Optical induction of Brn2 drives neural differentiation in embryonic stem cells
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The pluripotency network applies magnitude and duration thresholds to Brn2 inputs
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Nanog half-life determines minimum Brn2 input duration required to designate the input as “signal”
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Mathematical model predicts response of ESC to complex, time varying inputs
Summary
Stem cells occupy variable environments where they must distinguish stochastic fluctuations from developmental cues. Here, we use optogenetics to investigate how the pluripotency network in embryonic stem cells (ESCs) achieves a robust response to differentiation cues but not to gene expression fluctuations. We engineered mouse ESCs to allow quantitative control over the endogenous mechanism of neural differentiation through a light-inducible Brn2 transgene and monitored differentiation status through a genome-integrated Nanog-GFP reporter. By exposing cells to pulses of Brn2, we find that the pluripotency network rejects Brn2 inputs that are below specific magnitude or duration thresholds, but allows rapid differentiation when both thresholds are satisfied. The filtering properties of the network arise through its positive feedback architecture and the intrinsic half-life of Nanog, which determines the duration threshold in the network. Together our results suggest that the dynamic properties of positive feedback networks might determine how inputs are classified as signal or noise by stem cells.
