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Myosin II has distinct functions in PNS and CNS myelin sheath formation.

Wang H, Tewari A, Einheber S, Salzer JL, Melendez-Vasquez CV - J. Cell Biol. (2008)

Bottom Line: We have found that inhibition of myosin II, a key regulator of actin cytoskeleton dynamics, has remarkably opposite effects on myelin formation by Schwann cells (SC) and oligodendrocytes (OL).In contrast, OL branching, differentiation, and myelin formation are potentiated by inhibition of myosin II.Our data indicate that the mechanisms regulating myelination in the peripheral and central nervous systems are distinct.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, NY 10065, USA.

ABSTRACT
The myelin sheath forms by the spiral wrapping of a glial membrane around the axon. The mechanisms responsible for this process are unknown but are likely to involve coordinated changes in the glial cell cytoskeleton. We have found that inhibition of myosin II, a key regulator of actin cytoskeleton dynamics, has remarkably opposite effects on myelin formation by Schwann cells (SC) and oligodendrocytes (OL). Myosin II is necessary for initial interactions between SC and axons, and its inhibition or down-regulation impairs their ability to segregate axons and elongate along them, preventing the formation of a 1:1 relationship, which is critical for peripheral nervous system myelination. In contrast, OL branching, differentiation, and myelin formation are potentiated by inhibition of myosin II. Thus, by controlling the spatial and localized activation of actin polymerization, myosin II regulates SC polarization and OL branching, and by extension their ability to form myelin. Our data indicate that the mechanisms regulating myelination in the peripheral and central nervous systems are distinct.

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Knockdown of myosin II in OL-DRG cocultures enhances myelin formation. (A) 3-wk-old myelinating OL-DRG cocultures stained for MBP, Olig2, and neurofilament. Cocultures were infected with a lentiviral vector expressing shRNA against the regulatory chain of myosin II (shMLC) or nontargeting scrambled sequence (shSCR). Knockdown of MLC in OPC-DRG cocultures resulted in a significant increase in myelination similar to that observed in cultures treated with blebbistatin. Myelination in control cultures infected with vector alone or in cultures where neurons were preinfected with lentivirus was comparable to that observed in nontreated control culture (not depicted). Bars, 50 μm. (B) Quantitation of MBP+ segments per field. Data represent mean ± SEM from two independent experiments (three cultures per condition per experiment).
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fig5: Knockdown of myosin II in OL-DRG cocultures enhances myelin formation. (A) 3-wk-old myelinating OL-DRG cocultures stained for MBP, Olig2, and neurofilament. Cocultures were infected with a lentiviral vector expressing shRNA against the regulatory chain of myosin II (shMLC) or nontargeting scrambled sequence (shSCR). Knockdown of MLC in OPC-DRG cocultures resulted in a significant increase in myelination similar to that observed in cultures treated with blebbistatin. Myelination in control cultures infected with vector alone or in cultures where neurons were preinfected with lentivirus was comparable to that observed in nontreated control culture (not depicted). Bars, 50 μm. (B) Quantitation of MBP+ segments per field. Data represent mean ± SEM from two independent experiments (three cultures per condition per experiment).

Mentions: To further investigate the contribution of OL myosin II on myelin formation, we infected OPC-DRG cocultures with shRNA lentivirus against the regulatory chain of MLC. Lentiviral infection of purified OPC cultures resulted in significant cell death (unpublished data), whereas infection of OPC in cocultures with DRG neurons was well tolerated. Incubation of cocultures with lentivirus resulted in the preferential infection of OPC rather than neurons, as indicated by GFP expression (Fig. S3, available at http://www.jcb.org/cgi/content/full/jcb.200802091/DC1). As a further control, we infected established DRG cultures with the lentivirus for several days before adding OPC and inducing myelination. As shown in Fig. 5, knockdown of MLC in OPC-DRG cocultures also resulted in a significant increase (P < 0.001) in myelination similar to that observed in cultures treated with blebbistatin. Myelination in the presence of nontargeting lentivirus (shSCR) or vector alone was comparable to that observed in nontreated control cultures. In addition, myelination of neurons preinfected with lentivirus was comparable to controls (unpublished data), which further indicates that enhanced myelination results from the specific inhibition of myosin II in OL.


Myosin II has distinct functions in PNS and CNS myelin sheath formation.

