Tag Archives: ultrastructure

SEM vs. TEM

SEM vs. TEM is a tradeoff of convenience, resolution, cost and speed. The very physics of SEM signal integration means that the fundamental acquisition time for large canonical volume datasets are incompatible with 5 year grant cycles. SEM based approaches can potentially rival TEM, but dwell time/pixel increases logarithmically with resolution.

To give you some idea for the resolution differences at routine capture speeds, both of these above images capture a region within the inner plexiform layer of retina, looking at bipolar cell terminals. The TEM image was captured at a standard operating resolution of 2nm/pixel. The SEM image was captured at 16nm/pixel. You cannot see any gap junctions that might be present in the SEM image and you can only infer or guess at synaptic ribbons. And look at the texture!

You *can* get better resolution with SEM, but as I said before, the capture time increases logarithmically. To accomplish what we perform in 8-10 hours with a TEM, would take 108-115 hours on a current, cutting edge multi beam SEM. There are many other advantages of TEM including the ability to capture higher resolution images faster, be able to re-image in goniometric tilt series, be able to integrate molecular markers inside connectome volumes, and a TEM is about 1/3rd the cost of an SEM. Also, SEM images tend to be texturally poor as they are made from capturing electron backscatter of surfaces rather than made by projection of electrons through a small volume, and there is tremendous value in the texture of ultrastructural images. Ergo, this is why we use TEM.

This is not to say that SEM is not a great tool. It is just not the best tool for large scale connectomics where you have to have the resolution to capture all synapses and gap junctions, over large areas. For smaller volumes that do not require a canonical sampling of cell classes, SEM is absolutely an appropriate tool.

This content was originally published on Jonesblog.

The Rod-Cone Crossover Connectome of Mammalian Bipolar Cells

We have a new publication out (direct link), The rod-cone crossover connectome of mammalian bipolar cells authored by Scott Lauritzen, Crystal Sigulinsky, James Anderson, Michael Kalloniatis, Noah Nelson, Danny Emrich, Chris Rapp, Nicolas McCarthy, Ethan Kerzner, Mariah Meyer, Bryan W. Jones, and Robert Marc.

Abstract: The basis of cross-suppression between rod and cone channels has long been an enigma. Using rabbit retinal connectome RC1, we show that all cone bipolar cell (BC) classes inhibit rod BCs via amacrine cell (AC) motifs (C1-6); that all cone BC classes are themselves inhibited by AC motifs (R1-5, R25) driven by rod BCs. A sparse symmetric AC motif (CR) is presynaptic and postsynaptic to both rod and cone BCs. ON cone BCs of all classes drive inhibition of rod BCs via motif C1 wide-field GABAergic ACs (γACs) and motif C2 narrow field glycinergic ON ACs (GACs). Each rod BC receives ≈ 10 crossover AC synapses and each ON cone BC can target ≈ 10 or more rod BCs via separate AC processes. OFF cone BCs mediate monosynaptic inhibition of rod BCs via motif C3 driven by OFF γACs and GACs and disynaptic inhibition via motifs C4 and C5 driven by OFF wide-field γACs and narrow-field GACs, respectively. Motifs C4 and C5 form halos of 60-100 inhibitory synapses on proximal dendrites of AI γACs. Rod BCs inhibit surrounding arrays of cone BCs through AII GAC networks that access ON and OFF cone BC patches via motifs R1, R2, R4 R5 and a unique ON AC motif R3 that collects rod BC inputs and targets ON cone BCs. Crossover synapses for motifs C1, C4, C5 and R3 are 3-4x larger than typical feedback synapses, which may be a signature for synaptic winner-take-all switches.

2-nm Resolution Anatomy of Retinal Neuro-Glial-Vascular Architecture

This abstract was presented today, May 2th at the 2016 Association for Research in Vision and Opthalmology (ARVO) meetings in Seattle, Washington by Jefferson R. Brown, Rebecca L. Pfeiffer, Crystal Sigulinsky, Felix Vazquez-Chona, Daniel Emrich, Bryan W. Jones, Robert E. Marc.

