With recent advances in fluorescence microscopy, resolution is often limited by the size of the label and the resulting linkage error, rather than the microscope itself. Site-specific incorporation of noncanonical amino acids (ncAAs) combined with bioorthogonal click chemistry provides a powerful tool for fluorescent protein labeling, overcoming the spatial uncertainty inherent to antibody-based probes. Here, we present a method to further improve labeling precision by combining ncAA labeling with expansion microscopy (ExM) for dual-color super-resolution imaging. After optimizing labeling procedures and fluorophore selection, we visualize and resolve the nanoscale distribution of Na,K-ATPase α1 and β1 subunits in expanded HEK 293T cells. We validate our approach by super-resolution STED imaging of the ncAA labeled β1 subunit in unexpanded cells. This work presents a strong framework for multiplexed, high-resolution imaging, suggesting that ncAA labeling combined with ExM enables biological imaging at the nanometer scale

DNA origami-based nanotechnology is a versatile tool for exploring fundamental biological questions and holds significant promise for future biomedical applications. Here, we leverage the optical transparency of the embryonic zebrafish to analyze live embryos injected intravenously with fluorescently labeled wireframe DNA origami nanosheets. Our approach integrated long-term, high-resolution imaging of transgenic live zebrafish embryos with single-cell RNA sequencing to elucidate the effects of oligolysine-polyethylene glycol copolymer (K-PEG) coating on the biodistribution of fluorescence signal in embryos injected with wireframe DNA origami nanosheets. We observed rapid accumulation of fluorescence signal in the caudal hematopoietic tissue (CHT). K-PEG coating mitigated the accumulation of fluorescence signal in CHT, enabling increased detection of signal in other tissues. Our findings highlighted the pivotal role of scavenger endothelial cells in DNA origami clearance, with K-PEG enabling the prolonged detection of fluorescence signal at the CHT. Furthermore, using a transgenic zebrafish line designed for targeted macrophage ablation, we found that macrophages contribute to the clearance of fluorescence signal in embryos injected with the noncoated but not with K-PEG-coated nanosheets. This study introduces a framework for the analyses of the biodistribution and clearance of DNA origami nanostructures in vivo with single-cell resolution in zebrafish models.

Despite widespread adoption of tissue clearing techniques in recent years, poor access to suitable light-sheet fluorescence microscopes remains a major obstacle for biomedical end-users. Here, we present descSPIM (desktop-equipped SPIM for cleared specimens), a low-cost ($20,000–50,000), low-expertise (one-day installation by a non-expert), yet practical do-it-yourself light-sheet microscope as a solution for this bottleneck. Even the most fundamental configuration of descSPIM enables multi-color imaging of whole mouse brains and a cancer cell line-derived xenograft tumor mass for the visualization of neurocircuitry, assessment of drug distribution, and pathological examination by false-colored hematoxylin and eosin staining in a three-dimensional manner. Academically open-sourced (https://github.com/dbsb-juntendo/descSPIM), descSPIM allows routine three-dimensional imaging of cleared samples in minutes. Thus, the dissemination of descSPIM will accelerate biomedical discoveries driven by tissue clearing technologies.

The sympathetic nervous system controls bodily functions including vascular tone, cardiac rhythm, and the “fight-or-flight response”. Sympathetic chain ganglia develop in parallel with preganglionic motor nerves extending from the neural tube, raising the question of whether axon targeting contributes to sympathetic chain formation. Using nerve-selective genetic ablations and lineage tracing in mouse, we reveal that motor nerve-associated Schwann cell precursors (SCPs) contribute sympathetic neurons and satellite glia after the initial seeding of sympathetic ganglia by neural crest. Motor nerve ablation causes mispositioning of SCP-derived sympathoblasts as well as sympathetic chain hypoplasia and fragmentation. Sympathetic neurons in motor-ablated embryos project precociously and abnormally towards dorsal root ganglia, eventually resulting in fusion of sympathetic and sensory ganglia. Cell interaction analysis identifies semaphorins as potential motor nerve-derived signaling molecules regulating sympathoblast positioning and outgrowth. Overall, central innervation functions both as infrastructure and regulatory niche to ensure the integrity of peripheral ganglia morphogenesis.

Speed is key during infectious disease outbreaks. It is essential, for example, to identify critical host binding factors to pathogens as fast as possible. The complexity of host plasma membrane is often a limiting factor hindering fast and accurate determination of host binding factors as well as high-throughput screening for neutralizing antimicrobial drug targets. Here, we describe a multiparametric and high-throughput platform tackling this bottleneck and enabling fast screens for host binding factors as well as new antiviral drug targets. The sensitivity and robustness of our platform were validated by blocking SARS-CoV-2 particles with nanobodies and IgGs from human serum samples.

