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1985 Janelia Publications

Showing 11-20 of 1985 results
08/25/21 | Regulated exocytosis: Renal Aquaporin-2 3D Vesicular Network Organization and Association with F-actin.
Holst MR, Gammelgaard L, Aaron J, Login FH, Rajkumar S, Hahn U, Nejsum LN
American Journal of Physiology: Cell Physiology. 2021 Aug 25:. doi: 10.1152/ajpcell.00255.2021

Regulated vesicle exocytosis is a key response to extracellular stimuli in diverse physiological processes; including hormone regulated short-term urine concentration. In the renal collecting duct, the water channel aquaporin-2 localizes to the apical plasma membrane as well as small, sub-apical vesicles. In response to stimulation with the antidiuretic hormone, arginine vasopressin, aquaporin-2 containing vesicles fuse with the plasma membrane, which increases collecting duct water reabsorption and thus, urine concentration. The nano-scale size of these vesicles has limited analysis of their 3D organization. Using a cell system combined with 3D super resolution microscopy, we provide the first direct analysis of the 3D network of aquaporin-2 containing exocytic vesicles in a cell culture system. We show that aquaporin-2 vesicles are 43 ± 3nm in diameter, a size similar to synaptic vesicles, and that one fraction of AQP2 vesicles localized with the sub-cortical F-actin layer and the other localized in between the F-actin layer and the plasma membrane. Aquaporin-2 vesicles associated with F-actin and this association was enhanced in a serine 256 phospho-mimic of aquaporin-2, whose phosphorylation is a key event in antidiuretic hormone-mediated aquaporin-2 vesicle exocytosis.

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08/24/21 | Campylobacter jejuni Triggers Signaling through Host Cell Focal Adhesions To Inhibit Cell Motility.
Klappenbach CM, Negretti NM, Aaron J, Chew T, Konkel ME
mBio. 2021 Aug 24:e0149421. doi: 10.1128/mBio.01494-21

Campylobacter jejuni is a major foodborne pathogen that exploits the focal adhesions of intestinal cells to promote invasion and cause severe gastritis. Focal adhesions are multiprotein complexes involved in bidirectional signaling between the actin cytoskeleton and the extracellular matrix. We investigated the dynamics of focal adhesion structure and function in C. jejuni-infected cells using a comprehensive set of approaches, including confocal microscopy of live and fixed cells, immunoblotting, and superresolution interferometric photoactivated localization microscopy (iPALM). We found that C. jejuni infection of epithelial cells results in increased focal adhesion size and altered topology. These changes resulted in a persistent modulatory effect on the host cell focal adhesion, evidenced by an increase in cell adhesion strength, a decrease in individual cell motility, and a reduction in collective cell migration. We discovered that C. jejuni infection causes an increase in phosphorylation of paxillin and an alteration of paxillin turnover at the focal adhesion, which together represent a potential mechanistic basis for altered cell motility. Finally, we observed that infection of epithelial cells with the C. jejuni wild-type strain in the presence of a protein synthesis inhibitor, a C. jejuni CadF and FlpA fibronectin-binding protein mutant, or a C. jejuni flagellar export mutant blunts paxillin phosphorylation and partially reestablishes individual host cell motility and collective cell migration. These findings provide a potential mechanism for the restricted intestinal repair observed in C. jejuni-infected animals and raise the possibility that bacteria targeting extracellular matrix components can alter cell behavior after binding and internalization by manipulating focal adhesions. Campylobacter jejuni is a major foodborne pathogen that causes severe gastritis. We investigated the dynamics of focal adhesion structure and function in C. jejuni-infected epithelial cells. Focal adhesions act as signaling complexes that connect the extracellular matrix to the intracellular cytoskeleton. The key findings of this study show that C. jejuni changes the structure (size and position), composition, and function of cellular focal adhesions using a combination of virulence factors. Mechanistically, we found that the changes in focal adhesion dynamics are dependent upon the activation of host cell signaling pathways, which affect the assembly and disassembly of cellular proteins from the focal adhesion. To summarize, we have identified a new cellular phenotype in C. jejuni-infected cells that may be responsible for the restricted intestinal repair observed in C. jejuni-infected animals.

