Phase separation in the membranes creates domains rich in specific components. To date, the best example of micrometer-scale phase separation in an unperturbed live cell membrane occurs in yeast (yeast yeast) an organelle called a vacuole. Recent studies indicate that the stages are functionally important, allowing yeast to survive during periods of stress. We discovered that yeast regulates this phase transition; The temperature at which the membrane components mix in one phase is -15 °C above the growth temperature. To maintain this balance, yeast may adjust the level of ergosterol (a molecule structurally similar to cholesterol) in their membranes. Surprisingly, the depletion of sterols in the vacuole membranes leads to their phasic separation, contrary to previous assumptions.
Vacuole membranes, lysosomal organelles yeast yeast (The yeast is in budding), undergoes unusual changes during the normal growth cycle of the cell. The cycle begins with a phase of rapid cell growth. Then, when glucose becomes scarce, growth slows, and the vacuolar membranes separate to micrometer ranges of two liquid phases. Recent studies indicate that these domains promote yeast survival by regulating transmembrane proteins that play key roles in the central signaling pathway conserved among eukaryotes (TORC1). An outstanding question in the field has been whether and how cells regulate phase transitions in response to new physical conditions. Here, we measure transition temperatures and find that after an increase of about 15 °C, regular gap membranes appear, regardless of the growth temperature. Moreover, populations of cells growing at a single temperature regulate this transformation to occur over a surprisingly narrow temperature range. Remarkably, the transition temperature is linearly proportional to the growth temperature, which indicates that cells are physiologically adapted to maintain their proximity to the transition. Next, we ask how the yeast adjusts its membranes to achieve phase separation. We isolate vacuoles from yeast during the rapid phase of growth, when their membranes do not locally show spheres. Ergosterol is the main sterol in yeast. We find that domains appear when ergosterol is depleted, contrary to the prevailing assumption that increases in sterol concentration generally lead to membrane phase separation in vivo, but in agreement with previous studies using artificial and cell-derived membranes.
- accepted December 6, 2021.
Author contributions: CLL, CEC, AJM, and SLK designer research; CLL and CEC conducted research; CLL data analysis; CLL, AJM and SLK wrote the paper.
The book declares no competing interest.
This article is a direct PNAS submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2116007119/-/DCSupplemental.
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