Fig. 2

Transient light-activated gene expression in CHO cells. The LACE system was used to express eGFP in CHO cells in a light-activated manner. a DG44 cells were transfected with LACE plasmids. Mean fluorescence intensity (MFI) of eGFP signal was measured by flow cytometry with (blue) and without (black) 24 h of light activation with 465 nm light using 1 s pulses at 0.067 Hz pulse frequency and 9.8 mW/cm² intensity. eGFP only (negative control) represents the background fluorescence of cells (dashed line). b Tunability of eGFP expression was measured by altering LED intensity. MFI of eGFP signal from DG44 cells was measured by flow cytometry following 24 h of light activation at the indicated intensity. A fit of the data was performed assuming Michaelis-Menten kinetics. c Reversibility of eGFP expression was measured by monitoring eGFP MFI from DG44 and mRNA levels from CHO-K1 cells after turning off light activation. MFI and mRNA were measured by flow cytometry and qRT-PCR, respectively, at 0 and 24 h after light activation was terminated. d CHO-K1 cells were transfected with the indicated plasmids. Cells transfected with LACE plasmids were either exposed to light or kept in the dark. MFI of eGFP signal was measured at the indicated times. Data from (a) and (b) represent the mean values of five and three independent experiments, respectively. Data from (c) represent the mean values of three technical replicates in an experiment. Error bars represent standard error of the mean. Background fluorescence is indicated with a dashed line at the upper limit of the 95% confidence interval for negative control samples. P values were calculated with a paired two-tailed T-test