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08/24/21 | Campylobacter jejuni Triggers Signaling through Host Cell Focal Adhesions To Inhibit Cell Motility.
Klappenbach CM, Negretti NM, Aaron J, Chew T, Konkel ME
mBio. 2021 Aug 24;12(4):e0149421. doi: 10.1128/mBio.01494-21

Campylobacter jejuni is a major foodborne pathogen that exploits the focal adhesions of intestinal cells to promote invasion and cause severe gastritis. Focal adhesions are multiprotein complexes involved in bidirectional signaling between the actin cytoskeleton and the extracellular matrix. We investigated the dynamics of focal adhesion structure and function in C. jejuni-infected cells using a comprehensive set of approaches, including confocal microscopy of live and fixed cells, immunoblotting, and superresolution interferometric photoactivated localization microscopy (iPALM). We found that C. jejuni infection of epithelial cells results in increased focal adhesion size and altered topology. These changes resulted in a persistent modulatory effect on the host cell focal adhesion, evidenced by an increase in cell adhesion strength, a decrease in individual cell motility, and a reduction in collective cell migration. We discovered that C. jejuni infection causes an increase in phosphorylation of paxillin and an alteration of paxillin turnover at the focal adhesion, which together represent a potential mechanistic basis for altered cell motility. Finally, we observed that infection of epithelial cells with the C. jejuni wild-type strain in the presence of a protein synthesis inhibitor, a C. jejuni CadF and FlpA fibronectin-binding protein mutant, or a C. jejuni flagellar export mutant blunts paxillin phosphorylation and partially reestablishes individual host cell motility and collective cell migration. These findings provide a potential mechanism for the restricted intestinal repair observed in C. jejuni-infected animals and raise the possibility that bacteria targeting extracellular matrix components can alter cell behavior after binding and internalization by manipulating focal adhesions. Campylobacter jejuni is a major foodborne pathogen that causes severe gastritis. We investigated the dynamics of focal adhesion structure and function in C. jejuni-infected epithelial cells. Focal adhesions act as signaling complexes that connect the extracellular matrix to the intracellular cytoskeleton. The key findings of this study show that C. jejuni changes the structure (size and position), composition, and function of cellular focal adhesions using a combination of virulence factors. Mechanistically, we found that the changes in focal adhesion dynamics are dependent upon the activation of host cell signaling pathways, which affect the assembly and disassembly of cellular proteins from the focal adhesion. To summarize, we have identified a new cellular phenotype in C. jejuni-infected cells that may be responsible for the restricted intestinal repair observed in C. jejuni-infected animals.

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08/20/21 | Imaging Africa: a strategic approach to optical microscopy training in Africa.
Reiche MA, Warner DF, Aaron J, Khuon S, Fletcher DA, Hahn K, Rogers KL, Mhlanga M, Koch A, Quaye W, Chew T
Nature Methods. 2021 Aug 20;18(8):847-855. doi: 10.1038/s41592-021-01227-y
01/08/18 | Development and Applications of Fluorescent Proteins for Correlative Light and Electron Microscopy
Paez-Segala MG, Wang Y, Iyer N, Li W, Rivlin PK, Looger LL
Microscopy and Microanalysis. 01/2018;24(S1):2318 - 2319. doi: 10.1017/S1431927618012072

Recent advances in super-resolution microscopy have pushed the resolution limit of light microscopy closer to that of electron microscopy. However, as they invariably rely on fluorescence, light microscopy techniques only visualize whatever gets labeled. On the other hand, while electron microscopy reveals cellular structures at the highest resolution, it offers no specificity. The information gap between the two imaging modalities can only be bridged by correlative light and electron microscopy (CLEM). Previously we have developed a probe (mEos4) whose fluorescence and photoconversion survive 0.5-1% OsO4 fixation, allowing super-resolution visualization of organelles and fused proteins in the context of resinembedded ultrastructure in both transmission EM (TEM) and scanning EM (SEM) [1,2].

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07/30/20 | Optimization of Fluorescent Proteins and Techniques for In-resin Correlative Light and Electron Microscopy
Paez-Segala M, Wang Y, Iyer N, Li W, Rivlin P, Looger L
Microscopy and Microanalysis. 07/2020;26:1036–1039. doi: 10.1017/S143192762001675X

Correlative light and electron microscopy (CLEM) combines the power of electron microscopy, with its excellent resolution and contrast, with that of fluorescence imaging, which allows the staining of specific molecules, organelles, and cell populations. Fluorescence imaging is also readily compatible with live cells and behaving animals, facilitating real-time visualization of cellular processes, potentially followed by electron microscopic reconstruction. Super-resolution single-molecule localization microscopy is a relatively new modality that harnesses the ability of some fluorophores to photoconvert, through which localization precision better than Abbe’s diffraction limit is achieved through iterative high-resolution localization of single-molecule emitters. Here we describe our lab’s recent progress in the development of reagents and techniques for super-resolution single-molecule localization CLEM and their applications to biological problems.

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08/09/21 | Optogenetics
Looger LL, Maria G. Paez Segala
Molecular Imaging: Principles and Practice, 2nd Edition:

To truly understand biological systems, one must possess the ability to selectively manipulate their parts and observe the outcome. (For purposes of this review, we refer mostly to targets of neuroscience; however, the principles covered here largely extend to myriad samples from microbes to plants to the intestine, etc.).