Wang H, Tewari A, Einheber S, Salzer JL, Melendez-Vasquez CV - J. Cell Biol. (2008)

Knockdown of myosin II in OL-DRG cocultures enhances myelin formation. (A) 3-wk-old myelinating OL-DRG cocultures stained for MBP, Olig2, and neurofilament. Cocultures were infected with a lentiviral vector expressing shRNA against the regulatory chain of myosin II (shMLC) or nontargeting scrambled sequence (shSCR). Knockdown of MLC in OPC-DRG cocultures resulted in a significant increase in myelination similar to that observed in cultures treated with blebbistatin. Myelination in control cultures infected with vector alone or in cultures where neurons were preinfected with lentivirus was comparable to that observed in nontreated control culture (not depicted). Bars, 50 μm. (B) Quantitation of MBP+ segments per field. Data represent mean ± SEM from two independent experiments (three cultures per condition per experiment).
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Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2542477&req=5

fig5: Knockdown of myosin II in OL-DRG cocultures enhances myelin formation. (A) 3-wk-old myelinating OL-DRG cocultures stained for MBP, Olig2, and neurofilament. Cocultures were infected with a lentiviral vector expressing shRNA against the regulatory chain of myosin II (shMLC) or nontargeting scrambled sequence (shSCR). Knockdown of MLC in OPC-DRG cocultures resulted in a significant increase in myelination similar to that observed in cultures treated with blebbistatin. Myelination in control cultures infected with vector alone or in cultures where neurons were preinfected with lentivirus was comparable to that observed in nontreated control culture (not depicted). Bars, 50 μm. (B) Quantitation of MBP+ segments per field. Data represent mean ± SEM from two independent experiments (three cultures per condition per experiment).
Mentions: To further investigate the contribution of OL myosin II on myelin formation, we infected OPC-DRG cocultures with shRNA lentivirus against the regulatory chain of MLC. Lentiviral infection of purified OPC cultures resulted in significant cell death (unpublished data), whereas infection of OPC in cocultures with DRG neurons was well tolerated. Incubation of cocultures with lentivirus resulted in the preferential infection of OPC rather than neurons, as indicated by GFP expression (Fig. S3, available at http://www.jcb.org/cgi/content/full/jcb.200802091/DC1). As a further control, we infected established DRG cultures with the lentivirus for several days before adding OPC and inducing myelination. As shown in Fig. 5, knockdown of MLC in OPC-DRG cocultures also resulted in a significant increase (P < 0.001) in myelination similar to that observed in cultures treated with blebbistatin. Myelination in the presence of nontargeting lentivirus (shSCR) or vector alone was comparable to that observed in nontreated control cultures. In addition, myelination of neurons preinfected with lentivirus was comparable to controls (unpublished data), which further indicates that enhanced myelination results from the specific inhibition of myosin II in OL.

Bottom Line: We have found that inhibition of myosin II, a key regulator of actin cytoskeleton dynamics, has remarkably opposite effects on myelin formation by Schwann cells (SC) and oligodendrocytes (OL).In contrast, OL branching, differentiation, and myelin formation are potentiated by inhibition of myosin II.Our data indicate that the mechanisms regulating myelination in the peripheral and central nervous systems are distinct.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Hunter College, City University of New York, New York, NY 10065, USA.

ABSTRACT
The myelin sheath forms by the spiral wrapping of a glial membrane around the axon. The mechanisms responsible for this process are unknown but are likely to involve coordinated changes in the glial cell cytoskeleton. We have found that inhibition of myosin II, a key regulator of actin cytoskeleton dynamics, has remarkably opposite effects on myelin formation by Schwann cells (SC) and oligodendrocytes (OL). Myosin II is necessary for initial interactions between SC and axons, and its inhibition or down-regulation impairs their ability to segregate axons and elongate along them, preventing the formation of a 1:1 relationship, which is critical for peripheral nervous system myelination. In contrast, OL branching, differentiation, and myelin formation are potentiated by inhibition of myosin II. Thus, by controlling the spatial and localized activation of actin polymerization, myosin II regulates SC polarization and OL branching, and by extension their ability to form myelin. Our data indicate that the mechanisms regulating myelination in the peripheral and central nervous systems are distinct.

Show MeSH
Related in: MedlinePlus