Schwann cells myelination

Siglec-4b SMP (Schwann cell myelin protein) Schwann cells in quail Neu5Ac-a(2-3)-Gal-... 

In order to elucidate the extended glycoconjugate binding specifities of MAG and other siglecs (Schwann cell myelin protein [SMP] and sialoadhesin [Sn]), Schnaar et al. [26a,27b] measured the siglec-mediated half-maximal cell adhesion to several immobilized natural and synthetically modified gangliosides (Table 16.2) [29]. 

Noebe/s I think the latter is correct, because myelin basic protein is actually present in oligodendrocytes centrally and Schwann cells peripherally. But in the shiverer mouse, Schwann cell myelination of peripheral nerves is relatively unaffected by the same genetic lesion that prevents formation of the central white matter. The protein must either play a different role in those two cell types, or they signal to axons in different ways. Whether it is there or not, if you irritate a ghal ceh, the oligodendrocyte will say one thing to a central axon and the Schwann cells may say something different to a peripheral axon. 

Fernandezvalle, C., Gwynn, L., Wood, P.M., Carbonetto, S. and Bunge, M.B. (1994) Anti-beta-1 integrin antibody inhibits Schwann cell myelination, J. Neurobiol. 25 1207-1226. 

Dupin, E., Baroffio, A., Dulac, C., Cameron-Curry, P. and Le Douarin, N.M. (1990) Schwann-cell differentiation in clonal cultures of the neural crest as evidenced by the anti-schwann cell myelin protein monoclonal antibody. Proc. Natl. Acad. Sci USA 87 1119-1123. 

Dulac, C., Tropak, M. B., Cameron-Curry, P, Rossier, J., Marshak, D. R., Roder, J., and Le Douarin, N. M. (1992) Molecular characterization of the Schwann cell myelin protein, SMP structural similarities within the immunoglobulin super-family. Neuron 8, 323-334. 

Collins BE, Kiso M, Hasegawa A, Tropak MB, Roder JC, et al. Binding specificities of the sialoadhesin family of I-type lectins. Sialic acid linkage and substructure requirements for binding of myelin-associated glycoprotein, Schwann cell myelin protein, and sialoadhesin. J. Biol Chem. 1997 272 16889-16895. 

When large areas of the membrane are depolarized in this manner, the electrochemical disturbance propagates in wave-like form down the membrane, generating a nerve impulse. Myelin sheets, formed by Schwann cells, wrap around nerve fibers and provide an electrical insulator that surrounds most of the nerve and greatly speeds up the propagation of the wave (signal) by allowing ions to flow in and out of the membrane... 

In the periphery PROG and PREG may well have an important trophic action since their production in Schwann cells has been shown to result in increased myelin synthesis in regenerating rat sciatic nerve and cultured dorsal root ganglia (see Koenig et al. 1995). 

Koenig, HE, Schumacher, M, Ferzaz, B, DeThi, A, Ressouches, A, Gennoun, R, Jung-Tester, L, Robel, P, Akwa, Y and Baulieu, EE (1995) Progesterone S5mthesis and myelin formation by Schwann cells. Science 286 1500-1503. 

The afferent fibres differ in their conduction velocity and degree of myelination, and can be distinguished by their diameter. The large diameter A S-fibres are myelinated by Schwann cells and hence have a fast conduction velocity. This group of nerve fibres innervates receptors in the dermis and is involved in the transmission of low-threshold, non-noxious information, such as touch. The A5-fibre is less densely myelinated and conveys both non-noxious and noxious sensory information. The unmyelinated C-fibre conveys high-threshold noxious inputs and has the slowest conduction velocity of all three fibre types. 

Myelin A segmented laminated lipoprotein sheath formed by glial cells (oligodendrocytes and Schwann cells). It is wrapped round the axon and acts as a biological insulating material. 

The Schwann cell is the myelin-producing cell of the peripheral nervous system 16... 

The axon emerges from a neuron as a slender thread and frequently does not branch until it nears its target. In contrast to the dendrite and the soma, the axon is myelinated frequently, thus increasing its efficiency as a conducting unit. Myelin, a spirally wrapped membrane (see Ch. 4), is laid down in segments, or internodes, by oligodendrocytes in the CNS and by Schwann cells in the PNS. The naked regions of axon between adjacent myelin internodes are known as nodes of Ranvier (see below). 

Myelinating oligodendrocytes have been studied extensively [5,30] (see Ch. 4). Examination of the CNS during myelinogenesis (Fig. 1-15) reveals connections between the cell body and the myelin sheath [31] however, connections between these elements have never been demonstrated in a normal adult animal, unlike the PNS counterpart, the Schwann cell. In contrast to the Schwann cell (see below), the oligodendrocyte is capable of producing many internodes of myelin simultaneously. It has been estimated that oligodendrocytes in the optic nerve produce... 

The Schwann cell is the myelin-producing cell of the peripheral nervous system. When axons leave the CNS, they lose their neuroglial interrelationships and traverse a short transitional zone where they are invested by an astroglial sheath enclosed in the basal lamina of the glia limitans. The basal lamina then becomes continuous with... 

FIGURE 1-19 A myelinated PNS axon (A) is surrounded by a Schwann cell nucleus (N). Note the fuzzy basal lamina around the cell, the rich cytoplasm, the inner and outer mesaxons (arrows), the close proximity of the cell to its myelin sheath and the 1 1 (celhmyelin internode) relationship. A process of an endoneurial cell is seen (lower left), and unstained collagen (c) lies in the endoneurial space (white dots). X20,000. 

FIGURE 4-4 Electron micrograph of a single peripheral nerve fiber from rabbit. Note that the myelin sheath has a lamellated structure and is surrounded by Schwann cell cytoplasm. The outer mesaxon (arrowhead) can be seen in lower left. AX, axon. (Courtesy of Dr Cedric Raine.)... 

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