Drugs are the most commonly employed way of introducing such perturbations, but they act on endogenous proteins that frequently exist in multiple cell types, complicating the interpretation of experiments. Whatever the applied stimulus, it is best to introduce optimized exogenous reagents into the systems under studydenabling manipulations to be targeted to speci!c cells and pathways. (It is also possible to target manipulations through other means, such as drugs that acquire cell-type speci!city through targeting via antibodies and/or cell surface receptor ligands, but as far as we are aware, existing reagents fall short in terms of necessary speci!city.) Many types of perturbations are useful in living systems and can be divided into rough categories such as the following: depolarize or hyperpolarize cells, induce or repress the activity of a speci!c pathway, induce or inhibit expression of a particular gene, activate or repress a speci!c protein, degrade a speci!c protein, etc. User-supplied triggers for such manipulations to occur include the following: addition of a small molecule (“chemogenetics”dideally inert on endogenous proteins) [1], sound waves (“sonogenetics”) [2], alteration of temperature (“thermogenetics”d almost exclusively used for small invertebrates) [3], and light (“optogenetics”). There are reports of using magnetic !elds (“magnetogenetics”) [4], but there is no evidence that such effects are reproducible or even physically possible [5,6]. Of these, the most commonly used, for multiple reasons, is light.

Many factors make light an ideal user-controlled stimulus for the manipulation of samples. Light is quickly delivered, and most light-sensitive proteins and other molecules respond quickly to light stimuli, making many optogenetic systems relatively rapid in comparison to, for instance, drug-modulated systems. Light is also quite easy to deliver in localized patterns, allowing for targeted stimulation. Multiple wavelengths can be delivered separately to distinct (or overlapping) regions, potentially allowing combinatorial control of diverse components. Finally, light can be delivered to shallow brain regions (and peripheral sites) relatively noninvasively, and to deeper brain regions with some effort.

However, there are also a number of shortcomings of using light for control. Robust and uniform penetration of light into the sample is the most signi!cant concern. For systems requiring modulation of many cells, particularly at depth, the use of systems controlled by small molecule drugs would generally be recommended instead of optogenetic approaches. When light is delivered through the use of !bers, lenses, or other optical devices, such interventions can produce signi!- cant cellular death, scar formation, and biofouling. The foreign-body response of tissue to objects triggers substantial molecular alterations, the implications of which are incompletely de!ned, but can involve reactive astrogliosis, oxidative stress, and perturbed vascularization. Head-mounted lightdelivery devices can be heavy and/or restrictive, and thus perturb behavior, particularly for small animals (e.g., mouse behavior is much more disrupted than rat behavior). More generally, all light causes tissue heating, which can have dramatic effects on cell health, physiology, and animal behavior. This is most concerning for tiny animals such as "ies. Light itself also damages tissue, most obviously through photochemistry (e.g., oxidation and radicalization) and photobleaching of critical endogenousmolecules. Furthermore, of course, light is ubiquitous, meaning that the sample is never completely unstimulated, despite precautions. Light passes through the eyes into the brain with surprising ease, and even through the skull with modest ef!cacy [7]dwhich can disrupt animal behavior (as can the converse: stimulating light in the brain perceived as a visual stimulus through the back of the eyes.) Light-responsive proteins exist in all samples, particularly in the eyes but to some extent in all tissuesdnotably, deep-brain photoreceptors [8].

The use of optogenetic tools has accelerated research on many fronts in disparate !elds. Additional, perhaps most, limitations on the utility of optogenetics must, however, be placed squarely on the shortcomings of the current suite of tools (and potential inherent limits in their performance.) The vast majority of optogenetic effectors are gated by blue light, which has signi!cant penetration issues and can be phototoxic under high intensity; redder wavelengths would in general be preferred. Furthermore, multiplexing requires tools making use of other parts of the visible spectrum (and redder wavelengths). A related issue is that most chromophores for optogenetic reagents have very broad action spectra (w250 nm bandwidth for retinal; w200 nm bandwidth for "avin), complicating both multiplexing and their use alongside many optical imaging reagentsdnarrower action spectra would be preferred for effectors in most situations. More generally, the current classes of optogenetic effectors are few, mostly limited to (1) channels and pumps (most with poor ion selectivity), (2) dimerizers, and (3) a handful of enzymes. The number of optogenetic tools that perform a very speci!c function in cells is small. Although progress has undeniably been made, much additional research and engineering will be required to dramatically expand the optogenetic toolkit.

Rather than providing a survey of research !ndings, this review covers general considerations of optogenetics experiments, and then focuses largely on molecular tools: the existing suite, their features and limitations, and goals for the creation and validation of additional reagents.

