Determining how cells generate and transduce mechanical forces at the nanoscale is a major technical challenge for the understanding of numerous physiological and pathological processes. Podosomes are submicrometer cell structures with a columnar F-actin core surrounded by a ring of adhesion proteins, which possess the singular ability to protrude into and probe the extracellular matrix. Using protrusion force microscopy, we have previously shown that single podosomes produce local nanoscale protrusions on the extracellular environment. However, how cellular forces are distributed to allow this protruding mechanism is still unknown. To investigate the molecular machinery of protrusion force generation, we performed mechanical simulations and developed quantitative image analyses of nanoscale architectural and mechanical measurements. First, in silico modeling showed that the deformations of the substrate made by podosomes require protrusion forces to be balanced by local traction forces at the immediate core periphery where the adhesion ring is located. Second, we showed that three-ring proteins are required for actin polymerization and protrusion force generation. Third, using DONALD, a 3D nanoscopy technique that provides 20 nm isotropic localization precision, we related force generation to the molecular extension of talin within the podosome ring, which requires vinculin and paxillin, indicating that the ring sustains mechanical tension. Our work demonstrates that the ring is a site of tension, balancing protrusion at the core. This local coupling of opposing forces forms the basis of protrusion and reveals the podosome as a nanoscale autonomous force generator.

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Daptomycin is a last-resort membrane-targeting lipopeptide approved for the treatment of drug-resistant staphylococcal infections, such as bacteremia and implant-related infections. Although cases of resistance to this antibiotic are rare, increasing numbers of clinical,in vitro, and animal studies report treatment failure, notably againstStaphylococcus aureus. The aim of this study was to identify the features of daptomycin and its target bacteria that lead to daptomycin treatment failure. We show that daptomycin bactericidal activity againstS. aureusvaries significantly with the growth state and strain, according to the membrane fatty acid composition. Daptomycin efficacy as an antibiotic relies on its ability to oligomerize within membranes and form pores that subsequently lead to cell death. Our findings ascertain that daptomycin interacts with tolerant bacteria and reaches its membrane target, regardless of its bactericidal activity. However, the final step of pore formation does not occur in cells that are daptomycin tolerant, strongly suggesting that it is incapable of oligomerization. Importantly, membrane fatty acid contents correlated with poor daptomycin bactericidal activity, which could be manipulated by fatty acid addition. In conclusion, daptomycin failure to treatS. aureusis not due to a lack of antibiotic-target interaction, but is driven by its capacity to form pores, which depends on membrane composition. Manipulation of membrane fluidity to restoreS. aureusdaptomycin bactericidal activityin vivocould open the way to novel antibiotic treatment strategies.

We propose a straightforward sample-based technique to calibrate the axial detection in 3D single molecule localization microscopy (SMLM). Using microspheres coated with fluorescent molecules, the calibration curves of PSF-shaping-or intensity-based measurements can be obtained for any required depth range from a few hundreds of nm to several tens of µm. This experimental method takes into account the effect of the spherical aberration without requiring computational correction.

Such radiation has a long-lived 4f-4f transition, observed when evaluating lanthanides resulting in sharp narrowband emission. This light emission can be supported even when incorporating the lanthanide ion in a dispersion medium that acts as a host matrix with diverse functionalities. [7,9] Two host matrix types for lanthanide ions are identified, namely, organic [10] and inorganic materials. [7,11] Inorganic materials have high lattice-binding energy combined with rigidness; thus, in most cases, they show greater chemical and thermal resistance and photostability against continuous excitation than organic materials. [1,8] Highly crystalline inorganic host matrices are typically preferred to reduce point defects emissions. Hence, attention should be given to the crystallinity of the host material and the nonradiative multiphonon relaxation caused by the crystal lattice. [9] In practice, low phonon energy hosts are preferred to utilize the luminescent activator effectively. [7] However, the commonly used SiO 2 (≈1100 cm −1 stretching vibration) presents low lanthanide solubility, [12,13] leading to cluster formation at high dopant contents (10 18 cm −3 ), [14] quenching the lanthanide emission. [13] In photonics, a substitute for SiO 2 is ZrO 2 , which has relatively good transparency in the visible and infrared range and low phonon energy (≈470 cm −1 ). [12] ZrO 2 occurs in three polymorphs, tetragonal, monoclinic, and cubic, denoted t-ZrO 2 , m-ZrO 2 , and Implementation of more refined structures at the nano to microscale is expected to advance applications in optics and photonics. This work presents the additive manufacturing of 3D luminescent microarchitectures emitting light in the visible range. A tailor-made organo-metallic resin suitable for two-photon lithography is developed, which upon thermal treatment in an oxygen-rich atmosphere allows the creation of silicon-free tetragonal (t-) and monoclinic (m-) ZrO 2 . The approach is unique because the tailor-made Zrresin is different from what is achieved in other reported approaches based on sol−gel resins. The Zr-resin is compatible with the Eu-rich dopant, a luminescent activator, which enables to tune the optical properties of the ZrO 2 structures upon annealing. The emission characteristics of the Eu-doped ZrO 2 microstructures are investigated in detail with cathodoluminescence and compared with the intrinsic optical properties of the ZrO 2 . The hosted Eu has an orange−red emission showcased using fluorescence microscopy. The presented structuring technology provides a new platform for the future development of 3D luminescent devices.

