Vacuole membrane homeostasis

How do cells measure the size of their organelles? Vacuoles form by fusing with endosomes and other vesicles.

We favor the idea that the ratio of two lipids, PI3P on endosomes (phosphatidylinositol-3-phosphate) and its dually phosphorylated cousin PI(3,5)P2 at endosomes and vacuoles are particularly important. These lipids bind proteins and recruit them or change their activity on membranes.

We identified that a particular regulator, called Ivy1 (tagged with GFP in the cells above), localizes to distinct endosomes called signaling endosome. These are different from so called late endosomes or multivesicular bodies, here marked by the ESCRT-subunit Vps4. Signaling endosomes have the nutrient sensing kinase TORC1 on their surface, though we do not understand, what their particular function is. We are now focussing on the biogenesis of signaling endosomes and in this context how they control vacuole size and function.