Kinetic control of ERK2-GFP activation by light.

<p>(A) For light-induced ERK nuclear translocation, ERK2-GFP stayed within the nucleus as long as the blue light stimulation was maintained (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0092917#pone.0092917.s015" target="_blank">Movie S3</a>). No cytoplasmic retreatment of the nuclear ERK2-GFP was observed even after 60 min of light stimulation (yellow arrows). (B) On the other hand, EGF-induced ERK2-GFP nuclear localization was transient. Nuclear ERK2-GFP peaked around 10 min and decayed to pre-treatment level by 30 min (yellow arrow heads) despite the continuous presence of EGF (white arrows). (C) The normalized nuclear/cytoplasmic ERK2-GFP ratio, averaged over 10 cells, clearly showed distinctive kinetics of ERK activation under light and EGF stimulation. EGF stimulation induced a peak followed by a monotonic decay to the background, while light stimulation induced a sustained level as long as the light was on. (D) Reversible control of ERK activation by light. The same transfected cell was repeatedly subjected to light and dark cycles. For each light illumination period, ERK2-GFP translocated from the cytosol to the nucleus. After each dark period of 30 min, the ERK activity decreased to the base level. Snapshots of the cell at different time points were shown. Scale bar in A and B: 10 μm.