Recent advances in the development of genome editing technologies based on programmable nucleases have substantially improved our ability to make precise changes in the genomes of eukaryotic cells. Genome editing is already broadening our ability to elucidate the contribution of genetics to disease by facilitating the creation of more accurate cellular and animal models of pathological processes. A particularly tantalizing application of programmable nucleases is the potential to directly correct genetic mutations in affected tissues and cells to treat diseases that are refractory to traditional therapies. Here we discuss current progress toward developing programmable nuclease–based therapies as well as future prospects and challenges.

Here the customizable TALE DNA-binding domain was integrated with the light-sensitive cryptochrome 2 protein and its interacting partner (CIB1) from Arabidopsis thaliana, thereby creating an optogenetic two-hybrid system called light-inducible transcriptional effectors (LITEs); the LITE system establishes a novel mode of optogenetic control of endogenous transcription and epigenetic states. Feng Zhang and colleagues integrated the customizable TALE DNA-binding domain with the light-sensitive cryptochrome 2 protein and its interacting partner CIB1 from Arabidopsis thaliana, which they call LITEs (light-inducible transcriptional effectors), thereby creating an optogenetic two-hybrid system. LITEs do not require additional cofactors, are readily customized to target many loci and can be quickly and reversibly activated. They can also be packaged into viral vectors and targeted to specific cell populations. The authors applied this system in primary mouse neurons and in the brains of awake mice to modulate endogenous gene expression and to target epigenetic chromatin modifications. The LITE system establishes a novel mode of optogenetic control of endogenous cellular processes. The dynamic nature of gene expression enables cellular programming, homeostasis and environmental adaptation in living systems. Dissection of causal gene functions in cellular and organismal processes therefore necessitates approaches that enable spatially and temporally precise modulation of gene expression. Recently, a variety of microbial and plant-derived light-sensitive proteins have been engineered as optogenetic actuators, enabling high-precision spatiotemporal control of many cellular functions1,2,3,4,5,6,7,8,9,10,11. However, versatile and robust technologies that enable optical modulation of transcription in the mammalian endogenous genome remain elusive. Here we describe the development of light-inducible transcriptional effectors (LITEs), an optogenetic two-hybrid system integrating the customizable TALE DNA-binding domain12,13,14 with the light-sensitive cryptochrome 2 protein and its interacting partner CIB1 from Arabidopsis thaliana. LITEs do not require additional exogenous chemical cofactors, are easily customized to target many endogenous genomic loci, and can be activated within minutes with reversibility6,15. LITEs can be packaged into viral vectors and genetically targeted to probe specific cell populations. We have applied this system in primary mouse neurons, as well as in the brain of freely behaving mice in vivo to mediate reversible modulation of mammalian endogenous gene expression as well as targeted epigenetic chromatin modifications. The LITE system establishes a novel mode of optogenetic control of endogenous cellular processes and enables direct testing of the causal roles of genetic and epigenetic regulation in normal biological processes and disease states.

Significance: Understanding the design rules that govern the structure and function of natural biological systems gives us the ability to forward engineer machines integrated with and powered by biological components. Such machines, or “bio-bots,” can sense, process, and respond to dynamic environmental signals in real time, enabling a variety of applications. Here we present a modular optogenetic muscle actuator used to power actuation and locomotion of 3D printed flexible skeletons. Observing and controlling the functional response of such muscle-powered machines helps replicate the complex adaptive functionality we observe in natural biological systems. This demonstration thus sets the stage for building the next generation of bio-integrated machines and systems targeted at a diverse array of functional tasks.