A calcium- and light-gated switch to induce gene expression in activated neurons

Development of Cal-Light system Schematic drawing of Cal-Light system. M13 and calmodulin proteins are fused to c-terminus and n-terminus of TEV protease (TEV-C and TEV-N), respectively. When Ca2+ arises in the cytosol, M13 and calmodulin bind to each other and subsequently TEV-C and TEV-N regain proteolytic functions. However, TEV protease cannot recognize TEVseq easily in a dark condition, because TEVseq is inserted at the c-terminus of AsLOV2 J-helix. Blue light causes a conformational change of J-helix making TEVseq unmasked. Cleaved tTA translocates to the nucleus and initiates gene expression.

Despite recent advances in optogenetics, it remains challenging to manipulate gene expression in specific populations of neurons. We present a dual-protein switch system, Cal-Light, that translates neuronal-activity-mediated calcium signaling into gene expression in a light-dependent manner. In cultured neurons and brain slices, we show that Cal-Light drives expression of the reporter EGFP with high spatiotemporal resolution only in the presence of both blue light and calcium. Delivery of the Cal-Light components to the motor cortex of mice by viral vectors labels a subset of excitatory and inhibitory neurons related to learned lever-pressing behavior. By using Cal-Light to drive expression of the inhibitory receptor halorhodopsin (eNpHR), which responds to yellow light, we temporarily inhibit the lever-pressing behavior, confirming that the labeled neurons mediate the behavior. Thus, Cal-Light enables dissection of neural circuits underlying complex mammalian behaviors with high spatiotemporal precision.

Lee, D., Hyun, J.H., Jung, K., Hannan, P., and Kwon, H.-B. (2017). A calcium- and light-gated switch to induce gene expression in activated neurons. Nat Biotech advance online publication.