Extracellular synaptic vesicles in the mouse heart

Do Media Extracellular Vesicles and Extracellular Vesicles Bound to the Extracellular Matrix Represent Distinct Types of Vesicles?

Mineralization-competent cells, including hypertrophic chondrocytes, mature osteoblasts, and osteogenic-differentiated smooth muscle cells secrete media extracellular vesicles (media vesicles) and extracellular vesicles bound to the extracellular matrix (matrix vesicles). Media vesicles are purified directly from the extracellular medium. On the other hand, matrix vesicles are purified after discarding the extracellular medium and subjecting the cells embedded in the extracellular matrix or bone or cartilage tissues to an enzymatic treatment. Several pieces of experimental evidence indicated that matrix vesicles and media vesicles isolated from the same types of mineralizing cells have distinct lipid and protein composition as well as functions. These findings support the view that matrix vesicles and media vesicles released by mineralizing cells have different functions in mineralized tissues due to their location, which is anchored to the extracellular matrix versus free-floating.

Characterizing Extracellular Vesicles and Their Diverse RNA Contents

Cells release nanometer-scale, lipid bilayer-enclosed biomolecular packages (extracellular vesicles; EVs) into their surrounding environment. EVs are hypothesized to be intercellular communication agents that regulate physiological states by transporting biomolecules between near and distant cells. The research community has consistently advocated for the importance of RNA contents in EVs by demonstrating that: (1) EV-related RNA contents can be detected in a liquid biopsy, (2) disease states significantly alter EV-related RNA contents, and (3) sensitive and specific liquid biopsies can be implemented in precision medicine settings by measuring EV-derived RNA contents. Furthermore, EVs have medical potential beyond diagnostics. Both natural and engineered EVs are being investigated for therapeutic applications such as regenerative medicine and as drug delivery agents. This review focuses specifically on EV characterization, analysis of their RNA content, and their functional implications. The NIH extracellular RNA communication (ERC) program has catapulted human EV research from an RNA profiling standpoint by standardizing the pipeline for working with EV transcriptomics data, and creating a centralized database for the scientific community. There are currently thousands of RNA-sequencing profiles hosted on the Extracellular RNA Atlas alone (Murillo et al., 2019), encompassing a variety of human biofluid types and health conditions. While a number of significant discoveries have been made through these studies individually, integrative analyses of these data have thus far been limited. A primary focus of the ERC program over the next five years is to bring higher resolution tools to the EV research community so that investigators can isolate and analyze EV sub-populations, and ultimately single EVs sourced from discrete cell types, tissues, and complex biofluids. Higher resolution techniques will be essential for evaluating the roles of circulating EVs at a level which impacts clinical decision making. We expect that advances in microfluidic technologies will drive near-term innovation and discoveries about the diverse RNA contents of EVs. Long-term translation of EV-based RNA profiling into a mainstay medical diagnostic tool will depend upon identifying robust patterns of circulating genetic material that correlate with a change in health status.

Visual identification of nerve terminals in living isolated skeletal muscle

1. The unmyelinated terminal branches of motor nerve fibres were clearly resolved in live, unstained skeletal muscles of the frog and of the mudpuppy (Necturus maculosus), using Nomarski optics. The observations were supplemented by several histological procedures, including electron microscopy, and by extracellular recordings from the nerve terminals. 2. In live motor nerve terminals of the mudpuppy one can see a series of varicosities, which in the electron microscope are shown to contain accumulations of synaptic vesicles. Junctional folds in the muscle fibres are confined to the areas opposite the varicosities. Terminal branches of the frog’s motor axon are also varicose, but the swellings are so closely spaced that they can be seen only after staining or by electron microscopy. 3. Nuclei of Schwann cells are recognized along living nerve terminals. Electrophoretic injection of a fluorescent dye, Procionyellow, into the cell bodies of Schwann cells enables one to see the distribution of their processes with the light microscope. 4. Visibility of terminal arborizations was improved by bathing nerve-muscle preparations in solutions of collagenase for 15 to 30 min, thereby removing much of the connective tissue. After longer collagenase treatment nerve terminals could be lifted off muscle fibres with a micropipette, thus exposing the postsynaptic membrane.

The innervation of the myometrium of the cynomolgus monkey (Macaca fascicularis). A quantitative electron-microscopic study

The autonomic innervation of the myometrium of Macaca fascicularis consists of bundles of unmyelinated nerve fibres running between the smooth muscle cells, and is therefore considered to be of the "fascicular (= unitary) type". Close contacts between nerve fibres and smooth muscle fibres were not found. Modification of the chromaffin method according to Tranzer and Richards made it possible to visualize the heterogeneity of the nerve fibres in a single bundle. The following fibre types were found to coexist: (1) noradrenergic fibres containing "synaptic" vesicles with a dense granule, (2) cholinergic fibres containing empty "synaptic vesicles", and (3) non-adrenergic non-cholinergic (NANC) fibres containing only or predominantly large dense-cored vesicles, which do not react with this method. Noradrenergic fibres are the most numerous (around 60%), followed by NANC fibres (30%) and cholinergic elements (around 10%). The distribution of these three types is similar in the cervix, the isthmus and the body of the uterus in pregnant and non-pregnant females.

Morphology of cardiac nerves in experimental infarction of rat hearts. II. Electron microscopical findings

Alterations of cardiac nerves in myocardial infarction were investigated by electron microscopy after differing intervals in 28 rats. During the first 4 h there are, in non-myelinated nerves within the myocardium, a swelling of the axoplasm with the occurrence of 'pale' axons and swelling of axonal mitochondria and neurosecretory granules. After bursting of the axolemma, these are spilled into the adjacent interstitial space. After 4 h first myelin figures are observed, and in some axons an accumulation of neurofilaments takes place. During the second to seventh day an extensive vesicular disintegration of axonal structures develops. Because of regressive changes, axons cannot be identified with certainty within the necrosis. After two or three weeks nerves with lamellar enfoldings of cytoplasmic processes corresponding to Büngner bands can be seen at the infarction border. These nerves may contain only a few residual axons. Myelinated nerves show a mainly vesicular disintegration. The results are discussed with regard to their functional significance and the special conditions of the animal model, in which ligature of the coronary artery may not only produce ischemia, but may also, by simultaneous ligature of the adjacent cardiac nerves, induce Wallerian degeneration.

Pinocytotic uptake and intracellular distribution of colloidal thorium dioxide by cultured sensory neurites

Sensory ganglia from 9-day chick embryos were grown on collagen coated coverslips for36 h in the presence of nerve growth factor, producing a profuse neuritic outgrowth. The cultures were then incubated for varying periods in a colloidal suspension of thorium dioxide, and the pinocytotic uptake of this marker was followed by electron microscopy. Following brief exposures (3 min), most of the labelled organelles consisted of smooth surfaced vesicles and vacuoles; with longer exposures, the bulk of the marker accumulated first in cup-shaped pre-multivesticular bodies and ultimately in multivesicular bodies. The marker was also taken up into coated vesicles, dense-cored and electron lucent tubules,dense-cored vesicles and dense bodies of the multi-layered myelin body configuration. In addition, evidence suggestive of exocytosis was also obtained; views of apparent fusion of labelled multivesicular bodies with the plasmalemma involving extrusion of vesiclesand marker particles into the extracellular space were regularly encountered following long exposures.