Optogenetics and photopharmacology enable the spatiotemporal control of cell and animal behavior by light. Red light offers deep tissue penetration and minimal phototoxicity, but very few red light-sensitive optogenetic methods are currently available. Here, we developed a red light-induced homodimerization domain. We first showed that an optimized sensory domain of the cyanobacterial phytochrome 1 (CPH1) can be expressed robustly and without cytotoxicity in human cells. We then applied this domain to induce dimerization of two receptor tyrosine kinases, the fibroblast growth factor receptor 1 and the neurotrophin receptor trkB. With this new optogenetic method in hand, we activated the MAPK/ERK pathway non-invasively in mammalian tissue and developed multi-color cell signaling experiments. The light-controlled dimerizer and the red light-activated receptor tyrosine kinases will prove useful to regulate a variety of cellular processes with light.

No abstract

Non-canonical Wnt signaling plays a central role for coordinated cell polarization and directed migration in metazoan development. While spatiotemporally restricted activation of non-canonical Wnt-signaling drives cell polarization in epithelial tissues, it remains unclear whether such instructive activity is also critical for directed mesenchymal cell migration. Here, we developed a light-activated version of the non-canonical Wnt receptor Frizzled 7 (Fz7) to analyze how restricted activation of non-canonical Wnt signaling affects directed anterior axial mesendoderm (prechordal plate, ppl) cell migration within the zebrafish gastrula. We found that Fz7 signaling is required for ppl cell protrusion formation and migration and that spatiotemporally restricted ectopic activation is capable of redirecting their migration. Finally, we show that uniform activation of Fz7 signaling in ppl cells fully rescues defective directed cell migration in fz7 mutant embryos. Together, our findings reveal that in contrast to the situation in epithelial cells, non-canonical Wnt signaling functions permissively rather than instructively in directed mesenchymal cell migration during gastrulation.

G-protein-coupled receptors (GPCRs) form the largest receptor family, relay environmental stimuli to changes in cell behavior and represent prime drug targets. Many GPCRs are classified as orphan receptors because of the limited knowledge on their ligands and coupling to cellular signaling machineries. Here, we engineer a library of 63 chimeric receptors that contain the signaling domains of human orphan and understudied GPCRs functionally linked to the light-sensing domain of rhodopsin. Upon stimulation with visible light, we identify activation of canonical cell signaling pathways, including cAMP-, Ca2+-, MAPK/ERK-, and Rho-dependent pathways, downstream of the engineered receptors. For the human pseudogene GPR33, we resurrect a signaling function that supports its hypothesized role as a pathogen entry site. These results demonstrate that substituting unknown chemical activators with a light switch can reveal information about protein function and provide an optically controlled protein library for exploring the physiology and therapeutic potential of understudied GPCRs.