Matthias Weider

Gain of Olig2 function in oligodendrocyte progenitors promotes remyelination.

The basic helix-loop-helix transcription factor Olig2 is a key determinant for the specification of neural precursor cells into oligodendrocyte progenitor cells. However, the functional role of Olig2 in oligodendrocyte migration and differentiation remains elusive both during developmental myelination and under demyelinating conditions of the adult central nervous system. To decipher Olig2 functions, we generated transgenic mice (TetOlig2:Sox10(rtTA/+)) overexpressing Olig2 in Sox10(+) oligodendroglial cells in a doxycycline inducible manner. We show that Olig2 overexpression increases the generation of differentiated oligodendrocytes, leading to precocious myelination of the central nervous system. Unexpectedly, we found that gain of Olig2 function in oligodendrocyte progenitor cells enhances their migration rate. To determine whether Olig2 overexpression in adult oligodendrocyte progenitor cells promotes oligodendrocyte regeneration for myelin repair, we induced lysophosphatidylcholine demyelination in the corpus callosum of TetOlig2:Sox10(rtTA/+) and control mice. We found that Olig2 overexpression enhanced oligodendrocyte progenitor cell differentiation and remyelination. To assess the relevance of these findings in demyelinating diseases, we also examined OLIG2 expression in multiple sclerosis lesions. We demonstrate that OLIG2 displays a differential expression pattern in multiple sclerosis lesions that correlates with lesion activity. Strikingly, OLIG2 was predominantly detected in NOGO-A(+) (now known as RTN4-A) maturing oligodendrocytes, which prevailed in active lesion borders, rather than chronic silent and shadow plaques. Taken together, our data provide proof of principle indicating that OLIG2 overexpression in oligodendrocyte progenitor cells might be a possible therapeutic mechanism for enhancing myelin repair.

Brg1-Dependent Chromatin Remodelling Is Not Essentially Required during Oligodendroglial Differentiation

Myelinating Schwann cells in the vertebrate peripheral nervous system rely on Brg1 (Smarca4) for terminal differentiation. Brg1 serves as central ATP-hydrolyzing subunit of the chromatin remodelling BAF complexes and is recruited during myelination as part of these complexes by the transcription factor Sox10 in Schwann cells. Here, we analyzed the role of Brg1 during development of myelinating oligodendrocytes in the CNS of the mouse. Following Brg1 deletion in oligodendrocyte precursors, these cells showed normal survival, proliferation, and migration. A mild but significant reduction in the number of oligodendrocytes with myelin gene expression in the absence of Brg1 points to a contribution to oligodendroglial differentiation but also shows that the role of Brg1 is much less prominent than during Schwann cell differentiation. Additionally, we failed to obtain evidence for a genetic interaction between Brg1 and Sox10 comparable with the one in Schwann cells. This argues that similarities exist between the regulatory networks and mechanisms in both types of myelinating glia but that the exact mode of action and the relevance of functional interactions differ, pointing to a surprising degree of variability in the control of myelination.

SoxE factors: Transcriptional regulators of neural differentiation and nervous system development

Sox8, Sox9 and Sox10 represent the three vertebrate members of the SoxE subclass of high-mobility-group domain containing Sox transcription factors. They play important roles in the peripheral and central nervous systems as regulators of stemness, specification, survival, lineage progression, glial differentiation and homeostasis. Functions are frequently overlapping, but sometimes antagonistic. SoxE proteins dynamically interact with transcriptional regulators, chromatin changing complexes and components of the transcriptional machinery. By establishing regulatory circuits with other transcription factors and microRNAs, SoxE proteins perform divergent functions in several cell lineages of the vertebrate nervous system, and at different developmental stages in the same cell lineage. The underlying molecular mechanisms are the topic of this review.

