Multiple conserved regulatory elements with overlapping functions determine Sox10 expression in mouse embryogenesis.

Expression and function of the transcription factor Sox10 is predominant in neural crest cells, its derivatives and in oligodendrocytes. To understand how Sox10 expression is regulated during development, we analysed the potential of evolutionary conserved non-coding sequences in the Sox10 genomic region to function as enhancers. By linking these sequences to a beta-galactosidase marker gene under the control of a minimal promoter, five regulatory regions were identified that direct marker gene expression in transgenic mice to Sox10 expressing cell types and tissues in a defined temporal pattern. These possible enhancers of the Sox10 gene mediate Sox10 expression in the otic vesicle, in oligodendrocytes and in several neural crest derivatives including the developing peripheral nervous system and the adrenal gland. They furthermore exhibit overlapping activities and share binding sites for Sox, Lef/Tcf, Pax and AP2 transcription factors. This may explain high level and robustness of Sox10 expression during embryonic development.

SoxD proteins influence multiple stages of oligodendrocyte development and modulate SoxE protein function.

The myelin-forming oligodendrocytes are an excellent model to study transcriptional regulation of specification events, lineage progression, and terminal differentiation in the central nervous system. Here, we show that the group D Sox transcription factors Sox5 and Sox6 jointly and cell-autonomously regulate several stages of oligodendrocyte development in the mouse spinal cord. They repress specification and terminal differentiation and influence migration patterns. As a consequence, oligodendrocyte precursors and terminally differentiating oligodendrocytes appear precociously in spinal cords deficient for both Sox proteins. Sox5 and Sox6 have opposite functions than the group E Sox proteins Sox9 and Sox10, which promote oligodendrocyte specification and terminal differentiation. Both genetic as well as molecular evidence suggests that Sox5 and Sox6 directly interfere with the function of group E Sox proteins. Our studies reveal a complex regulatory network between different groups of Sox proteins that is essential for proper progression of oligodendrocyte development.

Expression of connexin47 in oligodendrocytes is regulated by the Sox10 transcription factor.

In the central nervous system, Connexin32 and Connexin47 are confined to oligodendrocytes where they contribute to myelin formation and maintenance, and are essential for establishing a functional glial syncytium that ensures ionic homeostasis. Despite their importance, not much is known about the regulation of connexin gene expression in oligodendrocytes. Here, we identify group E Sox proteins, in particular Sox10, as essential transcriptional regulators of both connexins. Not only was expression of Connexin32 and Connexin47 severely compromised in spinal cords of mouse mutants with reduced amounts of group E Sox proteins. Sox10 also stimulated in transient transfections the Connexin32 promoter as well as Connexin47 promoter 1b which is the main Connexin47 promoter active in the postnatal spinal cord. Detailed characterization of Connexin47 promoter 1b identified a single monomer binding site that mediated Sox10-dependent promoter activation. The region containing this binding site was also occupied by endogenous Sox10 in 33B oligodendroglioma cells. These results add Connexin47 and Connexin32 to the list of Sox10 target genes and argue that Sox10 may influence transcription of many terminal differentiation and myelination genes in oligodendrocytes as an essential regulatory component of the myelination program.

The high-mobility group transcription factor Sox10 interacts with the N-myc-interacting protein Nmi.

The high-mobility group transcription factor Sox10 exerts many different roles during development of the neural crest and nervous system. To unravel its complex transcriptional functions, we have started to look for interaction partners. Here, we identify an association of Sox10 with the N-myc interactor Nmi, which was mediated by the high-mobility group of Sox10 and the central region of Nmi. In vivo relevance of this interaction is indicated by the fact that both proteins were co-expressed in glial cells, gliomas and in the spinal cord. Additionally, subcellular localization of Nmi in C6 glioma depended on the presence of Sox10 such that nuclear Nmi was more frequent in Sox10-expressing cells. Importantly, Nmi modulated the transcriptional activity of Sox10 in reporter gene assays. Nmi effects varied between different Sox10 target gene promoters, indicating that Nmi function in vivo may be promoter-specific.

Tumour necrosis factor alpha decreases glucose-6-phosphatase gene expression by activation of nuclear factor kappaB.

The key insulin-regulated gluconeogenic enzyme G6Pase (glucose-6-phosphatase) has an important function in the control of hepatic glucose production. Here we examined the inhibition of G6Pase gene transcription by TNF (tumour necrosis factor) in H4IIE hepatoma cells. TNF decreased dexamethasone/dibtuyryl cAMP-induced G6Pase mRNA levels. TNFalpha, but not insulin, led to rapid activation of NFkappaB (nuclear factor kappaB). The adenoviral overexpression of a dominant negative mutant of IkappaBalpha (inhibitor of NFkappaB alpha) prevented the suppression of G6Pase expression by TNFalpha, but did not affect that by insulin. The regulation of G6Pase by TNF was not mediated by activation of the phosphoinositide 3-kinase/protein kinase B pathway, extracellular-signal-regulated protein kinase or p38 mitogen-activated protein kinase. Reporter gene assays demonstrated a concentration-dependent down-regulation of G6Pase promoter activity by the transient overexpression of NFkappaB. Although two binding sites for NFkappaB were identified within the G6Pase promoter, neither of these sites, nor the insulin response unit or binding sites for Sp proteins, was necessary for the regulation of G6Pase promoter activity by TNFalpha. In conclusion, the data indicate that the activation of NFkappaB is sufficient to suppress G6Pase gene expression, and is required for the regulation by TNFalpha, but not by insulin. We propose that NFkappaB does not act by binding directly to the G6Pase promoter.