Dev. Cell 36, 117–126 (2016)

Credit: ELSEVIER

Experimental control of protein localization will help decipher protein function and manipulate cell behaviors. The phytochrome optogenetic system exploits the red light–mediated heterodimerization of the phytochrome B protein (PHYB) with its partner phytochrome interaction factor (PIF) in the presence of the chromophore PCB. However, this technique has not yet been applied to multicellular organisms because of the inability of PCB to penetrate deep tissues and the poor expression of PHYB. Buckley et al. were able to successfully optimize this system for zebrafish embryos by delivering a newly purified version of PCB into the embryos along with a truncated version of PHYB that optimizes its expression. When a PHYB-CAAX construct is used to drive membrane localization, exposure to 650-nm light rapidly recruits PIF6 to the membrane. Shifting the light to 750 nm reverses membrane binding of PIF6. Subcellular control of localization can be achieved by focusing the 650-nm laser at a point of interest. Given their interest in the regulation of polarity during neurogenesis, the authors generated a Pard3-PIF6 fusion construct and were able to direct the apical polarity protein Pard3 and recruit its binding partner Pard6 to specific membrane locations in the neural progenitors by the spot of the 650-nm laser. Overall, the use of this modified phytochrome system offers the potential to regulate cellular behaviors with greater control in a multicellular organism.