Elevated In Vivo Levels of a Single Transcription Factor Directly Convert Satellite Glia into Oligodendrocyte-like Cells

Oligodendrocytes are the myelinating glia of the central nervous system and ensure rapid saltatory conduction. Shortage or loss of these cells leads to severe malfunctions as observed in human leukodystrophies and multiple sclerosis, and their replenishment by reprogramming or cell conversion strategies is an important research aim. Using a transgenic approach we increased levels of the transcription factor Sox10 throughout the mouse embryo and thereby prompted Fabp7-positive glial cells in dorsal root ganglia of the peripheral nervous system to convert into cells with oligodendrocyte characteristics including myelin gene expression. These rarely studied and poorly characterized satellite glia did not go through a classic oligodendrocyte precursor cell stage. Instead, Sox10 directly induced key elements of the regulatory network of differentiating oligodendrocytes, including Olig2, Olig1, Nkx2.2 and Myrf. An upstream enhancer mediated the direct induction of the Olig2 gene. Unlike Sox10, Olig2 was not capable of generating oligodendrocyte-like cells in dorsal root ganglia. Our findings provide proof-of-concept that Sox10 can convert conducive cells into oligodendrocyte-like cells in vivo and delineates options for future therapeutic strategies.

Sox appeal - Sox10 attracts epigenetic and transcriptional regulators in myelinating glia.

Abstract Sox10 belongs to the Sox family of high-mobility group-box transcription factors. It fulfils widespread and essential functions in myelinating glia at multiple stages of development such as glial specification, survival and terminal differentiation. To a large extent, these diverse activities can be attributed to its capacity to interact with different transcription factors in distinct regulatory networks. Beyond transcription factors, an increasing number of interaction partners are emerging with alternative impact on gene expression. These include components of the mediator complex, the Brahma-associated factor complex and histone deacetylases. Here, we discuss interactions with functional relevance in myelinating glia and link Sox10 function in these cells not only to gene transcription, but also to epigenetics and chromatin remodeling.

Desert Hedgehog Links Transcription Factor Sox10 to Perineurial Development

Schwann cells are the main glial cell type in the PNS. They develop along nerves during embryogenesis and rely on the HMG domain containing Sox10 transcription factor for specification, lineage progression, and terminal differentiation. Sox10 deletion in immature Schwann cells caused peripheral nerve defects in mice that were not restricted to this glial cell type, although expression in the nerve and gene loss were. Formation of the perineurium as the protecting sheath was, for instance, heavily compromised. This resembled the defect observed after loss of Desert hedgehog (Dhh) in mice. Here we show that Sox10 activates Dhh expression in Schwann cells via an enhancer that is located in intron 1 of the Dhh gene. Sox10 binds this enhancer in monomeric form via several sites. Mutation of these sites abolishes both Schwann-cell-specific activity and Sox10 responsiveness in vitro and in transgenic mouse embryos. This argues that Sox10 activates Dhh expression by direct binding to the enhancer and by increasing Dhh levels promotes formation of the perineurial sheath. This represents the first mechanism for a non-cell-autonomous function of Sox10 during peripheral nerve development.

The Dual‐specificity phosphatase Dusp15 is regulated by Sox10 and Myrf in Myelinating Oligodendrocytes

Differentiation of oligodendrocytes and myelin production in the vertebrate central nervous system require highly concerted changes in gene expression. The transcription factors Sox10 and Myrf are both central to this process and jointly regulate expression of myelin genes. Here we show that Sox10 and Myrf also cooperate in the activation of the gene coding for the dual specificity protein phosphatase Dusp15 (also known as VHY) during this process. Activation is mediated by the Dusp15 promoter, which is also sufficient to drive oligodendroglial gene expression in vivo. It contains both a functional Sox10 and a functional Myrf binding site. Whereas Sox10 binds as a monomer, Myrf binds as a trimer. Available data furthermore indicate that cooperative activation is not a function of facilitated binding, but occurs at a later step of the activation process. shRNA‐mediated knockdown of Dusp15 reduced expression of early and late differentiation markers in CG4 and primary oligodendroglial cells, whereas Dusp15 overexpression increased it transiently. This argues that Dusp15 is not only a joint target of Sox10 and Myrf in oligodendrocytes but may also mediate some of their effects during oligodendrocyte differentiation and myelin formation. GLIA 2016;64:2120–2132

BRG1 interacts with SOX10 to establish the melanocyte lineage and to promote differentiation