Abstract Number: 995

Author Block: Jefferson R. Brown, Rebecca L. Pfeiffer, Crystal Sigulinsky, Felix Vazquez-Chona, Daniel Emrich, Bryan W. Jones, Robert E. Marc
1 Dept of Ophthalmology, University of Utah, Salt Lake City, Utah, United States

Disclosure Block:Jefferson R. Brown, None; Rebecca L. Pfeiffer, None; Crystal Sigulinsky, None; Felix Vazquez-Chona, None; Daniel Emrich, None; Bryan W. Jones, None; Robert E. Marc, Signature Immunologics (Code I (Personal Financial Interest) )

Purpose:Retinal vasculature is strongly affected by degenerative pathologies and in turn, may also contribute to their progression. However, much of what we understand about the normal, healthy interaction between neurons, glia, and blood vessels at the ultrastructural level is limited to single section electron microscopy. The technology of serial section transmission electron microscopy (ssTEM) extends the high definition of TEM imaging into three dimensions to create volumes, allowing for more thorough visualization and analysis of the vascular-glial-neuronal complex.

Methods:RC2 is a 40TB ssTEM volume of over 1,400 horizontal sections of retinal tissue derived from an adult female C57BL/6J mouse. The tissue sample is 250 um in diameter and spans the outer nuclear layer to the vitreal surface. Baseline resolution is 2.18nm per pixel. Visualization, navigation and metadata annotations of the database are made via the Viking software suite.

Results:Much of the retinal vascular basement membrane directly contacts Muller cells. In the ganglion cell layer, direct basement membrane contact with astrocytes is frequent. Microglia commonly contact the basement membrane, and occasionally direct contact of neurons onto basement membrane was observed. Full 3D reconstruction of all vascular pathways with associated endothelia and pericytes within the volume was completed, demonstrating that all the retinal capillary layers are continuous with one another [Figure].

Conclusions:The presence of occasional direct neuronal contact onto vascular basement membrane supports earlier work by Ochs and colleagues (2000) and suggests the blood-retina barrier does not universally involve retinal glia. However, since such contacts are extremely sparse, it remains to be seen whether this finding has biologic significance, though their existence suggests significance. The RC2 volume is a valuable resource to aid in discovery of defining characteristics of wild type neurovascular architecture.


The intro figure is a side view of reconstruction of all vasculature within the RC2 volume. Vessels at the top of the figure correspond to the outer plexiform layer, while those at the bottom correspond to the ganglion cell layer. This capillary plexus is one continuous structure. Visualization by VikingView software.

A Targeted Inhibitor Of The Alternative Complement Pathway Accelerates Recovery From Smoke-Induced Ocular Injury

We have a new publication out, A Targeted Inhibitor Of The Alternative Complement Pathway Accelerates Recovery From Smoke-Induced Ocular Injury authored by Alex Woodell, Bryan W. Jones, Tucker Williamson, Gloriane Schnabolk, Stephen Tomlinson, Carl Atkinson and Bärbel Rohrer.

Abstract:
PURPOSE. Morphological and genetic evidence exists that an overactive complement system driven by the complement alternative pathway (CAP) is involved in pathogenesis of age- related macular degeneration (AMD). Smoking is the only modifiable risk factor for AMD. As we have shown that smoke-related ocular pathology can be prevented in mice that lack an essential activator of CAP, we ask here whether this pathology can be reversed by increasing inhibition in CAP.

METHODS. Mice were exposed to either cigarette smoke (CS) or filtered air (6 hours/day, 5 days/week, 6 months). Smoke-exposed animals were then treated with the CAP inhibitor (CR2-fH) or vehicle control (PBS) for 3 months. Spatial frequency and contrast sensitivity were assessed by optokinetic response paradigms at 6 and 9 months; additional readouts included assessment of retinal morphology by electron microscopy (EM) and gene expression analysis by quantitative PCR.

RESULTS. The CS mice treated with CR2-fH showed significant improvement in contrast threshold compared to PBS-treated mice, whereas spatial frequency was unaffected by CS or pharmacological intervention. Treatment with CR2-fH in CS animals reversed thinning of the retina observed in PBS-treated mice as analyzed by spectral-domain optical coherence tomography, and reversed most morphological changes in RPE and Bruch’s membrane seen in CS animals by EM.

CONCLUSIONS. Taken together, these findings suggest that CAP inhibitors not only prevent, but have the potential to accelerate, the clearance of complement-mediated ocular injury. Improving our understanding of the regulation of the CAP pathway is paramount to developing novel treatment approaches for AMD.

Retinal Remodeling in Human Retinitis Pigmentosa

We have a new publication out (Direct Link, Free Open Access), Retinal Remodeling in Human Retinitis Pigmentosa authored by Bryan W. Jones, Rebecca Pfeiffer, Drew Ferrell, Carl Watt, Michael Marmor and Robert Marc.

