While traditional kinetic studies of the cytochrome b6f complex have frequently relied on measurements within the complex environment of intact leaves or whole-organism systems, such approaches can be limited by overlapping signals and physiological variables. This protocol advances existing frameworks by introducing a streamlined, multi-wavelength spectroscopic approach utilizing a reconstituted in vitro system to elucidate the inter-complex electron transfer kinetics between photosystem I and cytochrome b6f. Utilizing the JTS-150 pulsed spectrometer, supplied with a Smart Lamp, we monitored the redox transitions of P700+ and Cytf by simultaneously measuring the absorbance changes of our isolated complexes system in six different wavelengths (546, 554, 563, 574, 705, and 740 nm). Kinetic analysis was divided into two phases: laser-induced flash kinetics and steady-state actinic induction. We resolved the second-order re-reduction of P700+ by plastocyanin, accounting for detector saturation constraints with a 2 ms post-flash delay. Steady-state measurements under actinic light revealed complex Cytf turnover, characterized by a double-exponential decay. Furthermore, dark relaxation kinetics were used to quantify ferredoxin-mediated re-reduction of the cytochrome pool. By allowing the incorporation of specific regulatory and inhibitory factors, this methodology sets the ground for the deconvolution of competing electron pathways. It can therefore be used as a robust framework for assessing the mechanism of regulatory processes on photosynthetic flux. Key features • Activity measurement of isolated photosynthetic complexes. • Assessing interactions between complexes in the photosynthetic apparatus.

While cell hashing enhances single-cell RNA sequencing (scRNA-seq) efficiency and minimizes batch effects, commercial mouse hashtags often fail in FVB/N and several other strains due to antibody-epitope incompatibility. We describe a robust alternative utilizing biotinylated antibody cocktails and streptavidin-conjugated oligos to enable reliable sample multiplexing. This approach was validated in FVB/N lung tissues, yielding high-quality single-cell libraries. Our protocol offers a practical solution for researchers requiring strain-specific or custom-designed multiplexing strategies for single-cell transcriptomics. Key features • Strain-specific compatibility: Resolves the known H-2q haplotype mismatch in FVB/N mice that fails standard commercial MHC-I hashtag antibodies in cell hashing. • Multi-omic 5' workflow integration: Enables simultaneous sample multiplexing with 10× Genomics 5 chemistry, facilitating joint gene expression and V(D)J repertoire (TCR/BCR) profiling. • Enhanced non-immune cell labeling: Incorporates anti-CD326 (Ep-CAM) to ensure robust hashing of epithelial and tumor cells that may exhibit MHC-I downregulation or lack CD45. • Customizable biotin-streptavidin framework: Provides a modular system using biotinylated antibody cocktails and streptavidin-barcodes, adaptable for any mouse strain or tissue-specific cell markers.

Unsaturated fatty acids (UFAs) play key roles in essential cellular functions such as membrane dynamics, metabolism, and animal development. Disruptions in UFA metabolism are linked to metabolic, cardiovascular, and neurodegenerative disorders. Cellular UFAs composition and quantification are normally determined using methods such as gas chromatography and/or mass spectrometry, which require extraction procedures and prevent analysis of live specimens. Here, we describe a protocol that employs uniform 13C isotope labeling and high-resolution 2D solution-state nuclear magnetic resonance (NMR) spectroscopy to analyze lipid composition and fatty acid unsaturation directly in the model organism Caenorhabditis elegans. The approach enables in vivo assessment of lipid storage compositions with sufficient resolution and sensitivity to distinguish wild-type animals from those with altered fatty acid desaturation. Complementary analysis of total lipid extracts provides information regarding lipid molecules that are not detected in vivo, such as phospholipid molecules organized in biological membranes. Overall, this non-destructive NMR-based method offers a powerful tool for investigating lipid metabolism in C. elegans and other small model systems that can be isotopically enriched. Key features • Solution-state NMR spectroscopy is not destructive and can be used on live cells and multicellular organisms. • 13C isotopic enrichment is required for high-resolution NMR analysis of lipids in live C. elegans. • Lipid signals from live worms arise from the mobile lipid phase in lipid droplets. • NMR provides readouts of lipid compositions in live animals at a highly sensitive rate, enabling precise interpretation of the whole cell lipid metabolism.

