A Versatile High-Vacuum Cryo-transfer System for Cryo-microscopy and Analytics

Cryogenic microscopy methods have gained increasing popularity, as they offer an unaltered view on the architecture of biological specimens. As a prerequisite, samples must be handled under cryogenic conditions below their recrystallization temperature, and contamination during sample transfer and handling must be prevented. We present a high-vacuum cryo-transfer system that streamlines the entire handling of frozen-hydrated samples from the vitrification process to low temperature imaging for scanning transmission electron microscopy and transmission electron microscopy. A template for cryo-electron microscopy and multimodal cryo-imaging approaches with numerous sample transfer steps is presented.

Automated analysis of filopodial length and spatially resolved protein concentration via adaptive shape tracking

A novel approach based on the convex-hull algorithm is used for parallel analysis of growth dynamics and relative spatiotemporal protein concentration along flexible filopodial protrusions. Testing of filopodia formation in silico, in vitro, and in vivo validates the robustness and sensitivity of the proposed approach.

Filopodia are dynamic, actin-rich structures that transiently form on a variety of cell types. To understand the underlying control mechanisms requires precise monitoring of localization and concentration of individual regulatory and structural proteins as filopodia elongate and subsequently retract. Although several methods exist that analyze changes in filopodial shape, a software solution to reliably correlate growth dynamics with spatially resolved protein concentration along the filopodium independent of bending, lateral shift, or tilting is missing. Here we introduce a novel approach based on the convex-hull algorithm for parallel analysis of growth dynamics and relative spatiotemporal protein concentration along flexible filopodial protrusions. Detailed in silico tests using various geometries confirm that our technique accurately tracks growth dynamics and relative protein concentration along the filopodial length for a broad range of signal distributions. To validate our technique in living cells, we measure filopodial dynamics and quantify spatiotemporal localization of filopodia-associated proteins during the filopodial extension–retraction cycle in a variety of cell types in vitro and in vivo. Together these results show that the technique is suitable for simultaneous analysis of growth dynamics and spatiotemporal protein enrichment along filopodia. To allow readily application by other laboratories, we share source code and instructions for software handling.

C3G/Rapgef1 Is Required in Multipolar Neurons for the Transition to a Bipolar Morphology during Cortical Development

The establishment of a polarized morphology is essential for the development and function of neurons. During the development of the mammalian neocortex, neurons arise in the ventricular zone (VZ) from radial glia cells (RGCs) and leave the VZ to generate the cortical plate (CP). During their migration, newborn neurons first assume a multipolar morphology in the subventricular zone (SVZ) and lower intermediate zone (IZ). Subsequently, they undergo a multi-to-bipolar (MTB) transition to become bipolar in the upper IZ by developing a leading process and a trailing axon. The small GTPases Rap1A and Rap1B act as master regulators of neural cell polarity in the developing mouse neocortex. They are required for maintaining the polarity of RGCs and directing the MTB transition of multipolar neurons. Here we show that the Rap1 guanine nucleotide exchange factor (GEF) C3G (encoded by the Rapgef1 gene) is a crucial regulator of the MTB transition in vivo by conditionally inactivating the Rapgef1 gene in the developing mouse cortex at different time points during neuronal development. Inactivation of C3G results in defects in neuronal migration, axon formation and cortical lamination. Live cell imaging shows that C3G is required in cortical neurons for both the specification of an axon and the initiation of radial migration by forming a leading process.

Facile synthesis of a peptidic Au(I)-metalloamphiphile and its self-assembly into luminescent micelles in water

We report a short synthetic route for the preparation of a peptidic Au(I)-metalloamphiphile which, in buffered environments of physiological ionic strength, self-assembles into luminescent micellar nanostructures of 14 nm in diameter.

