Endopeptidase-24.11, a Cell-Surface Peptidace of Central Nervous System Neurons, Is Expressed by Schwann Cells in the Pig Peripheral Nervous System

Endopeptidase-24.11 is a 90-kDa surface glycoprotein with the ability to hydrolyze a variety of biologically active peptides. Interest in this enzyme is based on the consensus that it may play a role in the termination of peptide signals in the central nervous system. In the present study, we have investigated the distribution of endopeptidase-24.11 in two nerves of the peripheral nervous system of newborn pigs: the sciatic, composed of a mixture of myelinated and nonmyelinated axons, and cervical sympathetic trunk in which greater than 99% of the axons are nonmyelinated. The endopeptidase was monitored enzymatically, as well as by immunoblotting and immunocytochemistry using mono- and polyclonal anti-endopeptidase antibodies. Endopeptidase-24.11 was detected in both the sciatic nerve and the cervical sympathetic trunk. Membrane preparations from sciatic nerve hydrolyzed 125I-insulin B-chain, and more than 50% of the activity was inhibited by phosphoramidon with an IC50 concentration of 3.2 nM. Moreover, a 90-kDa polypeptide was detected by immunoblotting of sciatic nerve membranes. The type of cells expressing the endopeptidase was determined by immunohistochemistry. In teased nerve preparations, these cells were identified morphologically as myelin- and non-myelin-forming Schwann cells. Endopeptidase-24.11 was also expressed by cultured Schwann cells from sciatic nerve and cervical sympathetic trunk maintained for 3 h in vitro. The presence of endopeptidase-24.11 on the Schwann cell surface raises the possibility of a potential role for the enzyme in nerve development and/or regeneration.     

Mouse Forward Genetics in the Study of the Peripheral Nervous System and Human Peripheral Neuropathy

Forward genetics, the phenotype-driven approach to investigating gene identity and function, has a long history in mouse genetics. Random mutations in the mouse transcend bias about gene function and provide avenues towards unique discoveries. The study of the peripheral nervous system is no exception; from historical strains such as the trembler mouse, which led to the identification of PMP22 as a human disease gene causing multiple forms of peripheral neuropathy, to the more recent identification of the claw paw and sprawling mutations, forward genetics has long been a tool for probing the physiology, pathogenesis, and genetics of the PNS. Even as spontaneous and mutagenized mice continue to enable the identification of novel genes, provide allelic series for detailed functional studies, and generate models useful for clinical research, new methods, such as the piggyBac transposon, are being developed to further harness the power of forward genetics. Special issue article in honor of Dr. George DeVries.     

Peripheral Nervous System Myelin and Schwann Cell Glycoproteins: Identification by Lectin Binding and Partial Purification of a Peripheral Nervous System Myelin-Specific 170,000 Molecular Weight Glycoprotein

Radioiodinated lectins were used to detect glycoproteins of peripheral nervous system (PNS) myelin (rat, human, bovine) and cultured rat Schwann cells. Proteins were resolved by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis and transferred to nitrocellulose filters. The filters were overlaid with radioiodinated lectins of known saccharide affinities. These included concanavalin A, Helix pomatia, Limulus polyphemus, Maclura pomifera, peanut, soybean, Ulex europaeus, and wheat germ agglutinins. Inclusion of the appropriate monosaccharide in the overlay solution (0.2 M) inhibited lectin binding to the nitrocellulose-fixed proteins. Fluorography permitted identification of 26 myelin glycoproteins and many more in Schwann cells. All lectins labeled a band present in myelin, but not Schwann cells, corresponding to the major PNS myelin protein, P0. Our attention focused on a high-molecular-weight myelin glycoprotein [apparent molecular weight (Mr) 170,000], which appeared abundant by Coomassie Blue staining and which was heavily labeled by all lectins except concanavalin A. A protein with approximately this Mr and lectin-binding pattern was present in human and bovine PNS myelin as well, but not detected in rat Schwann cells, CNS myelin, liver and fibroblast homogenates, or cultured bovine oligodendroglia. Hence this 170,000 Mr glycoprotein is apparently unique to PNS myelin.     