The integrity of epithelial barriers is essential for maintaining tissue homeostasis, particularly in the intestinal tract, where it separates the host from the complex luminal environment. Two complementary, standard methods for assessing this barrier are transepithelial electrical resistance (TEER), which provides a rapid, non-destructive measure of ionic conductance across tight junctions, and the fluorescein isothiocyanate (FITC)-dextran assay, which directly quantifies paracellular macromolecule flux. This protocol details a robust and reproducible method for performing both assays using intestinal epithelial cell monolayers (e.g., Caco-2, T84) cultured on permeable Transwell supports. We outline the procedure from cell culture and monolayer differentiation to TEER measurement with an Epithelial Volt/Ohm Meter 3 (EVOM3) and the subsequent FITC-dextran permeability assay. By combining these techniques, this protocol provides a comprehensive assessment of barrier function, making it ideal for studying tight junction dynamics and regulation under various experimental conditions, such as cytokine stimulation, drug screening, or microbial challenges.Key features• Combines electrical resistance (TEER) and macromolecular flux (FITC-dextran) assays for a comprehensive assessment of intestinal epithelial barrier integrity.• Applicable to various intestinal models, including Caco-2 and T84 cell lines; can be applied to other immortalized or primary epithelial and endothelial cells.• Utilizes the Epithelial Volt/Ohm Meter 3 (EVOM3) for accurate, non-destructive, and rapid TEER measurements in intestinal epithelial cell monolayers.• Provides clear guidelines for EVOM3 electrode handling and measurement to ensure reproducible results.

The spatiotemporal dynamics and density of actin networks are key determinants of actin cytoskeleton-mediated cellular functions. In vitro reconstitution systems have been widely used to study actin cytoskeletal dynamics; however, many existing approaches offer limited flexibility in controlling the geometry, thickness, and density of the assembled actin networks. Here, we present an in vitro optogenetic protocol that enables precise control of actin network assembly on supported lipid bilayers using an improved light-induced dimer (iLID)-SspB-based light-inducible dimerization system. In this system, His-mEGFP-iLID is anchored to a Ni-NTA-containing lipid bilayer, while SspB-mScarlet-I-VCA, a nucleation-promoting factor fused with SspB, together with other actin cytoskeletal proteins, is supplied in bulk solution. Upon blue light illumination, SspB-mScarlet-I-VCA is recruited to the membrane in a spatially and temporally defined manner, inducing localized actin polymerization. By tuning illumination patterns and duration, actin networks with defined density, thickness, and geometry can be generated, and polymerization can be rapidly halted by stopping illumination. This protocol provides a versatile platform for reconstructing actin networks with controlled spatial organization and density, enabling quantitative analysis of density-dependent interactions between actin networks and actin-binding proteins. Key features • Actin networks with varying densities and arbitrary shapes can be formed on the same supported lipid bilayer by controlling blue light illumination through the objective lens. • Actin polymerization can be stopped simply by turning off blue light illumination, enabling the formation of actin networks with defined thicknesses. • This protocol requires purified actin and actin-binding proteins.