Spatiotemporally Controlled Reorganization of Signaling Complexes in the Plasma Membrane of Living Cells

Triggered immobilization of proteins in the plasma membrane of living cells into functional micropatterns is established by using an adaptor protein, which is comprised of an antiGFP nanobody fused to the HaloTag protein. Efficient in situ reorganization of the type I interferon receptor subunits as well as intact, fully functional signaling complexes in living cells are achieved by this method.

Tuning the pH-triggered self-assembly of dendritic peptide amphiphiles using fluorinated side chains

We report the synthesis of a series of anionic dendritic peptide amphiphiles of increasing hydrophobic character and describe their self-assembly into supramolecular nanorods using pH and ionic strength dependent state diagrams.

Blocking endocytosis enhances short-term synaptic depression under conditions of normal availability of vesicles

It is commonly thought that clathrin-mediated endocytosis is the rate-limiting step of synaptic transmission in small CNS boutons with limited capacity for synaptic vesicles, causing short-term depression during high rates of synaptic transmission. Here, we show by analyzing synaptopHluorin fluorescence that 200 action potentials evoke the same cumulative amount of vesicle fusion, irrespective of the frequency of stimulation (5-40 Hz), implying the absence of vesicle reuse, since the method used (alkaline-trapping) measures only first-round exocytosis. After blocking all slow or specifically clathrin-mediated endocytosis, however, the same stimulation patterns cause a rapid stimulation-frequency-dependent release depression. This form of depression does not reflect insufficient vesicle supply, but appears to be the result of slow clearance of vesicular components from the release site. Our findings uncover an important yet overlooked role of endocytic proteins for release site clearance in addition to their well-characterized role in endocytosis itself.

Genetic correction of a LRRK2 mutation in human iPSCs links parkinsonian neurodegeneration to ERK-dependent changes in gene expression

The LRRK2 mutation G2019S is the most common genetic cause of Parkinson's disease (PD). To better understand the link between mutant LRRK2 and PD pathology, we derived induced pluripotent stem cells from PD patients harboring LRRK2 G2019S and then specifically corrected the mutant LRRK2 allele. We demonstrate that gene correction resulted in phenotypic rescue in differentiated neurons and uncovered expression changes associated with LRRK2 G2019S. We found that LRRK2 G2019S induced dysregulation of CPNE8, MAP7, UHRF2, ANXA1, and CADPS2. Knockdown experiments demonstrated that four of these genes contribute to dopaminergic neurodegeneration. LRRK2 G2019S induced increased extracellular-signal-regulated kinase 1/2 (ERK) phosphorylation. Transcriptional dysregulation of CADPS2, CPNE8, and UHRF2 was dependent on ERK activity. We show that multiple PD-associated phenotypes were ameliorated by inhibition of ERK. Therefore, our results provide mechanistic insight into the pathogenesis induced by mutant LRRK2 and pointers for the development of potential new therapeutics.

Imaging the invisible: resolving cellular microcompartments by superresolution microscopy techniques

Unraveling the spatio-temporal organization of dynamic cellular microcompartments requires live cell imaging techniques capable of resolving submicroscopic structures. While the resolution of traditional far-field fluorescence imaging techniques is limited by the diffraction barrier, several fluorescence-based microscopy techniques providing sub-100 nm resolution have become available during the past decade. Here, we briefly introduce the optical principles of these techniques and compare their capabilities and limitations with respect to spatial and temporal resolution as well as live cell capabilities. Moreover, we summarize how these techniques contributed to a better understanding of plasma membrane microdomains, the dynamic nanoscale organization of neuronal synapses and the sub-compartmentation of microorganisms. Based on these applications, we highlight complementarity of these techniques and their potential to address specific challenges in the context of dynamic cellular microcompartments, as well as the perspectives to overcome current limitations of these methods.

Bacteria tracking by in vivo magnetic resonance imaging

Background

Different non-invasive real-time imaging techniques have been developed over the last decades to study bacterial pathogenic mechanisms in mouse models by following infections over a time course. In vivo investigations of bacterial infections previously relied mostly on bioluminescence imaging (BLI), which is able to localize metabolically active bacteria, but provides no data on the status of the involved organs in the infected host organism. In this study we established an in vivo imaging platform by magnetic resonance imaging (MRI) for tracking bacteria in mouse models of infection to study infection biology of clinically relevant bacteria.

