The CreLite system. The light‐inducible protein binding pair, truncated phytochrome B (PhyBΔ) and the active protein binding domain of phytochrome B interacting factor 6 (PIF6APB) are fused with C‐terminus Cre (CreC) and N‐terminus Cre (CreN), respectively. A cofactor analog, phycocyanobilin (PCB), is required for PhyBΔ to be functional. Once exposed to red light (λ_max = 650 nm), the PhyBΔ and PIF6APB bind each other and bring the two halves of Cre together, resuming its recombinase activity

CreLite‐mediated recombination in zebrafish embryos. PhyBΔCreC and PIF6CreN gene were subcloned into pCS2+ expression vector for in vitro transcription, A. The resulting CreLite mRNAs, along with the cofactor phycocyanobilin (PCB), were microinjected into ubi:zebrabow zebrafish reporter line, B, which changes its color from red to either cyan and yellow depending on the Cre‐mediated recombination event. Injected embryos were exposed to 660 nm red light for an hour at shield stage, C. Negative controls including no PCB and no light exposure were examined, D. Embryos with both PCB and red light exposure show broad recombination in the animal. Fluorescence was analyzed in different tissues throughout the embryos, while signal from the yolk or yolk extension was excluded due to potential autofluorescence; scale bar = 1 mm. Yellow fluorescent protein (YFP) signal of converted animals shows color conversion in various tissues, E, including brain and otic vesicle (b), lens (l), muscle (m), and epithelial (epi) cells; scale bar = 100 μm

CreLite‐mediated recombination at different times in development. CreLite mRNAs injected ubi:zebrabow embryos were exposed to 660 nm red light in the LED lightbox, D, at different time points (ie, 6 hpf, 1 dpf), B,C. Embryos exposed at 6 hpf and 1 dpf were assessed at 2 dpf, while those exposed at 2 dpf were assessed at 3 dpf. Mean number of embryos containing cells that exhibit yellow fluorescent protein (YFP) and/or cyan fluorescent protein (CFP) fluorescence after red light exposure were counted, E. Data are from three independent experiments and error bars represent SD; ****P < .0001, **P < .01. Ordinary one‐way analysis of variance (ANOVA) with Dunnett's multiple comparisons test. n = total number of embryos in each group. Each data point represents a clutch of embryos. Data from the negative controls (NIC, phycocyanobilin [PCB], and −660 nm) was pooled from experiments from the different time points. NIC, noninjected control. Scale bar = 1 mm

Spatial and temporal recombination via CreLite. Regional locations of the developing eye were activated by exposure to red light at 1 dpf. CreLite mRNA and phycocyanobilin (PCB) injected ubi:zebrabow embryos were mounted rostrally, A, in LMP agarose. Regions of interest (red circle in B) were exposed to 640 nm laser (0 hpe). The color conversion was examined at 6 hpe, C; scale bar = 50 μm