Color vision extracts spectral information by comparing signals from photoreceptors with different visual pigments. Such comparisons are encoded by color-opponent neurons that are excited at one ...wavelength and inhibited at another. Here, we examine the circuit implementation of color-opponent processing in the Drosophila visual system by combining two-photon calcium imaging with genetic dissection of visual circuits. We report that color-opponent processing of UVshort/blue and UVlong/green is already implemented in R7/R8 inner photoreceptor terminals of “pale” and “yellow” ommatidia, respectively. R7 and R8 photoreceptors of the same type of ommatidia mutually inhibit each other directly via HisCl1 histamine receptors and receive additional feedback inhibition that requires the second histamine receptor Ort. Color-opponent processing at the first visual synapse represents an unexpected commonality between Drosophila and vertebrates; however, the differences in the molecular and cellular implementation suggest that the same principles evolved independently.
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•Physiological recordings reveal early stages of color opponency•R7 and R8 photoreceptors of the same type of ommatidia mutually inhibit each other•HisCl1 histamine receptor mediates direct inhibition between R7 and R8•Ort histamine receptor is required for feedback inhibition
The Drosophila visual system extracts different spectral information at the level of the first synapse, reminiscent of processing in the vertebrate retina.
Genetic calcium probes offer tremendous potential in the fields of neuroscience, cell biology, and pharmaceutical screening.
Previously, ratiometric and non-ratiometric indicators of cellular calcium ...dynamics have been described that consist of mutants
of the green fluorescent protein (GFP) as fluorophores and calmodulin as calcium-binding moiety in several configurations.
However, these calmodulin-based types of probes have a series of deficiencies, such as reduced dynamic ranges, when expressed
within transgenic organisms and lack of calcium sensitivity in certain targetings. We developed novel types of calcium probes
based on troponin C variants from skeletal and cardiac muscle. These indicators have ratio changes up to 140%, K d s ranging from 470 n m to 29 μ m , and improved subcellular targeting properties. We targeted the indicators to the plasma membrane of HEK293 cells and primary
hippocampal neurons. Upon long lasting depolarization, submembrane calcium levels in hippocampal neurons were found to be
in equilibrium with bulk cytosolic calcium levels, suggesting no standing gradient persists from the membrane toward the cytosol.
We expect that such novel indicators using specialized calcium sensing proteins will be minimally interacting with the cellular
biochemical machinery.
Protein engineering involves generating and screening large numbers of variants for desired properties. While modern DNA technology has made it easy to create protein diversity on the DNA level, the ...selection and validation of candidate proteins from large libraries remains a challenge. We built a screening platform that integrates high-quality fluorescence-based image analysis and robotic picking of bacterial colonies. It allows tracking each individual colony in a large population and collecting quantitative information on library composition during the protein evolution process. We demonstrate the power of the screening platform by optimizing a dim far-red-emitting fluorescent protein whose brightness increased several fold using iterative cycles of mutagenesis and platform-based screening. The resulting protein variant mCarmine is useful for imaging cells and structures within live tissue as well as for molecular tagging. Overall, the platform presented provides powerful, flexible, and low-cost instrumentation to accelerate many fluorescence-based protein optimization projects.
•Low-cost screening platform for image analysis and picking of bacterial colonies•Tracks each colony in a population expressing diversified protein libraries•Adaptable for many protein engineering projects•Platform was used to engineer mCarmine, a far-red-emitting fluorescent protein
Protein evolution requires generation and screening of large numbers of variants. To expedite screening, Fabritius et al. built a platform that integrates fluorescence-based image analysis and picking of bacterial colonies. They engineered mCarmine, a far-red-emitting fluorescent protein for tagging and deep tissue imaging.
An increasingly powerful set of new CRISPR/Cas-based methods is becoming available for directed evolution of proteins in mammalian cells. Although in vitro techniques or microbial expression systems ...have been dominating directed evolution, there are now promising approaches to diversify proteins in mammalian cells in situ. This can be achieved by simple indel mutagenesis or more sophisticated homology repair mechanisms for cassette mutagenesis of coding sequences. Cas9 variant fusions to base editors and other effectors pose another promising way to introduce diversity into proteins. CRISPR/Cas9-based directed evolution in mammalian cells opens a new exciting era of discovery for the many classes of proteins for which a mammalian cellular context is preferable.
Abstract
Calcium in interstitial fluids is central to systemic physiology and a crucial ion pool for entry into cells through numerous plasma membrane channels. Its study has been limited by the ...scarcity of methods that allow monitoring in tight inter-cell spaces of living tissues. Here we present high performance ultra-low affinity genetically encoded calcium biosensors named GreenT-ECs. GreenT-ECs combine large fluorescence changes upon calcium binding and binding affinities (Kds) ranging from 0.8 mM to 2.9 mM, making them tuned to calcium concentrations in extracellular organismal fluids. We validated GreenT-ECs in rodent hippocampal neurons and transgenic zebrafish in vivo, where the sensors enabled monitoring homeostatic regulation of tissue interstitial calcium. GreenT-ECs may become useful for recording very large calcium transients and for imaging calcium homeostasis in inter-cell structures in live tissues and organisms.
