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Notch controls embryonic Schwann cell differentiation, postnatal myelination and adult plasticity.

ABSTRACT: Notch signaling is central to vertebrate development, and analysis of Notch has provided important insights into pathogenetic mechanisms in the CNS and many other tissues. However, surprisingly little is known about the role of Notch in the development and pathology of Schwann cells and peripheral nerves. Using transgenic mice and cell cultures, we found that Notch has complex and extensive regulatory functions in Schwann cells. Notch promoted the generation of Schwann cells from Schwann cell precursors and regulated the size of the Schwann cell pool by controlling proliferation. Notch inhibited myelination, establishing that myelination is subject to negative transcriptional regulation that opposes forward drives such as Krox20. Notably, in the adult, Notch dysregulation resulted in demyelination; this finding identifies a signaling pathway that induces myelin breakdown in vivo. These findings are relevant for understanding the molecular mechanisms that control Schwann cell plasticity and underlie nerve pathology, including demyelinating neuropathies and tumorigenesis.

SUBMITTER: Woodhoo A

PROVIDER: S-EPMC2782951 | biostudies-literature | 2009 Jul

REPOSITORIES: biostudies-literature

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Notch controls embryonic Schwann cell differentiation, postnatal myelination and adult plasticity.

Woodhoo Ashwin A Alonso Maria B Duran MB Droggiti Anna A Turmaine Mark M D'Antonio Maurizio M Parkinson David B DB Wilton Daniel K DK Al-Shawi Raya R Simons Paul P Shen Jie J Guillemot Francois F Radtke Freddy F Meijer Dies D Feltri M Laura ML Wrabetz Lawrence L Mirsky Rhona R Jessen Kristján R KR

Nature neuroscience 20090614 7

Notch signaling is central to vertebrate development, and analysis of Notch has provided important insights into pathogenetic mechanisms in the CNS and many other tissues. However, surprisingly little is known about the role of Notch in the development and pathology of Schwann cells and peripheral nerves. Using transgenic mice and cell cultures, we found that Notch has complex and extensive regulatory functions in Schwann cells. Notch promoted the generation of Schwann cells from Schwann cell pr ...[more]

PMID: 19525946

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Project description:BackgroundAxonal myelination is critical for the functioning of vertebrate nervous system. Myelin sheath malformation or degeneration can cause a variety of neurological diseases. Our previous study identified multiple potential myelination-related transcriptional factors (TFs), including expressed sequence tag (ETS) variant transcription factor 1 (Etv1)/Er81, via gene microarray analysis of Schwann cells (SCs) at various myelination stages. Etv1 is known to be involved in the regulation of neuronal specialization, muscle spindle differentiation, and sensorimotor connectivity. However, to our knowledge, to date, there are no relevant studies that Etv1 regulates SC myelination.MethodsTo investigate the roles of Etv1 in SC re-myelination, an in vivo mouse myelination model was used, in which the sciatic nerve is crushed. Etv1 in nerves was knocked down via in situ injection of cholesterol-modified Etv1-small interfering (si)RNA. The expression of myelin-associated glycoprotein (MAG) was evaluated by Western blotting (WB) and immunohistochemistry (IHC). Myelination was assessed by transmission electron microscopy (TEM). The effects of Etv1 on SC proliferation, migration, and differentiation were assessed in vitro using the EdU cell proliferation kit, a culture-insert scratch assay, a SC aggregate sphere migration assay on the axons of dorsal root ganglions (DRGs), and a SC differentiation model. Chromatin immunoprecipitation (ChIP) united with quantitative real-time PCR (qPCR), known as ChIP-qPCR, and luciferase activity reporter assays were performed to explore the possible mechanisms by which Etv1 controls SC differentiation and myelination.ResultsThe results demonstrated that Etv1 promoted myelination by facilitating SC proliferation, migration, and differentiation. Etv1 expression in SCs was upregulated during re-myelination, and knocking down Etv1 expression dramatically abrogated SC re-myelination in the crushed sciatic nerves. Moreover, silencing of Etv1 by siRNA in SCs in vitro inhibited its migration, proliferation, and differentiation. The results of ChIP-qPCR and luciferase reporter assay showed that Etv1 may regulate SC differentiation and myelination by binding to the promoters of myelination-related genes, such as MAG and Runx2, to initiate their transcription.ConclusionsTaken together, these findings demonstrated a previously unknown role of Etv1 in SC differentiation and myelination, providing a candidate molecular target for clinical interventions in demyelinating diseases.

Project description:Isolated Schwann cells (SCs) respond to cAMP elevation by adopting a differentiated post-mitotic state that exhibits high levels of Krox-20, a transcriptional enhancer of myelination, and mature SC markers such as the myelin lipid galactocerebroside (O1). To address how cAMP controls myelination, we performed a series of cell culture experiments which compared the differentiating responses of isolated and axon-related SCs to cAMP analogs and ascorbate, a known inducer of axon ensheathment, basal lamina formation and myelination. In axon-related SCs, cAMP induced the expression of Krox-20 and O1 without a concomitant increase in the expression of myelin basic protein (MBP) and without promoting axon ensheathment, collagen synthesis or basal lamina assembly. When cAMP was provided together with ascorbate, a dramatic enhancement of MBP expression occurred, indicating that cAMP primes SCs to form myelin only under conditions supportive of basal lamina formation. Experiments using a combination of cell permeable cAMP analogs and type-selective adenylyl cyclase (AC) agonists and antagonists revealed that selective transmembrane AC (tmAC) activation with forskolin was not sufficient for full SC differentiation and that the attainment of an O1 positive state also relied on the activity of the soluble AC (sAC), a bicarbonate sensor that is insensitive to forskolin and GPCR activation. Pharmacological and immunological evidence indicated that SCs expressed sAC and that sAC activity was required for morphological differentiation and the expression of myelin markers such as O1 and protein zero. To conclude, our data indicates that cAMP did not directly drive myelination but rather the transition into an O1 positive state, which is perhaps the most critical cAMP-dependent rate limiting step for the onset of myelination. The temporally restricted role of cAMP in inducing differentiation independently of basal lamina formation provides a clear example of the uncoupling of signals controlling differentiation and myelination in SCs.

Dataset Information

Notch controls embryonic Schwann cell differentiation, postnatal myelination and adult plasticity.

Publications

Notch controls embryonic Schwann cell differentiation, postnatal myelination and adult plasticity.

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