Movement of excess peroxisomes to the bud in cells lacking Inp1p may be due to a decreased affinity of peroxisomes for some cortical anchor in the mother cell. But what that anchor is or how Inp1p attaches to it is unclear.