1. The Frequency Dependence of Osmo-Adaptation in Saccharomyces cerevisiae
Alexander van Oudenaarden Lab
Final Presentation
Mashaal Sohail
Emily Suter

2. Motivation
Cells respond to stimuli using complicated systems of biochemical reactions
Systems may comprise of hundreds of reactions
Interest in determining dominant processes that dictate system dynamics
Cells are constantly sensing and responding to their environments, and they do so through complex systems of biochemical reactions. Signaling cascades can consist of up to hundreds of different reactions. And each can occur over different time scales. Ligand-receptor interactions happen quickly, for example, whereas downstream gene expression is a much slower response. The motivation behind this group’s experiment was to determine which time scale, and therefore which reactions, dominates a particular response…

3. Hog1 MAPK Pathway
High-Osmolarity Glycerol (HOG) Mitogen-Activated Protein Kinase (MAPK) pathway in budding yeast Saccharomyces cerevisiae
Core pathway of the hyperosmotic shock response
To do this, they utilized the Hog1 MAPK pathway in budding yeast
This is the principle pathway of the hyperosmotic shock response in the cell. Hyperosmotic shock respose occurs when a cell experiences a rise in extracellular osmolarity, and then is forced to compensate lest it become dehydrated and shrivel.

4. Hog1 MAPK Pathway Hog1 cell nucleus
High-Osmolarity Glycerol (HOG) Mitogen-Activated Protein Kinase (MAPK) pathway in budding yeast Saccharomyces cerevisiae
Core pathway of the hyperosmotic shock response
Hog1
cell
nucleus

5. high osmolarity solution
Hog1 MAPK Pathway
High-Osmolarity Glycerol (HOG) Mitogen-Activated Protein Kinase (MAPK) pathway in budding yeast Saccharomyces cerevisiae
Core pathway of the hyperosmotic shock response
high osmolarity solution
Membrane proteins trigger a signal transduction cascade which culminates in the activation of Hog 1

6. Hog1 MAPK Pathway
High-Osmolarity Glycerol (HOG) Mitogen-Activated Protein Kinase (MAPK) pathway in budding yeast Saccharomyces cerevisiae
Core pathway of the hyperosmotic shock response
Then travels to the nucleus

7. Hog1 MAPK Pathway
High-Osmolarity Glycerol (HOG) Mitogen-Activated Protein Kinase (MAPK) pathway in budding yeast Saccharomyces cerevisiae
Core pathway of the hyperosmotic shock response
where it activates a broad transcription response to the osmotic stress.

8. Hog1 MAPK Pathway
High-Osmolarity Glycerol (HOG) Mitogen-Activated Protein Kinase (MAPK) pathway in budding yeast Saccharomyces cerevisiae
Core pathway of the hyperosmotic shock response
These proteins then help to increase the internal osmolarity and accommodate for the osmotic stress.

9. Experimental Setup

10. Experimental Setup

11. Experimental Setup

12. Experimental Setup

13. Fourier analysis approximates output signal as sin curve
Took this data and performed a fourier analysis and approximated the output as a sin curve. AsThe graph shows the red dots as in the previous slide

14. Linear time invariant model predicts system response to input signal
Hog1 Response to Single NaCl Step
by analyzing the frequency dependence of amplitude and phase shift, the authors were then able to develop a rpedictive model for the respose to osmotic signals. They created this predictive model by fitting linear time invariant model and used the parameters to predict the response to a one step input of 0.2 M NaCl. The red line is the model and those blue circles are the actually experimental data. It accurately predicted the response in tearms of both amplitude and time scale of response.

15. Pulsed-input analysis corresponds to biological network

16. Hog1-dependent feedback loop plays major role in rapid response
Hog1 Response to Single NaCl Step

17. Gene expression facilitates response to osmotic shocks on longer time scales
Wild Type
Inhibited Hog1 Expression
Response R(t)
time [min]

18. Significance/Conclusions
Showed that Hog1 MAPK pathway is governed by two different response time scales
Demonstrated use of frequency-response analysis on cellular networks
Utilized engineering principles to predict the response of dynamic stimuli

19. Significance/Conclusions
Showed that Hog1 MAPK pathway is governed by two different response time scales
Demonstrated use of frequency-response analysis on cellular networks
Utilized engineering principles to predict the response of dynamic stimuli
Thank you