FIG. 1.

Coupling the C120 regulatory element to the Fos basal promoter significantly increases light-induced expression. (A) Schematic comparing different C120-based reporter constructs, in which TAEL-responsive C120 sequences (C120) were coupled to either a minimal TATA box (TATA) or the basal promoter from the mouse Fos gene (Fos) and used to drive expression of mCherry. (B) Schematic of experimental design. Tg(C120T:mCherry) or Tg(C120F:mCherry) embryos were injected with TAEL mRNA. mCherry expression was induced by illuminating embryos with blue light starting at 3 hpf. (C) Comparison of light-induced mCherry expression in Tg(C120T:mCherry) and Tg(C120F:mCherry) embryos injected with TAEL mRNA. mCherry transcript levels were measured by qPCR from embryos illuminated with blue light for 1 h and compared to sibling embryos kept in the dark. Y-axis is set at log₂ scale. Dots represent biological replicates. Solid lines represent mean. Error bars represent SD. *p < 0.05. (D–G) Representative images of mCherry fluorescence in Tg(C120T:mCherry) (D, F) or Tg(C120F:mCherry) (E, G) embryos injected with TAEL mRNA and illuminated with blue light for 3 h (D, E) or kept in the dark (F, G). Images were acquired between 20 and 24 h postillumination. Scale bars, 200 μm. hpf, hours postfertilization; mRNA, messenger RNA; qPCR, quantitative polymerase chain reaction; SD, standard deviation.