Cell Size In The Membrane: Lipid-dependent signals link mitotic entry to membrane growth
In budding yeast, cell cycle progression and ribosome biogenesis are dependent upon plasma membrane growth, which ensures that events of cell growth are coordinated with each other and with the cell cycle. However, the signals that link the cell cycle and ribosome biogenesis to membrane growth are poorly understood. Our results suggest that membrane trafficking events required for membrane growth are linked to sphingolipid-dependent signaling. Growth requires delivery of sphingolipids in order to couple growth with the cell cycle. A conserved signaling network plays an essential role in sphingolipid signaling by responding to delivery of sphingolipids to the plasma membrane. Sphingolipid-dependent signals control protein kinase C (Pkc1), which plays an essential role in the pathways that link the cell cycle and ribosome biogenesis to membrane growth. Phosphorylation of Pkc1 is dependent upon and proportional to membrane growth, which suggests that it could control cell size by measuring cell growth to determine when sufficient growth has occurred. Here, we show that signaling lipids play an important role in Pkc1 regulation. Pkc1 has a phosphatidylserine-binding domain and proportional phosphorylation of Pkc1 during membrane growth is dependent upon phosphatidylserine. Together, the data suggest that signals that measure and control plasma membrane growth are closely associated with the membrane itself.