Development of Some Elements of the Peripheral Nervous System of the Locust Locusta migratoria during Larval Ontogenesis

Using supravital Methylene blue staining, development of elements of the peripheral nervous system was traced in the 1st–5th instar larvae of the locust Locusta migratoria L. Data were obtained on sensory cells of the I and II types in larvae of different instars, as well as on character of their changes in the course of larval development of the insect. The studied elements of the peripheral nervous system have been shown to be essentially transformed in the course of larval ontogenesis. The data are presented about the sensory cells of the proximal parts of the nerve trunks; they indicate that in the course of larvae development the cell number in these trunks near the ganglia of the nerve chain decreases, which might be due to their partial degeneration. With growth of muscle, changes in their sensory innervation take place. Subepithelial nerve plexus in larvae is largely represented in areas with hard and soft cuticles.     

Myelin-Associated Glycoprotein in the Central and Peripheral Nervous System of Quaking Mice

The myelin-associated glycoprotein (MAG) was quantitated in the CNS and PNS of quaking mice and the levels compared to the levels of myelin basic protein (MBP) and 2':3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity. In the brainstems of 36-day-old quaking mice, MBP, MAG, and CNPase were reduced to 12, 16, and 29% of control levels, respectively. In the sciatic nerves of the 36-day-old quaking mice, MBP and CNPase were 38 and 75% of control levels, respectively, whereas the concentration of MAG was unchanged or slightly increased. Similar quantitative results were obtained for the sciatic nerves and spinal roots of 7-month-old quaking mice. Immunoblots showed that the principal MAG band from the brainstems, sciatic nerves, and spinal roots of the quaking mice had a higher than normal apparent Mr. In addition, there was a minor component reacting with anti-MAG antiserum in the brainstems of the quaking mice that had a slightly lower Mr than control MAG and was not detected in the normal mice. The results for the quaking mice are compared with those from similar studies on other mutants with dysmyelination of the CNS and PNS.     

End-Structure of Afferent Axons Injured in the Peripheral and Central Nervous System

The end-structure of afferent axons chronically severed in the rat sciatic nerve or dorsal column (DC) was visualized by centrifugal transport of horseradish peroxidase (HRP) or wheatgerm agglutinin conjugated to HRP (WGA:HRP) injected into the L₄ or L₅ dorsal root ganglion. Nerve regeneration was prevented and neuroma formation encouraged by tightly ligating the cut nerve end. For the first few weeks postoperative, the time during which afferents trapped in a nerve-end neuroma generate their most intense ectopic impulse barrage, the developing neuroma was dominated by swollen terminal end-bulbs. There was some axonal dying-back, retrograde fiber growth, and terminal sprouting, but little preterminal branching. The rich tangle of fine preterminal branches usually thought of in relation to nerve-end neuromas did not elaborate until several months postoperative, a time when the neuroma is relatively quiescent electrically. Afferents cut in the DC, which never develop dramatic ectopic electrical activity, showed morphological peculiarities similar to nerve-end neuromas during the early postoperative period, including retrograde fiber growth and minimal sprouting. They did not, however, go on to form luxuriant branches. These data provide preliminary clues as to the structure of the ectopic impulse-generating mechanism thought to underlie paresthesias and pain associated with peripheral nerve injury.     