Abstract Mutations in SOX10 cause neurocristopathies which display varying degrees of hypopigmentation. Using a sensitized mutagenesis screen, we identified Smarca4 as a modifier gene that exacerbates the phenotypic severity of Sox10 haplo-insufficient mice. Conditional deletion of Smarca4 in SOX10 expressing cells resulted in reduced numbers of cranial and ventral trunk melanoblasts. To define the requirement for the Smarca4 -encoded BRG1 subunit of the SWI/SNF chromatin remodeling complex, we employed in vitro models of melanocyte differentiation in which induction of melanocyte-specific gene expression is closely linked to chromatin alterations. We found that BRG1 was required for expression of Dct, Tyrp1 and Tyr, genes that are regulated by SOX10 and MITF and for chromatin remodeling at distal and proximal regulatory sites. SOX10 was found to physically interact with BRG1 in differentiating melanocytes and binding of SOX10 to the Tyrp1 distal enhancer temporally coincided with recruitment of BRG1. Our data show that SOX10 cooperates with MITF to facilitate BRG1 binding to distal enhancers of melanocyte-specific genes. Thus, BRG1 is a SOX10 co-activator, required to establish the melanocyte lineage and promote expression of genes important for melanocyte function.

Transcription factor Sox10 regulates oligodendroglial Sox9 levels via microRNAs

During development of myelin‐forming oligodendrocytes in the central nervous system the two closely related transcription factors Sox9 and Sox10 play essential roles that are partly shared and partly unique. Whereas Sox9 primarily functions during oligodendroglial specification, Sox10 is uniquely required to induce terminal differentiation and myelination. During this process, Sox10 protein levels rise substantially. As this coincides with a reciprocal decrease in Sox9, we postulated that Sox10 influences Sox9 amounts in differentiating oligodendrocytes. Here we show that Sox9 levels are indeed inversely coupled to Sox10 levels such that Sox10 deletion in oligodendroglial cells evokes a reciprocal increase in Sox9. We furthermore provide evidence that this coupling involves upregulation of microRNAs miR335 and miR338 as direct transcriptional targets of Sox10. The two microRNAs in turn recognize the 3′‐UTR of Sox9 mRNA and may thereby reduce Sox9 protein levels posttranscriptionally in oligodendroglial cells. Such a mechanism may enable oligodendroglial cells to adapt the ratio of both related Sox proteins in a manner required for successful lineage progression and differentiation. Mathematical modeling furthermore shows that the identified regulatory circuit has the potential to convert a transient stimulus into an irreversible switch of cellular properties and may thus contribute to terminal differentiation of oligodendrocytes.

Dual specificity phosphatase 15 regulates Erk activation in Schwann cells

Schwann cells and oligodendrocytes are the myelinating cells of the peripheral and central nervous system, respectively. Despite having different myelin components and different transcription factors driving their terminal differentiation there are shared molecular mechanisms between the two. Sox10 is one common transcription factor required for several steps in development of myelinating glia. However, other factors are divergent as Schwann cells need the transcription factor early growth response 2/Krox20 and oligodendrocytes require Myrf. Likewise, some signaling pathways, like the Erk1/2 kinases, are necessary in both cell types for proper myelination. Nonetheless, the molecular mechanisms that control this shared signaling pathway in myelinating cells remain only partially characterized. The hypothesis of this study is that signaling pathways that are similarly regulated in both Schwann cells and oligodendrocytes play central roles in coordinating the differentiation of myelinating glia. To address this hypothesis, we have used genome‐wide binding data to identify a relatively small set of genes that are similarly regulated by Sox10 in myelinating glia. We chose one such gene encoding Dual specificity phosphatase 15 (Dusp15) for further analysis in Schwann cell signaling. RNA interference and gene deletion by genome editing in cultured RT4 and primary Schwann cells showed Dusp15 is necessary for full activation of Erk1/2 phosphorylation. In addition, we show that Dusp15 represses expression of several myelin genes, including myelin basic protein. The data shown here support a mechanism by which early growth response 2 activates myelin genes, but also induces a negative feedback loop through Dusp15 to limit over‐expression of myelin genes.