Optogenetic Engineering: Light-Directed Cell Motility

Induction of Signal Transduction by Using Non-Channelrhodopsin-Type Optogenetic Tools

Signal transductions are the basis for all cellular functions. Previous studies investigating signal transductions mainly relied on pharmacological inhibition, RNA interference, and constitutive active/dominant negative protein expression systems. However, such studies do not allow the modulation of protein activity with high spatial and temporal precision in cells, tissues, and organs in animals. Recently, non-channelrhodopsin-type optogenetic tools for regulating signal transduction have emerged. These photoswitches address several disadvantages of previous techniques, and allow us to control a variety of signal transductions such as cell membrane dynamics, calcium signaling, lipid signaling, and apoptosis. In this review we summarize recent advances in the development of such photoswitches and in how these optotools are applied to signaling processes.

Phototriggered Secretion of Membrane Compartmentalized Bioactive Agents

A strategy for the light-activated release of bioactive compounds (BODIPY, colchicine, paclitaxel, and methotrexate) from membrane-enclosed depots is described. We have found that membrane-permeable bioagents can be rendered membrane impermeable by covalent attachment to cobalamin (Cbl) through a photocleavable linker. These Cbl-bioagent conjugates are imprisoned within lipid-enclosed compartments in the dark, as exemplified by their retention in the interior of erythrocytes. Subsequent illumination drives the secretion of the bioactive species from red blood cells. Photorelease is triggered by wavelengths in the red, far-red, and near-IR regions, which can be pre-assigned by affixing a fluorophore with the desired excitation wavelength to the Cbl-bioagent conjugate. Pre-assigned wavelengths allow different biologically active compounds to be specifically and unambiguously photoreleased from common carriers.

Optogenetic apoptosis: light-triggered cell death

An optogenetic Bax has been designed that facilitates light-induced apoptosis. We demonstrate that mitochondrial recruitment of a genetically encoded light-responsive Bax results in the release of mitochondrial proteins, downstream caspase-3 cleavage, changes in cellular morphology, and ultimately cell death. Mutagenesis of a key phosphorylatable residue or modification of the C-terminus mitigates background (dark) levels of apoptosis that result from Bax overexpression. The mechanism of optogenetic Bax-mediated apoptosis was explored using a series of small molecules known to interfere with various steps in programmed cell death. Optogenetic Bax appears to form a mitochondrial apoptosis-induced channel analogous to that of endogenous Bax.