Abstract: Retinitis Pigmentosa (RP) in the human is a progressive, currently irreversible neural degenerative disease usually caused by gene defects that disrupt the function or architecture of the photoreceptors. While RP can initially be a disease of photoreceptors, there is increasing evidence that the inner retina becomes progressively disorganized as the outer retina degenerates. These alterations have been extensively described in animal models, but remodeling in humans has not been as well characterized. This study, using computational molecular phenotyping (CMP) seeks to advance our understanding of the retinal remodeling process in humans. We describe cone mediated preservation of overall topology, retinal reprogramming in the earliest stages of the disease in retinal bipolar cells, and alterations in both small molecule and protein signatures of neurons and glia. Furthermore, while Müller glia appear to be some of the last cells left in the degenerate retina, they are also one of the first cell classes in the neural retina to respond to stress which may reveal mechanisms related to remodeling and cell death in other retinal cell classes. Also fundamentally important is the finding that retinal network topologies are altered. Our results suggest interventions that presume substantial preservation of the neural retina will likely fail in late stages of the disease. Even early intervention offers no guarantee that the interventions will be immune to progressive remodeling. Fundamental work in the biology and mechanisms of disease progression are needed to support vision rescue strategies.

Store-Operated Calcium Entry In Müller Glia Is Controlled By Synergistic Activation Of TRPC And Orai Channels

We have a new publication out as collaborators with colleages, Store-Operated Calcium Entry In Müller Glia Is Controlled By Synergistic Activation Of TRPC And Orai Channels authored by Tünde Molnár, Oleg Yarishkin, Peter Barabas, Anthony Iuso, Bryan W. Jones, Robert Marc, Tam Phuong, and David Krizaj.

Bonus, we got the cover!  The image was created by Tam Phuong.

 

Significance: Store-operated Ca2+ signaling represents a major signaling pathway and source of cytosolic Ca2+ in astrocytes. Here, we show that the store-operated response in Müller cells, radial glia that perform key structural, signaling, osmoregulatory and mechanosensory functions within the retina, is mediated through synergistic activation of TRPC and Orai channels. The endfoot disproportionately expresses the depletion sensor STIM1, contains an extraordinarily high density of ER cisternae that shadow neuronal, astrocyte, vascular and axonal structures, interface with mitochondria but also originates SOCE-induced transcellular Ca2+ waves that propagate glial excitation into the proximal retina. These results identify a molecular mechanism that underlies complex interactions between the plasma membrane and calcium stores and contributes to radial glial function, regulation and response to mechanical stress.

Abstract: The endoplasmic reticulum (ER) is at the epicenter of astrocyte Ca2+ signaling. We sought to identify the molecular mechanism underlying store-operated calcium entry (SOCE) that repletes ER Ca2+ stores in mouse Müller cells. Store depletion, induced through blockade of sequestration transporters in Ca2+-free saline, induced synergistic activation of canonical transient receptor potential (TRPC1) and Orai channels. Store-operated TRPC1 channels were identified by their electrophysiological properties, pharmacological blockers and ablation of the Trpc1 gene. ICRAC (Ca2+ release-activated) currents were identified by ion permeability, voltage-dependence and sensitivity to selective Orai antagonists Synta66 and GSK7975A. Depletion-evoked calcium influx was initiated at the Müller endfoot and apical process, triggering centrifugal propagation of Ca2+ waves into the cell body. EM analysis of the endfoot compartment showed high-density ER cisternae that shadow retinal ganglion cell (RGC) somata and axons, protoplasmic astrocytes, vascular endothelial cells and ER-mitochondrial contacts at the vitreal surface of the endfoot. The mouse retina expresses transcripts encoding both Stim and all known Orai genes; Müller glia predominantly express STIM1 whereas STIM2 is mainly confined to the outer plexiform and retinal ganglion cell layers. Elimination of TRPC1 facilitated Müller gliosis induced by the elevation of intraocular pressure (IOP), suggesting that TRPC channels might play a neuroprotective role during mechanical stress. These findings expand the current knowledge about store-operated signaling in astroglia, as well as calcium signaling pathways in Müller astroglia and functional roles these cells play in retinal physiology and pathology.

Seasonal And Post-Trauma Remodeling Of The Ground Squirrel Retina

We have a new publication out, Seasonal and post-trauma remodeling in cone-dominant ground squirrel retina authored by Dana Merriman, Ben Sajdak, Wei Li and Bryan W. Jones.