The mechanisms that drive myocyte orientation and fusion to control muscle directionality are not well understood. Here authors show that the developing skeleton produces mechanical tension that instructs the directional outgrowth of skeletal muscles. Formation of oriented myofibrils is a key event in musculoskeletal development. However, the mechanisms that drive myocyte orientation and fusion to control muscle directionality in adults remain enigmatic. Here, we demonstrate that the developing skeleton instructs the directional outgrowth of skeletal muscle and other soft tissues during limb and facial morphogenesis in zebrafish and mouse. Time-lapse live imaging reveals that during early craniofacial development, myoblasts condense into round clusters corresponding to future muscle groups. These clusters undergo oriented stretch and alignment during embryonic growth. Genetic perturbation of cartilage patterning or size disrupts the directionality and number of myofibrils in vivo. Laser ablation of musculoskeletal attachment points reveals tension imposed by cartilage expansion on the forming myofibers. Application of continuous tension using artificial attachment points, or stretchable membrane substrates, is sufficient to drive polarization of myocyte populations in vitro. Overall, this work outlines a biomechanical guidance mechanism that is potentially useful for engineering functional skeletal muscle.

Delta-catenin (CTNND2) is an adhesive junction associated protein belonging to the family of p120 catenins. The human gene is located on the short arm of chromosome 5, the region deleted in Cri-du-chat syndrome (OMIM #123450). Heterozygous loss of CTNND2 has been linked to a wide spectrum of neurodevelopmental disorders such as autism, schizophrenia, and intellectual disability. Here we studied how heterozygous loss of ctnnd2b affects zebrafish embryonic development, and larvae and adult behavior. First, we observed a disorganization of neuronal subtypes in the developing forebrain, namely the presence of ectopic isl1-expressing cells and a local reduction of GABA-positive neurons in the optic recess region. Next, using time-lapse analysis, we found that the disorganized distribution of is1l-expressing forebrain neurons resulted from an increased specification of Isl1:GFP neurons. Finally, we studied the swimming patterns of both larval and adult heterozygous zebrafish and observed an increased activity compared to wildtype animals. Overall, this data suggests a role for ctnnd2b in the differentiation cascade of neuronal subtypes in specific regions of the vertebrate brain, with repercussions in the animal's behavior.

Cerebrospinal fluid-contacting (CSF-c) neurons line the central canal of the spinal cord and a subtype of CSF-c neurons expressing somatostatin, forms a homeostatic pH regulating system. Despite their importance, their intricate spatial organization is poorly understood. The function of another subtype of CSF-c neurons expressing dopamine is also investigated. Imaging methods with a high spatial resolution (5-10 nm) are used to resolve the synaptic and ciliary compartments of each individual cell in the spinal cord of the lamprey to elucidate their signalling pathways and to dissect the cellular organization. Here, light-sheet and expansion microscopy resolved the persistent ventral and lateral organization of dopamine- and somatostatin-expressing CSF-c neuronal subtypes. The density of somatostatin-containing dense-core vesicles, resolved by stimulated emission depletion microscopy, was shown to be markedly reduced upon each exposure to either alkaline or acidic pH and being part of a homeostatic response inhibiting movements. Their cilia symmetry was unravelled by stimulated emission depletion microscopy in expanded tissues as sensory with 9 + 0 microtubule duplets. The dopaminergic CSF-c neurons on the other hand have a motile cilium with the characteristic 9 + 2 duplets and are insensitive to pH changes. This novel experimental workflow elucidates the functional role of CSF-c neuron subtypes in situ paving the way for further spatial and functional cell-type classification.

Background: Although tissue clearing and subsequent whole-brain imaging is now possible, standard protocols need to be adjusted to the innate properties of each specific tissue for optimal results. This work modifies exiting protocols to clear fragile brain samples and documents a downstream pipeline for image processing and data analysis. New Method: We developed a clearing protocol, CUBIC-f, which we optimized for fragile samples, such as the salamander brain. We modified hydrophilic and aqueous’ tissue-clearing methods based on Advanced CUBIC by incorporating Omnipaque 350 for refractive index matching. Results: By combining CUBIC-f, light sheet microscopy and bioinformatic pipelines, we quantified neuronal cell density, traced genetically marked fluorescent cells over long distance, and performed high resolution characterization of neural progenitor cells in the salamander brain. We also found that CUBIC-f is suitable for conserving tissue integrity in embryonic mouse brains. Comparison with exiting methods: CUBIC-f shortens clearing and staining times, and requires less reagent use than Advanced CUBIC and Advanced CLARITY. Conclusion: CUBIC-f is suitable for conserving tissue integrity in embryonic mouse brains, larval and adult salamander brains which display considerable deformation using traditional CUBIC and CLARITY protocols.