Integrated analysis of the conformation of a protein-linked spin label by crystallography,EPR and NMR spectroscopy

Long-range structural information derived from paramagnetic relaxation enhancement observed in the presence of a paramagnetic nitroxide radical is highly useful for structural characterization of globular, modular and intrinsically disordered proteins, as well as protein–protein and protein-DNA complexes. Here we characterized the conformation of a spin-label attached to the homodimeric protein CylR2 using a combination of X-ray crystallography, electron paramagnetic resonance (EPR) and NMR spectroscopy. Close agreement was found between the conformation of the spin label observed in the crystal structure with interspin distances measured by EPR and signal broadening in NMR spectra, suggesting that the conformation seen in the crystal structure is also preferred in solution. In contrast, conformations of the spin label observed in crystal structures of T4 lysozyme are not in agreement with the paramagnetic relaxation enhancement observed for spin-labeled CylR2 in solution. Our data demonstrate that accurate positioning of the paramagnetic center is essential for high-resolution structure determination.     

Evidence for the Association of 2',3'-Cyclic-Nucleotide 3'-Phosphodiesterase with Myelin-Related Membranes in Peripheral Nervous System

Abstract: In PNS, the specific activity of 2′,3′-cyclic nucleotide 3′-phospho–diesterase (CNP) in myelin was not enriched over the starting homogenate. Nevertheless, most of the total activity was recovered in myelin. In myelin-deficient mutants, low CNP activities were measured in sciatic nerves. CNP specific activities were similar in myelinated and non-myelinated nerves but in non-nervous tissues, they were significantly lower than in nervous tissue. There was no indication for the presence of an isoenzyme of CNP in peripheral nerves. These results indicate that CNP is present in PNS myelin and preferentially localized in Schwann cell plasma membranes.     

On the Fine Structure of the Nervous System of Tubiluchus philippinensis (Tubiluchidae,Priapulida)

At the mouth tube/introvert border a circumenteric intraepithelial nerve ring occupies a circular ridge protruding into the body cavity. The ring has a centrally located neuropile nearly free of perikarya and two zones of different perikarya above and below the neuropile. Presumably non-neuronal perikarya have an oval nucleus, large heterochromatin clumps and marked filament bundles. Such elements resemble tanycytic glial cells. Two types of presumably neuronal perikarya contain small cytoplasmic granules, similar to those in nerve fibre profiles. One of these neurons has a pale nucleus with a prominent nucleolus, the other a rather inconspicuous nucleus similar to that of the tanycytic cells. The neuronal processes of the fibre ring differ in diameter and contain clear and dense core vesicles, small granules (high or medium electron density) or granules with a dense periphery and a light centre. Sometimes neighbouring processes seem interconnected by electrical synapses. Images suggesting chemical synapses are rare. A large intraepithelial nerve lies in the wall of the introvert and ventral body wall close to the musculature, possibly innervated by this nerve. Frontal of the anus lies an intraepithelial ganglion demonstrating again a central neuropile. two neuronal types and tanycytic elements with filament bundles. Comparative aspects of the characters of the Tubiluchus nervous system are also discussed.     

Alterations in Protective Enzymes Against Peroxidation in the Central and Peripheral Nervous System of Control and Dysmyelinating Mutant Mice

The activities of peroxide-detoxifying enzymes such as superoxide dismutase (SOD), glutathione peroxidase, glutathione reductase, and catalase were measured in the nervous system of neurological dysmyelinating mutants: quaking (Qk), shiverer (Shi), and trembler (Tr) mice. Cu/Zn-SOD activity was higher in the cerebellum of Qk and Shi mice (by 53% and 106%, respectively) in comparison with controls, but it was the same in the cerebellum of Tr mice and their corresponding controls. In contrast, there was no difference in the level of Cu/Zn-SOD activity in the cerebrum of Qk, Shi, and Tr mice and their respective controls. Mn-SOD activity was the same among all the mutants compared to control animals in both cerebrum and cerebellum. In Shi cerebellum, glutathione peroxidase and glutathione reductase activities were slightly decreased (a 21.6% and a 13.2% diminution, respectively), whereas catalase activity in cerebrum and cerebellum was the same among mutants and control mice. In the sciatic nerve from Tr mice, all the enzymatic activities were enhanced: sixfold increase for total SOD, and 2.4-fold, 3.5-fold, and 1.8-fold increase for glutathione peroxidase, glutathione reductase, and catalase, respectively.