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Robust spatial sensing of mating pheromone gradients by yeast cells.

Moore TI, Chou CS, Nie Q, Jeon NL, Yi TM - PLoS ONE (2008)

Bottom Line: We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone alpha-factor produced in a microfluidics chamber; the focus was on bar1Delta strains, which do not degrade the pheromone input.Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization.Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.

View Article: PubMed Central - PubMed

Affiliation: Department of Developmental and Cell Biology, University of California Irvine, Irvine, CA, USA.

ABSTRACT
Projecting or moving up a chemical gradient is a universal behavior of living organisms. We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone alpha-factor produced in a microfluidics chamber; the focus was on bar1Delta strains, which do not degrade the pheromone input. The yeast cells exhibited good accuracy with the mating projection typically pointing in the correct direction up the gradient ( approximately 80% under certain conditions), excellent sensitivity to shallow gradients, and broad dynamic range so that gradient-sensing was relatively robust over a 1000-fold range of average alpha-factor concentrations. Optimal directional sensing occurred at lower concentrations (5 nM) close to the K(d) of the receptor and with steeper gradient slopes. Pheromone supersensitive mutations (sst2Delta and ste2(300Delta)) that disrupt the down-regulation of heterotrimeric G-protein signaling caused defects in both sensing and response. Interestingly, yeast cells employed adaptive mechanisms to increase the robustness of the process including filamentous growth (i.e. directional distal budding) up the gradient at low pheromone concentrations, bending of the projection to be more aligned with the gradient, and forming a more accurate second projection when the first projection was in the wrong direction. Finally, the cells were able to amplify a shallow external gradient signal of alpha-factor to produce a dramatic polarization of signaling proteins at the front of the cell. Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization. Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.

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Pheromone gradient-sensing robustness strategies: schematic diagrams, data, and sample images.(A) At α-factor concentrations between 1 and 4 nM, many cells (bar1Δ) began to bud distally in a filamentous fashion. These filaments sensed the gradient as indicated by the direction of the bud relative to the mother cell and the resulting orientation was significantly (*** p<0.001; t-test) toward higher concentrations of mating factor. Scale bar = 50 µm. (B) At α-factor concentrations between 5 nM and 40 nM, cells made a wide mating projection that bent in the direction of the gradient. Determination of projection direction was aided by use of ConA-Alexa-488, which labeled the growing projection. Cells were imaged after 2, 4, and 6 hours of exposure. At each succeeding time interval the alignment with the gradient, cos(Θ), increased (* p<0.05; t-test). (C) At α-factor concentrations above 50 nM, if the initial projection was unaligned with the gradient, then instead of altering the projection to orient it toward the gradient, the cell abandoned its first attempt and formed a second projection after 6 hours, which was significantly (*** p<0.001; t-test) more aligned. Three independent experiments were performed (average±SEM).
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pone-0003865-g005: Pheromone gradient-sensing robustness strategies: schematic diagrams, data, and sample images.(A) At α-factor concentrations between 1 and 4 nM, many cells (bar1Δ) began to bud distally in a filamentous fashion. These filaments sensed the gradient as indicated by the direction of the bud relative to the mother cell and the resulting orientation was significantly (*** p<0.001; t-test) toward higher concentrations of mating factor. Scale bar = 50 µm. (B) At α-factor concentrations between 5 nM and 40 nM, cells made a wide mating projection that bent in the direction of the gradient. Determination of projection direction was aided by use of ConA-Alexa-488, which labeled the growing projection. Cells were imaged after 2, 4, and 6 hours of exposure. At each succeeding time interval the alignment with the gradient, cos(Θ), increased (* p<0.05; t-test). (C) At α-factor concentrations above 50 nM, if the initial projection was unaligned with the gradient, then instead of altering the projection to orient it toward the gradient, the cell abandoned its first attempt and formed a second projection after 6 hours, which was significantly (*** p<0.001; t-test) more aligned. Three independent experiments were performed (average±SEM).

Mentions: There were limitations to the response of cells to an α-factor gradient in terms of the directional accuracy of the initial projection, and whether a mating projection was created at all. At low concentrations of α-factor, most cells did not form a mating projection, and instead continued to divide. However, at approximately 2 nM, many cells did not bud axially to create cell clusters, but instead formed filaments that resulted from distal budding away from the birth site. Erdman and Snyder originally characterized this behavior [18]. We asked whether this pheromone-induced filamentous growth sensed and responded to the gradient. After one hour of α-factor exposure, the direction of new buds was random with respect to the gradient. Presumably, many of these buds were committed before the pheromone gradient was applied. After 3 hours, new buds did align with the gradient (cos(Θ)∼0.5) in a significant fashion. The same directionality was observed after 5 hours of gradient treatment when the next bud was made (Fig. 5A). Thus, pheromone-induced filamentous growth does sense and respond to the gradient.


