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. Author manuscript; available in PMC: 2012 Mar 11.
Published in final edited form as: Nat Methods. 2011 Sep 11;8(10):837–839. doi: 10.1038/nmeth.1700

Figure 3. Feedback control can clamp PIP3 levels against cellular perturbations.

Figure 3

(a) The schematic depicts PI3K recruitment to a membrane target (Phy-mCherry-CAAX) using a fluorescent PIF fusion protein (iSH-YFP-PIF) that constitutively binds endogenous PI3K. 3′ PI lipid levels are assayed by PHAkt-Cerulean recruitment to the plasma membrane. (b) Feedback control can be used to clamp perturbations in upstream signaling nodes by adjusting light levels to compensate for these changes (such as LY294002 based PI3K inhibition or serum-based PI3K activation). (c,d) Upper panels: single-cell timecourses in response to a constant light input (dashed curve) or under feedback control (solid curve). At 400 s, 3′ PI lipid production is perturbed by addition of LY294002, a PI3K inhibitor (c) or serum, a PI3K activator (d). Lower panels: the time-varying light input used by the feedback controller to clamp 3′ PI lipid levels. AU: arbitrary units.