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Key events during the transition from rapid growth to quiescence in budding yeast require posttranscriptional regulators.

Li L, Miles S, Melville Z, Prasad A, Bradley G, Breeden LL - Mol. Biol. Cell (2013)

Bottom Line: These proteins deliver mRNAs to P-bodies, and at least one P-body component, Lsm1, also plays a unique role in Q-cell longevity.Cells lacking Lsm1 and Ssd1 or Mpt5 lose viability under these conditions and fail to enter the quiescent state.We conclude that posttranscriptional regulation of mRNAs plays a crucial role in the transition in and out of quiescence.

View Article: PubMed Central - PubMed

Affiliation: Basic Science Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109.

ABSTRACT
Yeast that naturally exhaust the glucose from their environment differentiate into three distinct cell types distinguishable by flow cytometry. Among these is a quiescent (Q) population, which is so named because of its uniform but readily reversed G1 arrest, its fortified cell walls, heat tolerance, and longevity. Daughter cells predominate in Q-cell populations and are the longest lived. The events that differentiate Q cells from nonquiescent (nonQ) cells are initiated within hours of the diauxic shift, when cells have scavenged all the glucose from the media. These include highly asymmetric cell divisions, which give rise to very small daughter cells. These daughters modify their cell walls by Sed1- and Ecm33-dependent and dithiothreitol-sensitive mechanisms that enhance Q-cell thermotolerance. Ssd1 speeds Q-cell wall assembly and enables mother cells to enter this state. Ssd1 and the related mRNA-binding protein Mpt5 play critical overlapping roles in Q-cell formation and longevity. These proteins deliver mRNAs to P-bodies, and at least one P-body component, Lsm1, also plays a unique role in Q-cell longevity. Cells lacking Lsm1 and Ssd1 or Mpt5 lose viability under these conditions and fail to enter the quiescent state. We conclude that posttranscriptional regulation of mRNAs plays a crucial role in the transition in and out of quiescence.

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Related in: MedlinePlus

Quiescent daughters outlive quiescent mothers. (A) W303 SSD1 and ssd1-d cells assayed for Q-cell yield at 1, 2, or 3 wk after inoculation into YEPD medium. (B) Thermotolerance of 1-wk-old Q cells as measured by colony-forming units (CFU) after 0–20 min at 55°C. (C) Trehalose and glycogen accumulation in stationary-phase cultures and Q cells. (D) SSD1 Q cells stained for bud scars (Calcofluor), dead cells (propidium iodide [PI]), and DIC after 10, 14, and 18 wk of suspension in water. (E) Q cells in D monitored for viability and (F) scored for live daughter and mother cells.
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Figure 5: Quiescent daughters outlive quiescent mothers. (A) W303 SSD1 and ssd1-d cells assayed for Q-cell yield at 1, 2, or 3 wk after inoculation into YEPD medium. (B) Thermotolerance of 1-wk-old Q cells as measured by colony-forming units (CFU) after 0–20 min at 55°C. (C) Trehalose and glycogen accumulation in stationary-phase cultures and Q cells. (D) SSD1 Q cells stained for bud scars (Calcofluor), dead cells (propidium iodide [PI]), and DIC after 10, 14, and 18 wk of suspension in water. (E) Q cells in D monitored for viability and (F) scored for live daughter and mother cells.

Mentions: We previously reported that prototrophic W303 carrying the SSD1 allele produces nearly twice as many Q cells as the isogenic strain carrying the truncated ssd1-d allele (Li et al., 2009). This is especially pronounced under long-term culture conditions (Figure 5A). Moreover, these purified Q cells survive in a nondividing state twice as long, and it is the ability to reenter the cell cycle, rather than cell viability, that is compromised by the loss of Ssd1 activity (Li et al., 2009). SSD1 Q cells are also more thermotolerant (Figure 5B), and upon refeeding, they recover and reenter the cell cycle more rapidly than W303 ssd1-d (see later discussion of Figure 7C). It has been suggested that differences in yield, longevity, thermotolerance, and recovery of Q cells could all be due to the high levels of glycogen and trehalose stored by these cells (Shi et al., 2010). However, SSD1 and ssd1-d stationary-phase cultures and purified Q cells accumulate equivalent levels of stored carbohydrate (Figure 5C). Clearly, the levels of these compounds cannot be solely responsible for the increased yield, thermotolerance, longevity, or recovery of SSD1 Q cells. Carbohydrate accumulation may be necessary, but it is not sufficient to confer these quiescent phenotypes.