Endolysosomal organelles play a key role in trafficking, breakdown and receptor-mediated recycling of different macromolecules such as low-density lipoprotein (LDL)-cholesterol, epithelial growth ...factor (EGF) or transferrin. Here we examine the role of two-pore channel (TPC) 2, an endolysosomal cation channel, in these processes. Embryonic mouse fibroblasts and hepatocytes lacking TPC2 display a profound impairment of LDL-cholesterol and EGF/EGF-receptor trafficking. Mechanistically, both defects can be attributed to a dysfunction of the endolysosomal degradation pathway most likely on the level of late endosome to lysosome fusion. Importantly, endolysosomal acidification or lysosomal enzyme function are normal in TPC2-deficient cells. TPC2-deficient mice are highly susceptible to hepatic cholesterol overload and liver damage consistent with non-alcoholic fatty liver hepatitis. These findings indicate reduced metabolic reserve of hepatic cholesterol handling. Our results suggest that TPC2 plays a crucial role in trafficking in the endolysosomal degradation pathway and, thus, is potentially involved in the homoeostatic control of many macromolecules and cell metabolites.
Neuronal damage in autoimmune neuroinflammation is the correlate for long-term disability in multiple sclerosis (MS) patients. Here, we investigated the role of immune cells in neuronal damage ...processes in animal models of MS by monitoring experimental autoimmune encephalomyelitis (EAE) by using two-photon microscopy of living anaesthetized mice. In the brainstem, we detected sustained interaction between immune and neuronal cells, particularly during disease peak. Direct interaction of myelin oligodendrocyte glycoprotein (MOG)-specific Th17 and neuronal cells in demyelinating lesions was associated with extensive axonal damage. By combining confocal, electron, and intravital microscopy, we showed that these contacts remarkably resembled immune synapses or kinapses, albeit with the absence of potential T cell receptor engagement. Th17 cells induced severe, localized, and partially reversible fluctuation in neuronal intracellular Ca
2+ concentration as an early sign of neuronal damage. These results highlight the central role of the Th17 cell effector phenotype for neuronal dysfunction in chronic neuroinflammation.
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► Th17 cells establish immune-neuronal synapses and induce neuronal cell death in vitro ► Th17 cells directly contact neurons irrespective of their CNS-antigen specificity ► Th17 cell-neuronal interaction leads to severe neuronal dysfunction ► Th17 cell-mediated Ca
2+ elevation is partially reversible by blocking excitotoxicity
Mitochondrial redox signals have a central role in neuronal physiology and disease. Here we describe a new optical approach to measure fast redox signals with single-organelle resolution in living ...mice that express genetically encoded redox biosensors in their neuronal mitochondria. Moreover, we demonstrate how parallel measurements with several biosensors can integrate these redox signals into a comprehensive characterization of mitochondrial function. This approach revealed that axonal mitochondria undergo spontaneous 'contractions' that are accompanied by reversible redox changes. These contractions are amplified by neuronal activity and acute or chronic neuronal insults. Multiparametric imaging reveals that contractions constitute respiratory chain-dependent episodes of depolarization coinciding with matrix alkalinization, followed by uncoupling. In contrast, permanent mitochondrial damage after spinal cord injury depends on calcium influx and mitochondrial permeability transition. Thus, our approach allows us to identify heterogeneity among physiological and pathological redox signals, correlate such signals to functional and structural organelle dynamics and dissect the underlying mechanisms.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Transmembrane heparan sulfate proteoglycans regulate multiple aspects of cell behavior, but the molecular basis of their signaling is unresolved. The major family of transmembrane proteoglycans is ...the syndecans, present in virtually all nucleated cells, but with mostly unknown functions. Here, we show that syndecans regulate transient receptor potential canonical (TRPCs) channels to control cytosolic calcium equilibria and consequent cell behavior. In fibroblasts, ligand interactions with heparan sulfate of syndecan-4 recruit cytoplasmic protein kinase C to target serine714 of TRPC7 with subsequent control of the cytoskeleton and the myofibroblast phenotype. In epidermal keratinocytes a syndecan-TRPC4 complex controls adhesion, adherens junction composition, and early differentiation in vivo and in vitro. In Caenorhabditis elegans, the TRPC orthologues TRP-1 and -2 genetically complement the loss of syndecan by suppressing neuronal guidance and locomotory defects related to increases in neuronal calcium levels. The widespread and conserved syndecan-TRPC axis therefore fine tunes cytoskeletal organization and cell behavior.
Here, we describe a reporter system that consists of a FRET biosensor and its corresponding aptamer. The FRET biosensor employs the synthetic aptamer binding peptide Rsg1.2 sandwiched between mutants ...of the Green Fluorescent Protein and undergoes FRET when binding its corresponding Rev Responsive Element (RRE) RNA aptamer. We developed a novel approach to engineer FRET biosensors by linker extension and screening to improve signal strength of the biosensor which we called VAmPIRe (Viral Aptamer binding Peptide based Indicator for RNA detection). We demonstrate that the system is quantitative, reversible and works with high specificity in vitro and in vivo in living bacteria and mammalian cells. Thus, VAmPIRe may become valuable for RNA localizations and as a dynamic RNA-based reporter for live cell imaging. Moreover, functional screening of large libraries as demonstrated here may become applicable to optimize some of the many FRET biosensors of cellular signaling.
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