Great paper just out in Mol Cell (which is publishing some great systems biology, ahem) by Aoki et al (http://www.sciencedirect.com/science/article/pii/S1097276513006850). They previously developed a FRET sensor for Erk activity, which has just an exceptional dynamic range; this is clearly a tool that works - as evidenced from the work of Albeck et al (also in mol cell). Aoki et al use a combination of drugs to examine how the MAPK signaling network is producing these spikes of activity as a result of a constant input signal. To control the dynamics on time scales associated with MAPK signaling optogenetics promises to be an important tool as photoswitching is fast and doesn't involved the stress of media change on mammalian cells that is associated with microfluidics. The one caveat to Aoki et al though is that I wasn't quite convinced that the cells experiencing pulses of activity induced by the optogenetic system would proliferate more quickly than the cells experiencing continuous activity, but that is a small caveat in what I think is an important step forward for quantitative signaling.
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