A transgenic zebrafish for spatiotemporal optogenetic activation of FGF/ERK signaling.

Dynamic fibroblast growth factor (FGF)/extracellular signal-regulated kinase (ERK) signaling plays key roles in development, regeneration, and disease. We recently developed a zebrafish-optimized optogenetic tool, bOpto-FGF, that enables reversible activation of FGF/ERK signaling in response to blue light (∼455 nm) by fusing a zebrafish receptor tyrosine kinase domain to a blue-light-dimerizing light oxygen voltage-sensing domain. Previously, this tool was introduced into zebrafish embryos by mRNA injection. Here, we develop Tg(ubi:bOpto-FGF), a novel transgenic zebrafish ubiquitously expressing bOpto-FGF, to streamline experimental workflows. We demonstrate robust blue-light-mediated activation of FGF/ERK signaling and FGF target gene expression in early gastrulation-stage Tg(ubi:bOpto-FGF) embryos. Light-mediated signaling activation at this stage is more spatially uniform in transgenics compared to mRNA-injected embryos, and ectopic signaling in response to continuous light exposure is activated within 3 min and maintained for at least 75 min. Furthermore, Tg(ubi:bOpto-FGF) heterozygotes are light responsive from late blastula stages through at least 24 h postfertilization. Finally, we demonstrate light-mediated spatially localized FGF/ERK signaling activation within 1 min in the head, trunk, and tail at 1 day postfertilization. This transgenic line provides a powerful and convenient new strategy for spatiotemporal manipulation of FGF/ERK signaling in the vertebrate zebrafish model.