Abstract:

With a photoreceptor mosaic containing ∼85% cones, the ground squirrel is one of the richest known mammalian sources of these important retinal cells. It also has a visual ecology much like the human’s. While the ground squirrel retina is understandably prominent in the cone biochemistry, physiology, and circuitry literature, far less is known about the remodeling potential of its retinal pigment epithelium, neurons, macroglia, or microglia. This review aims to summarize the data from ground squirrel retina to this point in time, and to relate them to data from other brain areas where appropriate. We begin with a survey of the ground squirrel visual system, making comparisons with traditional rodent models and with human. Because this animal’s status as a hibernator often goes unnoticed in the vision literature, we then present a brief primer on hibernation biology. Next we review what is known about ground squirrel retinal remodeling concurrent with deep torpor and with rapid recovery upon re-warming. Notable here is rapidly-reversible, temperature-dependent structural plasticity of cone ribbon synapses, as well as pre- and post-synaptic plasticity throughout diverse brain regions. It is not yet clear if retinal cell types other than cones engage in torpor-associated synaptic remodeling. We end with the small but intriguing literature on the ground squirrel retina’s remodeling responses to insult by retinal detachment. Notable for widespread loss of (cone) photoreceptors, there is surprisingly little remodeling of the RPE or Müller cells. Microglial activation appears minimal, and remodeling of surviving second- and third-order neurons seems absent, but both require further study. In contrast, traumatic brain injury in the ground squirrel elicits typical macroglial and microglial responses. Overall, the data to date strongly suggest a heretofore unrecognized, natural checkpoint between retinal deafferentiation and RPE and Müller cell remodeling events. As we continue to discover them, the unique ways by which ground squirrel retina responds to hibernation or injury may be adaptable to therapeutic use.

In Situ Metabolomic Signatures Of Neuroprotection, Apoptosis, And Microglial Phagocytosis

This abstract was presented July 1st at the 11th International Converence of the Metabolomics Society at the University of California, Davis by Felix Vazquez-Chona, Drew Ferrell, Bryan W. Jones and Robert E. Marc.

 

Metabolic dysregulation is an early hallmark of neurodegenerative diseases including Alzheimer’s disease and age-related macular degeneration. Mapping metabolic adaptation with cellular resolution and tissue- wide context is crucial to define networks regulating neuronal survival, cell death progression, and immune cell response.

Computational Molecular Phenotyping (CMP) explores the amine metabolome (amino acids and amines). Technically, CMP metabolomics combines amine metabolite trapping, ultrathin microscopy (50-200 nm), immunodetection, pattern recognition, and clustering algorithms. Here we mapped the in situ distribution of over 30 core amine metabolites in retinal cells challenged by light-induced oxidative stress. Metabolomic profiles were phenotyped using ultrastructural, biochemical, and proteomic indices of oxidative stress.

CMP enabled precise visualization of >30 metabolites in every retinal cell. CMP resolved and phenotyped metabolomic profiles to specific degeneration and microglial functional states in the light-damaged retina. Cone photoreceptor survival correlated with enhanced antioxidant glutathione content. Rod photoreceptor apoptosis coincided with rapid depletion of organic osmolytes followed by nuclear import of cationic arginine metabolites. Delay in cell death increased necrosis and DNA damage-induced apoptosis. Microglial chemotaxis enhanced distinct signatures of glutamate and glutathione metabolism; whereas, phagocytosis coinduced classic (M1) and alternative (M2) arginine metabolites of macrophage activation.

CMP discovers and phenotypes cell classes, tracks cell state, and maps disease with single-cell resolution in any tissue or organism.

The Alternative Complement Pathway Deficiency Amerliorates Chronic Smoked-Induced Functional And Morphological Ocular Injury

Alex Woodell, Beth Coughlin, Kannan Kunchithapautham, Sarah Casey, Tucker Williamson, W. Drew Ferrell,  Carl Atkinson, Bryan Jones and Baerbel Rohrer have a new manuscript out, The Alternative Complement Pathway Deficiency Amerliorates Chronic Smoked-Induced Functional And Morphological Ocular Injury in PLOS One.

The short story is: Don’t smoke.  But then you knew that.  Where this paper contributes is that it provides clear findings that show ocular pathologies generated by cigarette smoke are dependent upon activation of the immune system, in particular complement and the alternative pathway which are critical findings in the treatment of AMD.