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. Author manuscript; available in PMC: 2022 Apr 1.
Published in final edited form as: Curr Opin Cell Biol. 2021 Feb 4;69:96–102. doi: 10.1016/j.ceb.2020.11.008

Figure 2. Positive feedback loops enable hysteresis and priming effects.

Figure 2.

(a) Topology of a general positive feedback loop. (b) Examples of positive feedback loops that generate cellular memories. Left: a diagram of the regulatory network underlying the adaptation to carbon source switch from glucose to maltose. Right: a diagram of the epigenetic regulatory network underlying H3K9me3-mediated gene silencing. (c) The time trace of a positive feedback system that induces an irreversible state transition in response to a transient stimulus. Inset: a bifurcation diagram that shows the steady state values as a function of the signal level, illustrating the origin of irreversibility. (d) The time trace of a positive feedback system that induces a reversible response upon a transient stimulus. Inset: a bifurcation diagram that shows the steady state values as a function of the signal level, illustrating the origin of the delay in recovery time.