Incisures of Schmidt-Lanterman

Understanding the dynamic axon-glial cell interaction underlying myelination is hampered by the lack of suitable imaging techniques. Here we demonstrate third harmonic generation microscopy (THGM) for label-free imaging of myelinating Schwann cells in live culture and ex vivo and in vivo tissue. A 3D structure was acquired for a variety of compact and noncompact myelin domains, including juxtaparanodes, Schmidt-Lanterman incisures, and Cajal bands. Other subcellular features of Schwann cells that escape traditional optical microscopies were also visualized. We tested THGM for morphometry of compact myelin. Unlike current methods based on electron microscopy, g-ratio could be determined along an extended length of myelinated fiber in the physiological condition. The precision of THGMbased g-ratio estimation was corroborated in mouse models of hypomyelination. Finally, we demonstrated the feasibility of THGM to monitor morphological changes of myelin during postnatal development and degeneration. The outstanding capabilities of THGM may be useful for elucidation of the mechanism of myelin formation and pathogenesis.myelin | Schwann cell | multiphoton microscopy | label-free imaging | morphometry M yelin is a multiple-layered membrane sheath surrounding the axon. In myelinated nerves, the conduction of action potentials is much faster and the speed depends strongly on the structure of myelin. The structural integrity must be therefore tightly regulated for proper conduction of neuronal impulses, but the underlying axon-glial cell interaction is not well understood. Since the days of Ramón y Cajal, light microscopy has been widely used to visualize myelin morphology (1). A variety of fluorescent probes specifically binding to myelin components have allowed studies of the interaction between molecules (2-4). However, most such labeling methods are not suitable for unraveling in vivo dynamics of myelination because cell membranes are compromised during staining (especially immunohistochemistry) and/or the procedures are prohibitively timeconsuming and invasive. It is thus of great interest to develop label-free methods. Recently, spectral confocal reflectance microscopy has been demonstrated for high-resolution in vivo imaging of myelin (5). There are also techniques of nonlinear optical microscopy, which are generally known to be more advantageous for imaging deep live tissue. Coherence anti-Stokes Raman scattering (CARS) microscopy, which requires two synchronized short pulse lasers for excitation, has been used for imaging in vivo myelin and detecting pathology (6, 7). Third harmonic generation (THG) microscopy is based on another nonlinear optical process of light emission, yielding distinguishable images from CARS. Though it has been demonstrated for imaging the white matter in the brain (8), so far few studies have applied THG microscopy (THGM) for elucidating the mechanism of myelin formation. Moreover, the omission of the peripheral nervous systems (PNS) in the previous studies is not trivial considering the s...

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“…3D). The classic funnel shape, familiar from previous electron and light microscopy (13,14), had an inclination angle of ∼10° (Fig. 3E).…”

Section: Significancementioning

confidence: 71%

“…Consider as an example the angle of SchmidtLanterman incisures. The noncompact domain has been depicted in an unrolled myelin sheath as obliquely traversing channels relative to the axon (14,29). This view suggests that the angle of incisures is related to the tilt of channel.…”

Section: Discussionmentioning

confidence: 99%

Label-free imaging of Schwann cell myelination by third harmonic generation microscopy

Lim¹,

Sharoukhov²,

Kassim

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…An additional and/or alternative possibility involves Cx29 and Cx32 localization at paranodal loops and Schmidt-Lanterman incisures, as seen in peripheral nerves (Li et al, 2002;Altevogt et al, 2002). Incisures have been observed in vivo in nerves of living animals , and electron microscopic studies of PNS have shown that they consist of short, circumferential dilations of Schwann cell cytoplasm spanning the full breath of myelin along internodal regions Friede and Samorajski, 1969;Ghabriel and Allt, 1981). Considering that myelin lamellae surrounding axons form impermeable barriers to diffusion of substances, Schmidt-Lanterman incisures may provide a route for metabolic support and maintenance of myelin sheaths (Webster, 1965;Williams and Hall, 1971a,b;Ghabriel and Allt, 1981).…”

Section: Connexins In Myelinmentioning

confidence: 99%

“…Incisures have been observed in vivo in nerves of living animals , and electron microscopic studies of PNS have shown that they consist of short, circumferential dilations of Schwann cell cytoplasm spanning the full breath of myelin along internodal regions Friede and Samorajski, 1969;Ghabriel and Allt, 1981). Considering that myelin lamellae surrounding axons form impermeable barriers to diffusion of substances, Schmidt-Lanterman incisures may provide a route for metabolic support and maintenance of myelin sheaths (Webster, 1965;Williams and Hall, 1971a,b;Ghabriel and Allt, 1981). It has also been proposed that connexins at incisures form autologous or reflexive gap junctions between successive inner to outer cytoplasmic membranes, thereby providing a pathway consisting of a series of gap junction channels for radial diffusion of ions and metabolites (Bergoffen et al, 1993;Scherer et al, 1995;Scherer, 1996;Bone et al, 1997;Balice-Gordon et al, 1998;Arroyo and Scherer, 2000).…”

Section: Connexins In Myelinmentioning

confidence: 99%

Connexin29 and connexin32 at oligodendrocyte and astrocyte gap junctions and in myelin of the mouse central nervous system