Key events during the transition from rapid growth to quiescence in budding yeast require posttranscriptional regulators.

Li L, Miles S, Melville Z, Prasad A, Bradley G, Breeden LL - Mol. Biol. Cell (2013)

Quiescent daughters outlive quiescent mothers. (A) W303 SSD1 and ssd1-d cells assayed for Q-cell yield at 1, 2, or 3 wk after inoculation into YEPD medium. (B) Thermotolerance of 1-wk-old Q cells as measured by colony-forming units (CFU) after 0–20 min at 55°C. (C) Trehalose and glycogen accumulation in stationary-phase cultures and Q cells. (D) SSD1 Q cells stained for bud scars (Calcofluor), dead cells (propidium iodide [PI]), and DIC after 10, 14, and 18 wk of suspension in water. (E) Q cells in D monitored for viability and (F) scored for live daughter and mother cells.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 5: Quiescent daughters outlive quiescent mothers. (A) W303 SSD1 and ssd1-d cells assayed for Q-cell yield at 1, 2, or 3 wk after inoculation into YEPD medium. (B) Thermotolerance of 1-wk-old Q cells as measured by colony-forming units (CFU) after 0–20 min at 55°C. (C) Trehalose and glycogen accumulation in stationary-phase cultures and Q cells. (D) SSD1 Q cells stained for bud scars (Calcofluor), dead cells (propidium iodide [PI]), and DIC after 10, 14, and 18 wk of suspension in water. (E) Q cells in D monitored for viability and (F) scored for live daughter and mother cells.
Mentions: We previously reported that prototrophic W303 carrying the SSD1 allele produces nearly twice as many Q cells as the isogenic strain carrying the truncated ssd1-d allele (Li et al., 2009). This is especially pronounced under long-term culture conditions (Figure 5A). Moreover, these purified Q cells survive in a nondividing state twice as long, and it is the ability to reenter the cell cycle, rather than cell viability, that is compromised by the loss of Ssd1 activity (Li et al., 2009). SSD1 Q cells are also more thermotolerant (Figure 5B), and upon refeeding, they recover and reenter the cell cycle more rapidly than W303 ssd1-d (see later discussion of Figure 7C). It has been suggested that differences in yield, longevity, thermotolerance, and recovery of Q cells could all be due to the high levels of glycogen and trehalose stored by these cells (Shi et al., 2010). However, SSD1 and ssd1-d stationary-phase cultures and purified Q cells accumulate equivalent levels of stored carbohydrate (Figure 5C). Clearly, the levels of these compounds cannot be solely responsible for the increased yield, thermotolerance, longevity, or recovery of SSD1 Q cells. Carbohydrate accumulation may be necessary, but it is not sufficient to confer these quiescent phenotypes.

Bottom Line: These proteins deliver mRNAs to P-bodies, and at least one P-body component, Lsm1, also plays a unique role in Q-cell longevity.Cells lacking Lsm1 and Ssd1 or Mpt5 lose viability under these conditions and fail to enter the quiescent state.We conclude that posttranscriptional regulation of mRNAs plays a crucial role in the transition in and out of quiescence.

View Article: PubMed Central - PubMed

Affiliation: Basic Science Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109.

ABSTRACT
Yeast that naturally exhaust the glucose from their environment differentiate into three distinct cell types distinguishable by flow cytometry. Among these is a quiescent (Q) population, which is so named because of its uniform but readily reversed G1 arrest, its fortified cell walls, heat tolerance, and longevity. Daughter cells predominate in Q-cell populations and are the longest lived. The events that differentiate Q cells from nonquiescent (nonQ) cells are initiated within hours of the diauxic shift, when cells have scavenged all the glucose from the media. These include highly asymmetric cell divisions, which give rise to very small daughter cells. These daughters modify their cell walls by Sed1- and Ecm33-dependent and dithiothreitol-sensitive mechanisms that enhance Q-cell thermotolerance. Ssd1 speeds Q-cell wall assembly and enables mother cells to enter this state. Ssd1 and the related mRNA-binding protein Mpt5 play critical overlapping roles in Q-cell formation and longevity. These proteins deliver mRNAs to P-bodies, and at least one P-body component, Lsm1, also plays a unique role in Q-cell longevity. Cells lacking Lsm1 and Ssd1 or Mpt5 lose viability under these conditions and fail to enter the quiescent state. We conclude that posttranscriptional regulation of mRNAs plays a crucial role in the transition in and out of quiescence.

Show MeSH
Related in: MedlinePlus