Here, we present a 3D localization-based super-resolution technique providing a slowly varying localization precision over a 1 μm range with precisions down to 15 nm. The axial localization is performed through a combination of point spread function (PSF) shaping and supercritical angle fluorescence (SAF), which yields absolute axial information. Using a dual-view scheme, the axial detection is decoupled from the lateral detection and optimized independently to provide a weakly anisotropic 3D resolution over the imaging range. This method can be readily implemented on most homemade PSF shaping setups and provides drift-free, tilt-insensitive and achromatic results. Its insensitivity to these unavoidable experimental biases is especially adapted for multicolor 3D super-resolution microscopy, as we demonstrate by imaging cell cytoskeleton, living bacteria membranes and axon periodic submembrane scaffolds. We further illustrate the interest of the technique for biological multicolor imaging over a several-μm range by direct merging of multiple acquisitions at different depths.

Focal adhesions (FAs) initiate chemical and mechanical signals involved in cell polarity, migration, proliferation and differentiation. Super-resolution microscopy revealed that FAs are organized at the nanoscale into functional layers from the lower plasma membrane to the upper actin cytoskeleton. Yet, how FAs proteins are guided into specific nano-layers to promote interaction with given targets is unknown. Using single protein tracking, super-resolution microscopy and functional assays, we link the molecular behavior and 3D nanoscale localization of kindlin with its function in integrin activation inside FAs. We show that immobilization of integrins in FAs depends on interaction with kindlin. Unlike talin, kindlin displays free diffusion along the plasma membrane outside and inside FAs. We demonstrate that the kindlin Pleckstrin Homology domain promotes membrane diffusion and localization to the membrane-proximal integrin nano-layer, necessary for kindlin enrichment and function in FAs. Using kindlin-deficient cells, we show that kindlin membrane localization and diffusion are crucial for integrin activation, cell spreading and FAs formation. Thus, kindlin uses a different route than talin to reach and activate integrins, providing a possible molecular basis for their complementarity during integrin activation.

We developed a 3D localization-based super-resolution technique providing an almost isotropic 3D resolution over a 1 µm range with precisions down to 15 nm. The axial localization is performed through a combination of point spread function (PSF) shaping and supercritical angle fluorescence (SAF), which yields absolute axial information. Using a dual-view scheme, the axial detection is decoupled from the lateral detection and optimized independently. This method can be readily implemented on most homemade PSF shaping setups and provides drift-free, tiltinsensitive and achromatic results. Its insensitivity to these unavoidable experimental biases is especially adapted for multicolor 3D super-resolution microscopy, as we demonstrate by imaging cell cytoskeleton, living bacteria membranes and axon periodic submembrane scaffolds. We further illustrate the interest of the technique for biological multicolor imaging over a several µm range by direct merging of multiple acquisitions at different depths.Despite recent advances in localization-based super-resolution techniques, 3D fluorescence imaging of biological samples remains a major challenge, mostly because of its lack of versatility. While photoactivated localization microscopy (PALM) and (direct) stochastic optical reconstruction microscopy ((d)STORM) can easily provide lateral a localization precision (i.e. the standard deviation of the position) down to 5-10 nm [1,2,3,4], a great deal of effort is being made to develop quantitative and reproducible 3D super-localization methods. The most widely used 3D SMLM technique is the astigmatic imaging, which relies on the use of a cylindrical lens to apply an astigmatic aberration in the detection path to encode the axial information in the shape of the spots, achieving an axial localization precision down to 20-25 nm [5]-though the precision varies with the axial position. Other Point Spread Function (PSF) shaping methods are also available [6,7,8], but their implementations are not as inexpensive and straightforward. Still, all PSF shaping methods including astigmatic imaging suffer from several drawbacks such as axial drifts, chromatic aberration, field-varying geometrical aberrations and sample tilts. These sources of biases often degrade the resolution or hinder 1 All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/385799 doi: bioRxiv preprint first posted online Aug. 6, 2018; colocalization and experiment reproducibility. Axial measurements can also be performed thanks to intensity-based techniques like Supercritical Angle Fluorescence (SAF) [9,10,11,12,13,14], which relies on the detection of the near-field emission of fluorophores coupled into propagative waves at the sample/glass coverslip interface due to the index mismatch. Combined with SMLM, this technique, called Direct Optical Nanoscopy with Axially Localized ...