Single-component optogenetic control enables human portrait formation in cells

Continued exploration of novel photoreceptors is essential for advancing optogenetic tools, as differences in their reaction mechanisms and spectral sensitivity could enhance the versatility of available systems. While circadian clock photoreceptors represent promising candidates, only Arabidopsis Cryptochrome 2 (AtCRY2) has been widely adopted in current applications. Notably, both the light-dependent interaction of AtCRY2 with the CIB1 protein and its homodimerization have been exploited for diverse optogenetic applications. In our search for alternative circadian photoreceptors for optogenetic control, we aimed to develop a system functioning without the co-expression of interacting partners. In this context, Drosophila Cryptochrome (DmCRY) was a promising candidate due to its well-characterized photoreceptor function and defined light-dependent reaction mechanism. Upon illumination, DmCRY undergoes a conformational change that enables interactions with Jetlag and Timeless proteins, facilitating circadian clock resetting. DmCRY is also targeted for degradation via ubiquitylation by Jetlag and/or BRWD3, ensuring resetting occurs only once each morning. Notably, DmCRY is susceptible to light-induced degradation even when expressed in mammalian cells. Leveraging this property, we fused the Tet repressor (TetR) to the C-terminus of DmCRY to enable light-dependent regulation of gene expression via TetR-responsive elements. We demonstrate that this system modulates expression of Cas9 for gene knockout, dCas9 for transcriptional regulation, and recombinant proteins. Furthermore, using these tools with a photomasking technique, we generated human portrait images from cultured cells. These findings highlight DmCRY as a versatile optogenetic tool capable of controlling cellular processes with standard visible light, with potential for novel optogenetic platforms.