Mechanical feedback coordinates cell wall expansion and assembly in yeast mating morphogenesis
Fig 2
Effect of mechanical feedback strength and turgor pressure on cell viability.
The strength of mechanical feedback, Γ, is experimentally varied by deleting MID2 and WSC1. The dimensionless parameter (PρwλX)/(12μ0mwρ0kp) is varied by changing the osmolarity of the external medium through dilution of the yeast growth media, YPD, in deionized H2O, effectively increasing turgor pressure P in cells. Cell lysis was measured using the PI staining viability assay (Methods). (A) Percent of lysed cells in the absence of α-factor for WT, mid2Δ and wsc1Δ mutants, as well as the mid2 Δwsc1Δ double mutant. (B) Percent of WT lysed cells when grown in the presence of α-factor in YPD medium with decreasing osmolarity. (C) Percent of mid2Δ wsc1Δ lysed cells when grown both in the presence and absence of α-factor in YPD, in osmotically supported conditions (YPD + 1M sorbitol), as well as in hypo-osmotic conditions (100% H2O). (D) Percent of mid2Δ wsc1Δ lysed cells when grown in the presence of α-factor and osmotically supported media (YPD + sorbitol), diluted for decreasing osmolarities. (E) Percent of lysed cells in mid2Δ and wsc1Δ mutants, as well as the mid2Δwsc1Δ double mutant, when grown in the presence of α-factor in YPD. (F) Theoretically predicted dynamical regimes for varying values of the mechanical feedback strength Γ and the ratio (PρwλX)/(12μ0mwρ0kp). Decreasing osmolarity experimentally, corresponds to increasing P and, therefore, moving along horizontal lines in the positive direction. Addition of zymolyase, a cell wall degrading enzyme, corresponds to decreasing the cell wall viscosity, moving also along horizontal lines in the positive direction. (G) Images (DIC, PI staining and merge) showing the moments before and after the piercing of the cell wall at the tip of a mating projection and subsequent cell lysis of a mid2Δ cell after the addition of zymolyase, for video see S1 Video. Scale bar, 2μm. (H) Temporal increase in the fraction of pierced mating projections for both mid2Δ (squares) and WT (circles) cells after addition of zymolyase.