A transgenic zebrafish for direct optogenetic activation of FGF/ERK signaling

Dynamic FGF/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 the blue light-dimerizing LOV domain. Previously, this tool was introduced into zebrafish embryos by mRNA injection. Here, we develop a novel transgenic zebrafish ubiquitously expressing bOpto-FGF, Tg(ubi:bOpto-FGF), to streamline experimental workflows. We demonstrate robust blue light-mediated activation of FGF/ERK signaling in gastrulation-stage Tg(ubi:bOpto-FGF) homozygous and heterozygous embryos. Light-mediated signaling activation is more spatially uniform in transgenics compared to embryos injected with bOpto-FGF mRNA. Tg(ubi:bOpto-FGF) heterozygotes are light-responsive from late blastula stages through at least 24 hours post-fertilization. Finally, ectopic signaling in response to continuous light exposure starting at late blastula stage is activated within 3 minutes and maintained for at least 75 minutes. This transgenic line provides a powerful and convenient new strategy for experimental manipulation of FGF/ERK signaling dynamics in the vertebrate zebrafish model.