Results

We have developed a method to label Gram-positive and Gram-negative bacteria with iron oxide nano particles and detected and pursued these with MRI. The key step for successful labeling was to manipulate the bacterial surface charge by producing electro-competent cells enabling charge interactions between the iron particles and the cell wall. Different particle sizes and coatings were tested for their ability to attach to the cell wall and possible labeling mechanisms were elaborated by comparing Gram-positive and -negative bacterial characteristics. With 5-nm citrate-coated particles an iron load of 0.015 ± 0.002 pg Fe/bacterial cell was achieved for Staphylococcus aureus. In both a subcutaneous and a systemic infection model induced by iron-labeled S. aureus bacteria, high resolution MR images allowed for bacterial tracking and provided information on the morphology of organs and the inflammatory response.

Conclusion

Labeled with iron oxide particles, in vivo detection of small S. aureus colonies in infection models is feasible by MRI and provides a versatile tool to follow bacterial infections in vivo. The established cell labeling strategy can easily be transferred to other bacterial species and thus provides a conceptual advance in the field of molecular MRI.

Internalization pathways of anisotropic disc-shaped zeolite L nanocrystals with different surface properties in HeLa cancer cells

Information about the mechanisms underlying the interactions of nanoparticles with living cells is crucial for their medical application and also provides indications of the putative toxicity of such materials. Here the uptake and intracellular delivery of disc-shaped zeolite L nanocrystals as porous aminosilicates with well-defined crystal structure, uncoated as well as with COOH-, NH2 -, polyethyleneglycol (PEG)- and polyallylamine hydrochloride (PAH) surface coatings are reported. HeLa cells are used as a model system to demonstrate the relation between these particles and cancer cells. Interactions are studied in terms of their fates under diverse in vitro cell culture conditions. Differently charged coatings demonstrated dissimilar behavior in terms of agglomeration in media, serum protein adsorption, nanoparticle cytotoxicity and cell internalization. It is also found that functionalized disc-shaped zeolite L particles enter the cancer cells via different, partly not yet characterized, pathways. These in vitro results provide additional insight about low-aspect ratio anisotropic nanoparticle interactions with cancer cells and demonstrate the possibility to manipulate the interactions of nanoparticles and cells by surface coating for the use of nanoparticles in medical applications.

Derivation and expansion using only small molecules of human neural progenitors for neurodegenerative disease modeling

Phenotypic drug discovery requires billions of cells for high-throughput screening (HTS) campaigns. Because up to several million different small molecules will be tested in a single HTS campaign, even small variability within the cell populations for screening could easily invalidate an entire campaign. Neurodegenerative assays are particularly challenging because neurons are post-mitotic and cannot be expanded for implementation in HTS. Therefore, HTS for neuroprotective compounds requires a cell type that is robustly expandable and able to differentiate into all of the neuronal subtypes involved in disease pathogenesis. Here, we report the derivation and propagation using only small molecules of human neural progenitor cells (small molecule neural precursor cells; smNPCs). smNPCs are robust, exhibit immortal expansion, and do not require cumbersome manual culture and selection steps. We demonstrate that smNPCs have the potential to clonally and efficiently differentiate into neural tube lineages, including motor neurons (MNs) and midbrain dopaminergic neurons (mDANs) as well as neural crest lineages, including peripheral neurons and mesenchymal cells. These properties are so far only matched by pluripotent stem cells. Finally, to demonstrate the usefulness of smNPCs we show that mDANs differentiated from smNPCs with LRRK2 G2019S are more susceptible to apoptosis in the presence of oxidative stress compared to wild-type. Therefore, smNPCs are a powerful biological tool with properties that are optimal for large-scale disease modeling, phenotypic screening, and studies of early human development.