Curated Optogenetic Publication Database

Abstract: Regulated cell death plays a key role in immunity, development, and homeostasis, but is also associated with a number of pathologies such as autoinflammatory and neurodegenerative diseases and cancer. However, despite the extensive mechanistic research of different cell death modalities, the direct comparison of different forms of cell death and their consequences on the cellular and tissue level remain poorly characterized. Comparative studies are hindered by the mechanistic and kinetic differences between cell death modalities, as well as the inability to selectively induce different cell death programs in an individual cell within cell populations or tissues. In this method, we present a protocol for rapid and specific optogenetic activation of three major types of programmed cell death: apoptosis, necroptosis, and pyroptosis, using light-induced forced oligomerization of their major effector proteins (caspases or kinases).

Abstract: Gene deletion is one of the standard approaches in genetics to investigate the roles and functions of target genes. However, the influence of gene deletion on cellular phenotypes is usually analyzed sometime after the gene deletion was introduced. Such lags from gene deletion to phenotype evaluation could select only the fittest fraction of gene-deleted cells and hinder the detection of potentially diverse phenotypic consequences. Therefore, dynamic aspects of gene deletion, such as real-time propagation and compensation of deletion effects on cellular phenotypes, still need to be explored. To resolve this issue, we have recently introduced a new method that combines a photoactivatable Cre recombination system and microfluidic single-cell observation. This method enables us to induce gene deletion at desired timings in single bacterial cells and to monitor their dynamics for prolonged periods. Here, we detail the protocol for estimating the fractions of gene-deleted cells based on a batch-culture assay. The duration of blue light exposure significantly affects the fractions of gene-deleted cells. Therefore, gene-deleted and non-deleted cells can coexist in a cellular population by adjusting the duration of blue light exposure. Single-cell observations under such illumination conditions allow the comparison of temporal dynamics between gene-deleted and non-deleted cells and unravel phenotypic dynamics provoked by gene deletion.

Abstract: Secreted reporters have been demonstrated to be simple and useful tools for analyzing transcriptional regulation in mammalian cells. The distinctive feature of these assays is the ability to detect reporter gene expression in the culture supernatant without affecting the cell physiology or leading to cell lysis, which allows repeated experimentation and sampling of the culture medium using the same cell cultures. Secreted embryonic alkaline phosphatase (SEAP) is one of the most widely used reporter, which can be easily detected using colorimetry following incubation with a substrate, such as p-nitrophenol phosphate. In this report, we present detailed procedures for detection and quantification of the SEAP reporter. We believe that this step-by-step protocol can be easily used by researchers to monitor and measure molecular genetic events in a variety of mammalian cells due to its simplicity and ease of handling. Graphical abstract Schematic overview of the workflow described in this protocol.

Abstract: Alzheimer's Disease (AD) has long been associated with accumulation of extracellular amyloid plaques (Aβ) originating from the Amyloid Precursor Protein. Plaques have, however, been discovered in healthy individuals and not all AD brains show plaques, suggesting that extracellular Aβ aggregates may play a smaller role than anticipated. One limitation to studying Aβ peptide in vivo during disease progression is the inability to induce aggregation in a controlled manner. We developed an optogenetic method to induce Aβ aggregation and tested its biological influence in three model organisms-D. melanogaster, C. elegans and D. rerio. We generated a fluorescently labeled, optogenetic Aβ peptide that oligomerizes rapidly in vivo in the presence of blue light in all organisms. Here, we detail the procedures for expressing this fusion protein in animal models, investigating the effects on the nervous system using time lapse light-sheet microscopy, and performing metabolic assays to measure changes due to intracellular Aβ aggregation. This method, employing optogenetics to study the pathology of AD, allows spatial and temporal control in vivo that cannot be achieved by any other method at present.

Abstract: Modern microscopy methods are powerful tools for studying live cell signaling and biochemical reactions, enabling us to observe when and where these reactions take place from the level of a cell down to single molecules. With microscopy, each cell or molecule can be observed both before and after a given perturbation, facilitating better inference of cause and effect than is possible with destructive modes of signaling quantitation. As many inputs to cell signaling and biochemical systems originate as protein-protein interactions near the cell membrane, an outstanding challenge lies in controlling the timing, location and the magnitude of protein-protein interactions in these unique environments. Here, we detail our procedure for manipulating such spatial and temporal protein-protein interactions in a closed microscopy system using a LOVTRAP-based light-responsive protein-protein interaction system on a supported lipid bilayer. The system responds in seconds and can pattern details down to the one micron level. We used this technique to unlock fundamental aspects of T cell signaling, and this approach is generalizable to many other cell signaling and biochemical contexts.

Abstract: T cells are one major cell type of the immune system that use their T cell antigen receptor (TCR) to bind and respond to foreign molecules derived from pathogens. The ligand-TCR interaction half-lives determine stimulation outcome. Until recently, scientists relied on mutating either the TCR or its ligands to investigate how varying TCR-ligand interaction durations impacted on T cell activation. Our newly created opto-ligand-TCR system allowed us to precisely and reversibly control ligand binding to the TCR by light illumination. This system uses phytochrome B (PhyB) tetramers as a light-regulated TCR ligand. PhyB can be photoconverted between a binding (ON) and non-binding (OFF) conformation by 660 nm and 740 nm light illumination, respectively. PhyB ON is able to bind to a synthetic TCR, generated by fusing the PhyB interacting factor (PIF) to the TCRβ chain. Switching PhyB to the OFF conformation disrupts this interaction. Sufficiently long binding of PhyB tetramers to the PIF-TCR led to T cell activation as measured by calcium influx. Here, we describe protocols for how to generate the tetrameric ligand for our opto-ligand-TCR system, how to measure ligand-TCR binding by flow cytometry and how to quantify T cell activation via calcium influx.

Abstract: In the field of extracellular optogenetics, photoreceptors are applied outside of cells to obtain systems with a desired functionality. Among the diverse applied photoreceptors, phytochromes are the only ones that can be actively and reversibly switched between the active and inactive photostate by the illumination with cell-compatible red and far-red light. In this protocol, we describe the production of a biotinylated variant of the photosensory domain of A. thaliana phytochrome B (PhyB-AviTag) in E. coli with a single, optimized expression plasmid. We give detailed instructions for the purification of the protein by immobilized metal affinity chromatography and the characterization of the protein in terms of purity, biotinylation, spectral photoswitching and the light-dependent interaction with its interaction partner PIF6. In comparison to previous studies applying PhyB-AviTag, the optimized expression plasmid used in this protocol simplifies the production process and shows an increased yield and purity.