Abstract
Organelles are distributed to daughter cells, via inheritance pathways. However, it is unclear whether there are mechanisms beyond inheritance, which ensure that organelles are present in all cells. Here we present the unexpected finding that the yeast vacuole plays a positive essential role in initiation of the cell-cycle. When inheritance fails, a new vacuole is generated. We show that this occurs prior to the next cell-cycle, and gain insight into this alternative pathway. Moreover, we find that a combination of a defect in inheritance with an acute block in the vacuole biogenesis results in the loss of a functional vacuole and a specific arrest of cells in early G1 phase. Furthermore, this role for the vacuole in cell-cycle progression requires an intact TORC1-SCH9 pathway that can only signal from a mature vacuole. These mechanisms may serve as a checkpoint for the presence of the vacuole/lysosome.
Highlights
Organelles are essential for cellular functions, and organelle inheritance is likely a major pathway that ensures the presence of organelles in all cells
Jin and Weisman suggest that this newly identified communication between the vacuole and the nucleus may help to ensure that critical organelles are present in all cells. Though it remains unclear why the yeast vacuole is critical for a cell to divide, these findings suggest that the mammalian lysosome may perform a similar critical role in mammals
To test when and where a new vacuole is generated in the absence of vacuole inheritance, we monitored for the presence of a vacuole using two markers, Vph1 and FM4-64
Summary
Organelles are essential for cellular functions, and organelle inheritance is likely a major pathway that ensures the presence of organelles in all cells. Yeast generates vacuoles of a specific size prior to formation of a bud The new mother cells of vac17Δ, which lack FM4-64 (Figure 1A; open yellow arrowheads), had larger vacuoles compared to the newly formed vacuoles in the large buds. 63% of vac17Δ cells had GFP-Pep12 on the newly synthesized vacuole in the bud, which was Vph1-CFP positive but lacked FM4-64 (Figure 2F,G).
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