Optogenetics and CRISPR: A New Relationship Built to Last.

Since the breakthrough discoveries that CRISPR-Cas9 nucleases can be easily programmed and employed to induce targeted double-strand breaks in mammalian cells, the gene editing field has grown exponentially. Today, CRISPR technologies based on engineered class II CRISPR effectors facilitate targeted modification of genes and RNA transcripts. Moreover, catalytically impaired CRISPR-Cas variants can be employed as programmable DNA binding domains and used to recruit effector proteins, such as transcriptional regulators, epigenetic modifiers or base-modifying enzymes, to selected genomic loci. The juxtaposition of CRISPR and optogenetics enables spatiotemporally confined and highly dynamic genome perturbations in living cells and animals and holds unprecedented potential for biology and biomedicine.Here, we provide an overview of the state-of-the-art methods for light-control of CRISPR effectors. We will detail the plethora of exciting applications enabled by these systems, including spatially confined genome editing, timed activation of endogenous genes, as well as remote control of chromatin-chromatin interactions. Finally, we will discuss limitations of current optogenetic CRISPR tools and point out routes for future innovation in this emerging field.