The mechanical properties of the extracellular environment govern key cellular decision-making processes such as proliferation, differentiation, or migration. [1] Thus, analyzing how cells gauge and interact with their mechanical environment is critical not only for understanding physiological and pathological processes but also for engineering cell and tissue growth and differentiation in regenerative medicine. [2] Although studies using passive elastic or viscoelastic materials have revealed valuable information about cell-matrix interactions, matrices with adjustable mechanical properties more closely reflect the dynamic environments many cells are exposed to in a living organism. [3] In order to recapitulate these dynamic environments, several materials have been developed, which enable the Interrogation and control of cellular fate and function using optogenetics is providing revolutionary insights into biology. Optogenetic control of cells is achieved by coupling genetically encoded photoreceptors to cellular effectors and enables unprecedented spatiotemporal control of signaling processes. Here, a fast and reversibly switchable photoreceptor is used to tune the mechanical properties of polymer materials in a fully reversible, wavelengthspecific, and dose-and space-controlled manner. By integrating engineered cyanobacterial phytochrome 1 into a poly(ethylene glycol) matrix, hydrogel materials responsive to light in the cell-compatible red/far-red spectrum are synthesized. These materials are applied to study in human mesenchymal stem cells how different mechanosignaling pathways respond to changing mechanical environments and to control the migration of primary immune cells in 3D. This optogenetics-inspired matrix allows fundamental questions of how cells react to dynamic mechanical environments to be addressed. Further, remote control of such matrices can create new opportunities for tissue engineering or provide a basis for optically stimulated drug depots. BiomaterialsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Caveolin-1 (Cav1) regulates the nanoscale organization and compartmentalization of the plasma membrane. Here we found that Cav1 controlled the distribution of nanoclusters of isotype-specific B cell antigen receptors (BCRs) on the surface of B cells. In mature B cells stimulated with antigen, the immunoglobulin M BCR (IgM-BCR) gained access to lipid domains enriched for GM1 glycolipids, by a process that was dependent on the phosphorylation of Cav1 by the Src family of kinases. Antigen-induced reorganization of nanoclusters of IgM-BCRs and IgD-BCRs regulated BCR signaling in vivo. In immature Cav1-deficient B cells, altered nanoscale organization of IgM-BCRs resulted in a failure of receptor editing and a skewed repertoire of B cells expressing immunoglobulin-μ heavy chains with hallmarks of poly- and auto-reactivity, which ultimately led to autoimmunity in mice. Thus, Cav1 emerges as a cell-intrinsic regulator that prevents B cell-induced autoimmunity by means of its role in plasma-membrane organization.

Optogenetic switches are emerging molecular tools for studying cellular processes as they offer higher spatiotemporal and quantitative precision than classical, chemical-based switches. Light-controllable gene expression systems designed to upregulate protein expression levels meanwhile show performances superior to their chemical-based counterparts. However, systems to reduce protein levels with similar efficiency are lagging behind. Here, we present a novel two-component, blue light-responsive optogenetic OFF switch (‘Blue-OFF’), which enables a rapid and quantitative down-regulation of a protein upon illumination. Blue-OFF combines the first light responsive repressor KRAB-EL222 with the protein degradation module B-LID (blue light-inducible degradation domain) to simultaneously control gene expression and protein stability with a single wavelength. Blue-OFF thus outperforms current optogenetic systems for controlling protein levels. The system is described by a mathematical model which aids in the choice of experimental conditions such as light intensity and illumination regime to obtain the desired outcome. This approach represents an advancement of dual-controlled optogenetic systems in which multiple photosensory modules operate synergistically. As exemplified here for the control of apoptosis in mammalian cell culture, the approach opens up novel perspectives in fundamental research and applications such as tissue engineering.

T lymphocytes expressing the γδ T cell receptor (γδ TCR) can recognize antigens expressed by tumor cells and subsequently kill these cells. γδ T cells are indeed used in cancer immunotherapy clinical trials. The anti-CD3ε antibody UCHT1 enhanced the in vitro tumor killing activity of human γδ T cells by an unknown molecular mechanism. Here, we demonstrate that Fab fragments of UCHT1, which only bind monovalently to the γδ TCR, also enhanced tumor killing by expanded human Vγ9Vδ2 γδ T cells or pan-γδ T cells of the peripheral blood. The Fab fragments induced Nck recruitment to the γδ TCR, suggesting that they stabilized the γδ TCR in an active CD3ε conformation. However, blocking the Nck-CD3ε interaction in γδ T cells using the small molecule inhibitor AX-024 neither reduced the γδ T cells’ natural nor the Fab-enhanced tumor killing activity. Likewise, Nck recruitment to CD3ε was not required for intracellular signaling, CD69 and CD25 up-regulation, or cytokine secretion by γδ T cells. Thus, the Nck-CD3ε interaction seems to be dispensable in γδ T cells.

In article number https://doi.org/10.1002/adma.201806727, Wilfried Weber and co‐workers present a synthetic extracellular matrix, the mechanical properties of which can be tuned in a fast and reversible manner by light in the red spectrum. They apply this matrix to optically control the migration of primary T lymphocytes and to analyze mechanosignalling in mesenchymal stem cells in response to dynamic mechanical cues. Cover image designed by Jo Richers (https://doi.org/www.jorichers.com).