Synthetic biological approaches to optogenetically control cell signaling
Graphical abstract
Introduction
Optogenetics provides the ability to gain light-control over genetically encoded cell components, and thereby ultimately over signaling pathways or biological processes. Contrary to chemically inducible systems, where spatiotemporal capabilities are limited by the diffusion and the half-life of inducing molecules, light provides an exquisite precision of control and thus opens unique possibilities to disentangle the principles that govern nature.
Originally, optogenetics has been implemented in neuroscience [1], where light-responsive ion channels serve for remote control of action potential and thereby neural networks. Over the years, the field has spread beyond this scope and nowadays also makes use of diverse light-responsive protein modules to mediate the control of various biological functions. This latter, synthetic biological aspect of optogenetics will be the theme of this short review. First, we briefly familiarize the reader with the commonly used light-responsive modules and then systematically present the currently available approaches for light-control of different cell parts, with a strong emphasis on the most recent advances. Afterwards, we concisely review the latest optogenetic applications both in cell culture and in vivo, outlining the trends and likely future perspectives of the field.
Section snippets
Toolbox of light-responsive switch modules
A vast spectrum of photoreceptor proteins and their light-dependent interaction partners can be found in nature. A few of them have been already adopted as light-inducible switch modules, which can be utilized as protein fusion domains to build light-controlled systems in both prokaryotic and eukaryotic hosts, including mammalian cell lines and animals. The switch modules function as reversible, light-inducible interaction partners, forming either heterodimers (UVR8/COP1, Cry2/CIB1, FKF1/GI,
Light-control of gene regulation
A broad range of optogenetic tools for light-controlled gene regulation in cells has been developed, targeting both the externally introduced and the endogenous genes. Typically, these tools are based on one of the following three design concepts: (i) an optogenetic two-hybrid system for light-controlled recruitment of a gene effector (most commonly a transcription factor), (ii) a light-controlled reconstitution of a split gene effector, or (iii) a light-controlled nuclear import of a gene
Optogenetics in cell biology
Altering signaling proteins by equipping them with light-sensing input modules allows us to systematically perturb and dissect intracellular signaling networks to reveal the mechanisms that underlie them and ultimately the cellular behavior.
Diverse protein receptors, including the members of different receptor tyrosine kinase (RTK) families [33, 34, 35] and an innate immune receptor DAI [36], as well as a plethora of downstream signaling components, such as GEFs [37, 38, 39•], small GTPases [27
Conclusions and future perspectives
Optogenetics has lately matured from mostly proof of concept tools and implementations to being an excellent means for answering biological questions that other research tools were not able to address. Specifically, optogenetic approaches provide a superb spatiotemporally resolved alternative to the chemically controlled systems and classic genetic manipulation techniques (e.g. knockout, mutation and overexpression).
While the current optogenetic applications in individual cells, addressing
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Acknowledgements
We would like to thank Matej Žnidarič for his help with the preparation of figures. This work was supported by the Excellence Initiative of the German Federal and State Governments (EXC-294-BIOSS).
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