A set of monomeric near-infrared fluorescent proteins for multicolor imaging across scales

Bright monomeric near-infrared (NIR) fluorescent proteins (FPs) are in high demand as protein tags for multicolor microscopy and in vivo imaging. Here we apply rational design to engineer a complete set of monomeric NIR FPs, which are the brightest genetically encoded NIR probes. We demonstrate that the enhanced miRFP series of NIR FPs, which combine high effective brightness in mammalian cells and monomeric state, perform well in both nanometer-scale imaging with diffraction unlimited stimulated emission depletion (STED) microscopy and centimeter-scale imaging in mice. In STED we achieve -40nm resolution in live cells. In living mice we detect -10(5) fluorescent cells in deep tissues. Using spectrally distinct monomeric NIR FP variants, we perform two-color live-cell STED microscopy and two-color imaging in vivo. Having emission peaks from 670nm to 720nm, the next generation of miRFPs should become versatile NIR probes for multiplexed imaging across spatial scales in different modalities.Peer reviewe

A BK channel–mediated feedback pathway links single-synapse activity with action potential sharpening in repetitive firing

Action potential shape is a major determinant of synaptic transmission, and mechanisms of spike tuning are therefore of key functional significance. We demonstrate that synaptic activity itself modulates future spikes in the same neuron via a rapid feedback pathway. Using Ca2+ imaging and targeted uncaging approaches in layer 5 neocortical pyramidal neurons, we show that the single spike–evoked Ca2+ rise occurring in one proximal bouton or first node of Ranvier drives a significant sharpening of subsequent action potentials recorded at the soma. This form of intrinsic modulation, mediated by the activation of large-conductance Ca2+/voltage-dependent K+ channels (BK channels), acts to maintain high-frequency firing and limit runaway spike broadening during repetitive firing, preventing an otherwise significant escalation of synaptic transmission. Our findings identify a novel short-term presynaptic plasticity mechanism that uses the activity history of a bouton or adjacent axonal site to dynamically tune ongoing signaling properties

Red fluorescent genetically encoded indicator for intracellular hydrogen peroxide

Reactive oxygen species (ROS) are conserved regulators of numerous cellular functions, and overproduction of ROS is a hallmark of various pathological processes. Genetically encoded fluorescent probes are unique tools to study ROS production in living systems of different scale and complexity. However, the currently available recombinant redox sensors have green emission, which overlaps with the spectra of many other probes. Expanding the spectral range of recombinant in vivo ROS probes would enable multiparametric in vivo ROS detection. Here we present the first genetically encoded red fluorescent sensor for hydrogen peroxide detection, HyPerRed. The performance of this sensor is similar to its green analogues. We demonstrate the utility of the sensor by tracing low concentrations of H2O2 produced in the cytoplasm of cultured cells upon growth factor stimulation. Moreover, using HyPerRed we detect local and transient H2O2 production in the mitochondrial matrix upon inhibition of the endoplasmic reticulum Ca(2+) uptake

Detector Array Readout with Traveling Wave Amplifiers

Reducing noise to the quantum limit over a large bandwidth is a fundamental requirement for future applications operating at millikelvin temperatures, such as the neutrino mass measurement, the next-generation X-ray observatory, the CMB measurement, the dark matter and axion detection, and the rapid high-fidelity readout of superconducting qubits. The read out sensitivity of arrays of microcalorimeter detectors, resonant axion-detectors, and qubits, is currently limited by the noise temperature and bandwidth of the cryogenic amplifers. The Detector Array Readout with Traveling Wave Amplifers project has the goal of developing high-performing innovative traveling wave parametric amplifers with a high gain, a high saturation power, and a quantum-limited or nearly quantum-limited noise. The practical development follows two diferent promising approaches, one based on the Josephson junctions and the other one based on the kinetic inductance of a high-resistivity superconductor. In this contribution, we present the aims of the project, the adopted design solutions and preliminary results from simulations and measurements

Bimodal Approach for Noise Figures of Merit Evaluation in Quantum-Limited Josephson Traveling Wave Parametric Amplifiers

The advent of ultra-low noise microwave amplifiers revolutionized several research fields demanding quantum-limited technologies. Exploiting a theoretical bimodal description of a linear phase-preserving amplifier, in this contribution we analyze some of the intrinsic properties of a model architecture (i.e., an rf-SQUID based Josephson Traveling Wave Parametric Amplifier) in terms of amplification and noise generation for key case study input states (Fock and coherents). Furthermore, we present an analysis of the output signals generated by the parametric amplification mechanism when thermal noise fluctuations feed the device.Comment: 5 pages, 6 figure

A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized $^3$He from an Atomic Beam Source injected into the superfluid $^4$He and transported to the measurement cells as a co-magnetometer. The superfluid $^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level

Electric dipole moments and the search for new physics

Static electric dipole moments of nondegenerate systems probe mass scales for physics beyond the Standard Model well beyond those reached directly at high energy colliders. Discrimination between different physics models, however, requires complementary searches in atomic-molecular-and-optical, nuclear and particle physics. In this report, we discuss the current status and prospects in the near future for a compelling suite of such experiments, along with developments needed in the encompassing theoretical framework.Comment: Contribution to Snowmass 2021; updated with community edits and endorsement

How much H2O2 is produced by recombinant D-Amino acid oxidase in mammalian cells?

Yeast D-amino acid oxidase (DAO) can serve as a genetically encoded producer of reactive oxygen species (ROS) in redox signaling studies. However, dynamics of hydrogen peroxide production and its sensitivity to externally added D-alanine (D-Ala) in cells have not been determined. Here we show that DAO, fused to a genetically encoded H2O2 indicator HyPer, can be used for controlled production of ROS in living eukaryotic cells. We found a clear heterogeneity in ROS production dynamics between individual cells. Moreover, different cell lines demonstrated distinct sensitivity to added D-Ala. Finally, by comparing signals generated by the HyPer-DAO fusion protein versus coexpressed HyPer and DAO proteins, we show that the fusion system is more sensitive to hydrogen peroxide production. Our results show the utility of the HyPer-DAO genetically encoded system for redox signaling studies and suggest that H2O2 produced by DAO in the cytoplasm acts locally in close proximity to the enzyme

Visualization of intracellular hydrogen peroxide with HyPer, a genetically encoded fluorescent probe

The fluorescent sensor HyPer allows monitoring of intracellular H O levels with a high degree of sensitivity and specificity. Here, we provide a detailed protocol of ratiometric imaging of HO produced by cells during phagocytosis, including instructions for experiments on different commercial confocal systems, namely, Leica SP2, Leica SP5, and Carl Zeiss LSM, as well as wide-field Leica 6000 microscope. The general experimental scheme is easily adaptable for imaging HO production by various cell types under a variety of conditions