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08/16/21 | Spatially patterned excitatory neuron subtypes and projections of the claustrum.
Erwin SR, Bristow BN, Sullivan KE, Kendrick RM, Marriott B, Wang L, Clements J, Lemire AL, Jackson J, Cembrowski MS
eLife. 2021 Aug 16;10:. doi: 10.7554/eLife.68967

The claustrum is a functionally and structurally complex brain region, whose very spatial extent remains debated. Histochemical-based approaches typically treat the claustrum as a relatively narrow anatomical region that primarily projects to the neocortex, whereas circuit-based approaches can suggest a broader claustrum region containing projections to the neocortex and other regions. Here, in the mouse, we took a bottom-up and cell-type-specific approach to complement and possibly unite these seemingly disparate conclusions. Using single-cell RNA-sequencing, we found that the claustrum comprises two excitatory neuron subtypes that are differentiable from the surrounding cortex. Multicolor retrograde tracing in conjunction with 12-channel multiplexed in situ hybridization revealed a core-shell spatial arrangement of these subtypes, as well as differential downstream targets. Thus, the claustrum comprises excitatory neuron subtypes with distinct molecular and projection properties, whose spatial patterns reflect the narrower and broader claustral extents debated in previous research. This subtype-specific heterogeneity likely shapes the functional complexity of the claustrum.

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08/12/21 | The cAMP effector PKA mediates Moody GPCR signaling in blood-brain barrier formation and maturation.
Li X, Fetter R, Schwabe T, Jung C, Liu L, Steller H, Gaul U
eLife. 2021 Aug 12;10:. doi: 10.7554/eLife.68275

The blood-brain barrier (BBB) of is comprised of a thin epithelial layer of subperineural glia (SPG), which ensheath the nerve cord and insulate it against the potassium-rich hemolymph by forming intercellular septate junctions (SJs). Previously, we identified a novel Gi/Go protein-coupled receptor (GPCR), Moody, as a key factor in BBB formation at the embryonic stage. However, the molecular and cellular mechanisms of Moody signaling in BBB formation and maturation remain unclear. Here, we identify cAMP-dependent protein kinase A (PKA) as a crucial antagonistic Moody effector that is required for the formation, as well as for the continued SPG growth and BBB maintenance in the larva and adult stage. We show that PKA is enriched at the basal side of the SPG cell and that this polarized activity of the Moody/PKA pathway finely tunes the enormous cell growth and BBB integrity. Moody/PKA signaling precisely regulates the actomyosin contractility, vesicle trafficking, and the proper SJ organization in a highly coordinated spatiotemporal manner. These effects are mediated in part by PKA's molecular targets MLCK and Rho1. Moreover, 3D reconstruction of SJ ultrastructure demonstrates that the continuity of individual SJ segments, and not their total length, is crucial for generating a proper paracellular seal. Based on these findings, we propose that polarized Moody/PKA signaling plays a central role in controlling the cell growth and maintaining BBB integrity during the continuous morphogenesis of the SPG secondary epithelium, which is critical to maintain tissue size and brain homeostasis during organogenesis.

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08/11/21 | Structured patterns of activity in pulse-coupled oscillator networks with varied connectivity.
Kadhim KL, Hermundstad AM, Brown KS
PLoS One. 2021 Aug 11;16(8):e0256034. doi: 10.1371/journal.pone.0256034

Identifying coordinated activity within complex systems is essential to linking their structure and function. We study collective activity in networks of pulse-coupled oscillators that have variable network connectivity and integrate-and-fire dynamics. Starting from random initial conditions, we see the emergence of three broad classes of behaviors that differ in their collective spiking statistics. In the first class ("temporally-irregular"), all nodes have variable inter-spike intervals, and the resulting firing patterns are irregular. In the second ("temporally-regular"), the network generates a coherent, repeating pattern of activity in which all nodes fire with the same constant inter-spike interval. In the third ("chimeric"), subgroups of coherently-firing nodes coexist with temporally-irregular nodes. Chimera states have previously been observed in networks of oscillators; here, we find that the notions of temporally-regular and chimeric states encompass a much richer set of dynamical patterns than has yet been described. We also find that degree heterogeneity and connection density have a strong effect on the resulting state: in binomial random networks, high degree variance and intermediate connection density tend to produce temporally-irregular dynamics, while low degree variance and high connection density tend to produce temporally-regular dynamics. Chimera states arise with more frequency in networks with intermediate degree variance and either high or low connection densities. Finally, we demonstrate that a normalized compression distance, computed via the Lempel-Ziv complexity of nodal spike trains, can be used to distinguish these three classes of behavior even when the phase relationship between nodes is arbitrary.

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