Robust spatial sensing of mating pheromone gradients by yeast cells.

Moore TI, Chou CS, Nie Q, Jeon NL, Yi TM - PLoS ONE (2008)

Pheromone gradient-sensing robustness strategies: schematic diagrams, data, and sample images.(A) At α-factor concentrations between 1 and 4 nM, many cells (bar1Δ) began to bud distally in a filamentous fashion. These filaments sensed the gradient as indicated by the direction of the bud relative to the mother cell and the resulting orientation was significantly (*** p<0.001; t-test) toward higher concentrations of mating factor. Scale bar = 50 µm. (B) At α-factor concentrations between 5 nM and 40 nM, cells made a wide mating projection that bent in the direction of the gradient. Determination of projection direction was aided by use of ConA-Alexa-488, which labeled the growing projection. Cells were imaged after 2, 4, and 6 hours of exposure. At each succeeding time interval the alignment with the gradient, cos(Θ), increased (* p<0.05; t-test). (C) At α-factor concentrations above 50 nM, if the initial projection was unaligned with the gradient, then instead of altering the projection to orient it toward the gradient, the cell abandoned its first attempt and formed a second projection after 6 hours, which was significantly (*** p<0.001; t-test) more aligned. Three independent experiments were performed (average±SEM).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2586657&req=5

pone-0003865-g005: Pheromone gradient-sensing robustness strategies: schematic diagrams, data, and sample images.(A) At α-factor concentrations between 1 and 4 nM, many cells (bar1Δ) began to bud distally in a filamentous fashion. These filaments sensed the gradient as indicated by the direction of the bud relative to the mother cell and the resulting orientation was significantly (*** p<0.001; t-test) toward higher concentrations of mating factor. Scale bar = 50 µm. (B) At α-factor concentrations between 5 nM and 40 nM, cells made a wide mating projection that bent in the direction of the gradient. Determination of projection direction was aided by use of ConA-Alexa-488, which labeled the growing projection. Cells were imaged after 2, 4, and 6 hours of exposure. At each succeeding time interval the alignment with the gradient, cos(Θ), increased (* p<0.05; t-test). (C) At α-factor concentrations above 50 nM, if the initial projection was unaligned with the gradient, then instead of altering the projection to orient it toward the gradient, the cell abandoned its first attempt and formed a second projection after 6 hours, which was significantly (*** p<0.001; t-test) more aligned. Three independent experiments were performed (average±SEM).
Mentions: There were limitations to the response of cells to an α-factor gradient in terms of the directional accuracy of the initial projection, and whether a mating projection was created at all. At low concentrations of α-factor, most cells did not form a mating projection, and instead continued to divide. However, at approximately 2 nM, many cells did not bud axially to create cell clusters, but instead formed filaments that resulted from distal budding away from the birth site. Erdman and Snyder originally characterized this behavior [18]. We asked whether this pheromone-induced filamentous growth sensed and responded to the gradient. After one hour of α-factor exposure, the direction of new buds was random with respect to the gradient. Presumably, many of these buds were committed before the pheromone gradient was applied. After 3 hours, new buds did align with the gradient (cos(Θ)∼0.5) in a significant fashion. The same directionality was observed after 5 hours of gradient treatment when the next bud was made (Fig. 5A). Thus, pheromone-induced filamentous growth does sense and respond to the gradient.

Bottom Line: We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone alpha-factor produced in a microfluidics chamber; the focus was on bar1Delta strains, which do not degrade the pheromone input.Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization.Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.

View Article: PubMed Central - PubMed

Affiliation: Department of Developmental and Cell Biology, University of California Irvine, Irvine, CA, USA.

ABSTRACT
Projecting or moving up a chemical gradient is a universal behavior of living organisms. We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone alpha-factor produced in a microfluidics chamber; the focus was on bar1Delta strains, which do not degrade the pheromone input. The yeast cells exhibited good accuracy with the mating projection typically pointing in the correct direction up the gradient ( approximately 80% under certain conditions), excellent sensitivity to shallow gradients, and broad dynamic range so that gradient-sensing was relatively robust over a 1000-fold range of average alpha-factor concentrations. Optimal directional sensing occurred at lower concentrations (5 nM) close to the K(d) of the receptor and with steeper gradient slopes. Pheromone supersensitive mutations (sst2Delta and ste2(300Delta)) that disrupt the down-regulation of heterotrimeric G-protein signaling caused defects in both sensing and response. Interestingly, yeast cells employed adaptive mechanisms to increase the robustness of the process including filamentous growth (i.e. directional distal budding) up the gradient at low pheromone concentrations, bending of the projection to be more aligned with the gradient, and forming a more accurate second projection when the first projection was in the wrong direction. Finally, the cells were able to amplify a shallow external gradient signal of alpha-factor to produce a dramatic polarization of signaling proteins at the front of the cell. Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization. Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.

Show MeSH
Related in: MedlinePlus