Nagy

Ionescu

Lynn

et al. 2003

J of Comparative Neurology

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The cellular localization, relation to other glial connexins (Cx30, Cx32, and Cx43), and developmental expression of Cx29 were investigated in the mouse central nervous system (CNS) with an anti-Cx29 antibody. Cx29 was enriched in subcellular fractions of myelin, and immunofluorescence for Cx29 was localized to oligodendrocytes and myelinated fibers throughout the brain and spinal cord. Oligodendrocyte somata displayed minute Cx29-immunopositive puncta around their periphery and intracellularly. In developing brain, Cx29 levels increased during the first few postnatal weeks and were highest in the adult brain. Immunofluorescence labeling for Cx29 in oligodendrocyte somata was intense at young ages and was dramatically shifted in localization primarily to myelinated fibers in mature CNS. Labeling for Cx32 also was localized to oligodendrocyte somata and myelin and absent in Cx32 knockout mice. Cx29 and Cx32 were minimally colocalized on oligodendrocytes somata and partly colocalized along myelinated fibers. At gap junctions on oligodendrocyte somata, Cx43/Cx32 and Cx30/Cx32 were strongly associated, but there was minimal association of Cx29 and Cx43. Cx32 was very sparsely associated with astrocytic connexins along myelinated fibers. With Cx26, Cx30, and Cx43 expressed in astrocytes and Cx29, Cx32, and Cx47 expressed in oligodendrocytes, the number of connexins localized to gap junctions of glial cells is increased to six. The results suggested that Cx29 in mature CNS contributes minimally to gap junctional intercellular communication in oligodendrocyte cell bodies but rather is targeted to myelin, where it, with Cx32, may contribute to connexin-mediated communication between adjacent layers of uncompacted myelin. Indexing termsbrain; glia; antibodies; intercellular communication; confocal microscopy; Schmidt-Lanterman incisures Cells in the central nervous system (CNS) communicate directly via gap junctions at close appositions between plasma membranes, thereby providing channels for movement of ions and small molecules from cell to cell. It appears that virtually every neural cell type in the brain has the capacity for gap junctional intercellular communication (GJIC), and evidence for several levels of complexity in this process is beginning to emerge. Each cell type exhibits Mugnaini, 1986;Rash et al., 1997Rash et al., , 2000 Nagy et al., 2003a). In addition, vast numbers of gap junctions have been reported to connect not only astrocyte processes of different cells but also those of the same cell, resulting in extensive autocellular coupling formed by autologous or reflexive gap junctions (Wolburg and Rohlmann, 1995;Nagy and Rash, 2000). At least 10 members of the family of connexin proteins that form gap junctions in mammalian tissues are expressed in the CNS, and individual cells and gap junctions often contain two or more different connexins (Nagy et al., 1999;Severs, 1999;Nagy and Dermietzel, 2000;Nagy and Rash, 2000). It is now established that A/A junctions contain Cx26, Cx30, and Cx43, and th...

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“…These noncompacted regions of myelin include the Schmidt-Lanterman incisures, which are conical tube-like cytoplasmic structures that cross the compact myelin and connect the Schwann cell peripheral (abaxonal) cytoplasm to the periaxonal (adaxonal) cytoplasm. It is believed that incisures are important for transport of metabolic substances across the myelin sheath and for the metabolic maintenance and longitudinal growth of the sheath (for review, see Ghabriel and Allt, 1981;Arroyo and Scherer, 2000).…”

Section: Introductionmentioning

confidence: 99%

Adherens Junctions in Myelinating Schwann Cells Stabilize Schmidt-Lanterman Incisures via Recruitment of p120 Catenin to E-Cadherin

Tricaud

Perrin-Tricaud²,

Brusés³

et al. 2005

J. Neurosci.

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Schwann cell myelin contains highly compacted layers of membrane as well as noncompacted regions with a visible cytoplasm. One of these cytoplasmic compartments is the Schmidt-Lanterman incisure, which spirals through the compacted layers and is believed to help sustain the growth and function of compact myelin. Incisures contain adherens junctions (AJs), the key components of which are E-cadherin, its cytoplasmic partners called catenins, and F-actin. To explore in vivo the role of cadherin and catenins in incisures, E-cadherin mutant proteins that completely replace endogenous cadherin have been delivered to the cells using adenovirus. When the introduced cadherin lacked its extracellular domain, association of p120 catenin (p120ctn) with the cadherin did not occur, and incisures disappeared. Remarkably, the additional replacement of two phosphorylatable tyrosines by phenylalanine in the cytoplasmic tail of the mutant cadherin restored both p120ctn binding and incisure architecture, indicating that p120ctn recruitment is critical for incisures maintenance and might be regulated by phosphorylations. In addition, the ability of the p120ctn/cadherin complex to support incisures was blocked by mutation of the Rho GTPase regulatory region of the p120ctn, and downregulation of Rac1 activity at the junction reversed this inhibition. Because Rho GTPases regulate the state of the actin filaments, these findings suggest that one role of p120ctn in incisures is to organize the cytoskeleton at the AJ. Finally, developmental studies of Schwann cells demonstrated that p120ctn recruitment from the cytoplasm to the AJ occurs before the appearance of Rac1 GTPase and F-actin at the junction.

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Incisures of Schmidt-Lanterman

Cited by 57 publications

References 67 publications

Label-free imaging of Schwann cell myelination by third harmonic generation microscopy

Label-free imaging of Schwann cell myelination by third harmonic generation microscopy

Connexin29 and connexin32 at oligodendrocyte and astrocyte gap junctions and in myelin of the mouse central nervous system

Adherens Junctions in Myelinating Schwann Cells Stabilize Schmidt-Lanterman Incisures via Recruitment of p120 Catenin to E-Cadherin

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