PAS components are required for timely mitotic exit

Phosphoinositides are evolutionary conserved phospholipid derivatives found in cellular membranes. Each phosphoinositide interacts with specific proteins to perform cellular functions such as membrane trafficking, signal transduction and cytoskeletal organization. Phosphotidylinositol (3,5) Biphosphate (PtdIns(3,5)P2) is the least abundant phosphoinositide derivative in the cell. PtdIns(3,5)P2 deficiency is associated with neurological diseases such as ALS and Charcot-Marie-Tooth Disease. Although PtdIns(3,5)P2 plays roles in membrane trafficking, stress response, vacuole/endolysosome structure/function and transcriptional regulation, no mitotic function has been attributed to PtdIns(3,5)P2. In this thesis we asked whether PtdIns(3,5)P2 has a function in exit from mitosis. We first applied genetic approaches to analyze contribution of PtdIns(3,5)P2 to mitotic exit. We further analysed anaphase duration and actomyosin ring contraction in PtdIns(3,5)P2 deficient cells. We also investigated the localization of Mitotic Exit Network (MEN) components and its regulators in cells lacking PtdIns(3,5)P2. Our genetic analysis demonstrated that PtdIns(3,5)P2 synthesis becomes essential in cells with impaired MEN activity. Consistent with this result, anaphase and actomyosin ring contraction lasted longer in PtdIns(3,5)P2 deficient cells than in wild type cells. Release of the conserved phosphatase Cdc14 (the most downstream component of the MEN) was also delayed in the absence of PtdIns(3,5)P2. Taken together, our results suggest that PtdIns(3,5)P2 synthesis contributes to mitotic exit in budding yeast through yet an unknown mechanism.