Natural killer (NK) cells are crucial innate immune effectors, mediating cytotoxicity against cancer and infected cells through receptors such as NKG2D. Reliable quantification of NK cell subsets is essential for evaluating NK cell-based immune responses in cancer research. Unlike other assays, including traditional flow cytometry used in assessing NK cells, imaging flow cytometry (IFC) is a simple and direct method for quantitative analysis of NK cells. This protocol describes the necessary procedures, including harvesting splenocytes, acquiring these cells labeled with NKG2D antibodies, and analyzing IFC data with IDEAS® software. We applied this protocol to quantitatively assess the number of splenic NKG2D+ NK cells in mice injected with SVTneg2 cancer cells (which carry the p53 G242A missense mutation) and compared them to mice injected with EMT6 cancer cells (which have wild-type p53) or normal fibroblasts. We found that the SVTneg2 cancer cells significantly decreased the number of NKG2D+ NK cells in mice by approximately 2-fold (933 cells vs. 2360 cells, p < 0.001) compared with mice injected with EMT6 cancer cells. This IFC protocol can be applied to directly quantify NK cells in vivo. This quantitative protocol allows novices to quickly handle the analysis of cytotoxic NK cells with a single NKG2D marker. Further multicolor flow cytometry and cytokine assay may be required to precisely define the subtypes and effects of NK cells in anticancer immunity. Key features • A simple and direct assay using imaging flow cytometry (IFC) to quantify cytotoxic NKG2D NK cells against breast cancer cells in mice. • Simultaneously collect the flow cytometry characters and each cell image of NK cells and other populations. • Step-by-step identification of interested NK cells mainly relying on image gating (focus, size, morphology). • Highly reliable and applicable to analyze other immune cell subsets or tumor-associated populations with corresponding conjugate antibodies.

Stochastic optical reconstruction microscopy (STORM) is a single-molecule localization microscopy technique that enables visualization of cellular structures beyond the diffraction limit. This approach has revealed previously inaccessible ultrastructural details in a wide range of cellular components, including the actin cytoskeleton, clathrin-coated pits, mitochondria, and bacterial nucleoid-associated proteins. STORM relies on the sequential emission of single photons from photosensitive fluorophores, which are precisely localized before entering a dark state or undergoing photobleaching. By activating fluorophores individually and fitting their point spread functions (PSFs), the center of mass can be calculated with a localization precision of up to ~20 nm. The parallel detection of thousands of single-molecule events, each assigned to distinct spatial coordinates, enables the reconstruction of a high-resolution image. Here, we describe a simple and efficient STORM workflow—including sample preparation, image acquisition, and quality control measurements—that we used to visualize various subcellular structures, such as mitochondria, microtubules, and lysosomes labeled with the commonly employed cyanine dye Alexa Fluor 647, as well as the actin cytoskeleton stained with Alexa Fluor 488–conjugated phalloidin. Image acquisition was performed using a conventional epifluorescence/total internal reflection (TIRF) microscope adapted for STORM imaging. Key adaptations included the use of a 160×/1.43 NA oil-immersion objective and a high-power mode, which concentrates the laser beam onto a small region of the sample, ensuring sufficient light intensity to drive fluorophores into the dark state. In addition, implementing a 1.6× magnification lens and a 4×4 binning camera mode allowed us to achieve a 100-nm pixel size optimal for reliable molecule detection. We believe that this protocol will be highly valuable to the microscopy community, as it lowers technical barriers to performing STORM on widely available microscopy platforms, thereby facilitating broader implementation of this powerful super-resolution technique.Key features• Optimized immunofluorescence, including multiple washing steps using 0.1% Tween-20 and a secondary antibody fixation step for single and dual-color STORM.• Imaging acquisition performed with a conventional epifluorescence/TIRF microscope adapted for STORM imaging.• Use of a 160×/1.43 NA oil-immersion objective and a high-power mode that concentrates the laser beam onto a small region of the sample.• Implementation of a 1.6× magnification lens and 4 × 4 camera binning to achieve 100 nm pixel size.

Super-resolution imaging of synapses in intact brain tissue remains challenging because light scattering, photobleaching, and limited probe penetration, along with antigen accessibility within the densely packed postsynaptic densities (PSDs), constrain resolution and labeling efficiency. Here, we present a protocol utilizing thin brain cryosections and tau-stimulated emission depletion (STED) nanoscopy to visualize the intricate nano-architecture of excitatory synapses in situ. Slicing the brain into 6 μm sections allows for highly efficient and even penetration of probes throughout sections while ensuring that the resolution is not significantly impacted by the imaging depth of the tissue. We outline step-by-step instructions for labeling pre- and postsynaptic nano-architecture using antibodies and nanobodies, highlighting how fixative choice influences the labeling efficiency of synaptic proteins. While this protocol is compatible with both confocal and super-resolution imaging, when combined with rapid image acquisition times of tau-STED, it enables clear separation of key synaptic features in three dimensions with minimal photobleaching. Thus, this approach enables robust multiplex imaging of fluorescently labeled synaptic proteins in the brain, providing exceptional spatial resolution for visualization and quantification of synaptic nanoarchitecture in its native environment. Key features • Detailed protocol for in situ 3D STED microscopy with ~50 nm XY and ~100 nm Z resolution. • Optimized strategies for labeling pre- and postsynaptic nano-architecture using antibodies and nanobodies, including guidance on fixative choice. • Unified workflow for visualizing synaptic morphology and nanoarchitecture to uncover molecular synaptic diversity in the brain at the nanoscale.

Breast cancer (BC) is the most frequently diagnosed malignancy in women and a leading cause of cancer-related mortality worldwide. Current clinical management relies on molecular classification—based on estrogen receptor (ER), progesterone receptor (PR), HER2, and Ki67 expression—to guide prognosis and therapy. Triple-negative breast cancer (TNBC), which lacks ER, PR, and HER2 expression, represents 15%–20% of cases and is characterized by aggressive behavior, early recurrence, and a paucity of targeted treatment options. These challenges underscore the urgent need for improved preclinical models that better recapitulate tumor biology to accelerate therapeutic discovery. While conventional monolayer (2D) cultures have contributed significantly to cancer research, they fail to mimic critical features of the three-dimensional (3D) tumor microenvironment (TME), thereby limiting clinical translation. To address this gap, 3D spheroid models have emerged as a powerful intermediary, more accurately replicating in vivo conditions such as cell–cell and cell–matrix interactions, nutrient and oxygen gradients, and the development of hypoxic cores. These features make spheroids a physiologically relevant platform for studying complex processes like metastasis, drug resistance, and treatment response. Here, we present a robust, simple, and cost-effective protocol for generating uniform 3D spheroids. Our method enables consistent monitoring of spheroid formation and growth over time, with quantitative, image-based size analysis to ensure reproducibility and scalability. Designed for flexibility, the protocol is broadly applicable across diverse cell types, effectively bridging the gap between traditional 2D cultures and complex in vivo studies. By providing an accessible and reliable model of the 3D TME, this protocol opens new avenues for high-throughput drug screening, mechanistic studies of tumor progression, and the advancement of personalized medicine strategies in breast cancer and beyond.Key features• Employs a cost-effective, lab-made agarose coating to create non-adherent surfaces in standard 96-well plates.• Optimized for reproducible spheroid formation from the aggressive MDA-MB-231 triple-negative breast cancer cell line.• Requires a brief orbital shaking step to promote homogeneous cell aggregation and formation of a single central spheroid per well.• Generates measurable spheroids within 96 h using only basic cell culture equipment and an orbital shaker.• Provides a clear workflow from spheroid formation to quantitative size analysis, using freely available (ImageJ) and widely used (GraphPad Prism) software.

ADGRL4 is an adhesion G protein-coupled receptor (aGPCR) implicated in tumour progression in multiple malignancies. We recently determined the first cryo-EM structure of active-state ADGRL4, revealing its weak coupling to the heterotrimeric G protein Gq and providing insights into its activation mechanism. Here, we describe a complete modular workflow for purifying active-state ADGRL4 over 2–3 days using a multifunctional tagging strategy incorporating multiple orthogonal detection, purification, and cleavage tags at the N-terminus as well as a tethered mini-Gq at the C-terminus. This configuration enhanced receptor cell-surface expression and stability and allowed different purification strategies to be tested during the development of the purification protocol. Although developed and optimised for ADGRL4, this approach is readily transferable to other weakly coupling aGPCRs or GPCRs where complex stability is a limiting factor for structural analysis.Key features• Complete workflow for purifying active-state ADGRL4 for cryo-EM analysis.• Modular, multifunctional N-terminal tagging strategy supporting multiple orthogonal purification and detection methods without any negative effect on cell surface expression levels.• Tethered mini-Gq increases stability and receptor cell-surface expression.• Modular purification tagging configuration provides freedom to change purification methodologies without having to perform additional receptor engineering or cloning.