Untersuchungen zur microRNA-204-211-Familie in der oligodendroglialen Entwicklung

Die Myelinisierung von Axonen des Nervensystems ist von entscheidender Bedeutung für die rasche neuronale Signalweiterleitung. Die Ausbildung des Myelins sowie das Umwickeln der Axone werden im zentralen Nervensystem durch Oligodendrozyten vollzogen. In diesen stellen Transkriptionsfaktoren der Sox-Protein Familie unentbehrliche Regulatoren einer Vielzahl an Entwicklungs-Prozessen dar, wobei Sox10 während der Oligodendrogenese von großer Wichtigkeit ist. Unlängst wurde das Spektrum der nachweislich durch Sox10 induzierten Gene um microRNAs erweitert. In dieser Arbeit wurde die aktivierende Rolle von Sox10 auf Mitglieder der microRNA-204-211-Familie und deren Bedeutung in der Formierung differenzierter Oligodendrozyten untersucht. Aus der Analyse genregulatorischer Regionen der microRNA-204 und microRNA-211 ging hervor, dass Sox10 über deren Bindung die Transkription dieser microRNA-Familie in Reportergen Aktivitätstests induzieren kann. Gelretardierungsexperimente zeigten weiterhin die physische Interaktion von Sox10 mit den regulatorischen Elementen der microRNA-204. Überexpressions-Versuche für microRNA-204 in primären Ratten-Oligodendroglia gefolgt von immunozytochemischen Färbungen gegen Proliferations-Marker ließen auf die negative Regulation des Wachstums der Oligodendrozyten-Vorläuferzellen-Population durch microRNA-204 schließen. Proliferations-hemmende Effekte wurden darauffolgend durch Reportergen-Aktivitätstests und in vitro knockdown in Teilen der microRNA 204 vermittelten Inhibition von Ccnd2, einem positiven Regulator des Zellzyklus, zugeschrieben. Einhergehend mit der Reduktion der Proliferation wurde eine Zunahme der oligodendroglialen Differenzierung nach microRNA-204-Überexpression nachgewiesen. Die hierin beobachtete vermehrte Expression von Differenzierungsmarkern in primärer Zellkultur wurde auf die Hemmung der Translation von Sox4, einem negativen Regulator der Reifung von Oligodendrozyten, zurückgeführt. Zusammengefasst argumentieren diese Ergebnisse für einen Regulierungsmechanismus in dem microRNA-204 von Sox10 aktiviert wird und daraufhin den Austritt oligodendroglialer Vorläufer aus dem Zellzyklus und die Einleitung der terminalen Differenzierung unterstützt.Myelination of axons of the nervous system is decisive for rapid transduction of neuronal signals. In the central nervous system, formation of myelin and consequent wrapping of axons is accomplished by oligodendrocytes. Transcription factors of the Sox protein family are pivotal regulators of oligodendroglial development. Especially Sox10 is of crucial importance for proper oligodendrogenesis. Recently, the range of Sox10 induced genes has been extended to microRNAs. In this thesis, the activating role of Sox10 on members of the microRNA-204-211 family has been examined as well as the role of these microRNAs in the formation of differentiated oligodendrocytes. The analysis of microRNA-204 and microRNA-211 gene regulatory regions in reporter-gene assays demonstrated transcriptional activation of this microRNA family by Sox10. Electrophoretic-mobility-shift assays further displayed physical interaction of Sox10 with regulatory elements of microRNA 204. Overexpression of microRNA-204 in primary rat oligodendroglia followed by immunocytochemical stainings against proliferation markers suggest negative regulation of proliferation by microRNA-204. By reporter-gene assays and comparing effects of Ccnd2-knockdown and microRNA-204 overexpression, anti-proliferative effects were at least in part attributed to the inhibition of pro-proliferative Ccnd2 in vitro. Concomitant with reduced proliferation, an increase in the expression of maturation markers was observed. The elevated differentiation rate in primary cells by microRNA-204 could be explained by translational inhibition of Sox4, a repressor of oligodendrocyte maturation. These results argue for the existence of a regulatory circuit in which Sox10 activates microRNA-204 that in turn induces cell-cycle exit and initiates terminal differentiation

Crazy Little Thing Called Sox—New Insights in Oligodendroglial Sox Protein Function

In the central nervous system, oligodendrocytes wrap axons with myelin sheaths, which is essential for rapid transfer of electric signals and their trophic support. In oligodendroglia, transcription factors of the Sox protein family are pivotal regulators of a variety of developmental processes. These include specification, proliferation, and migration of oligodendrocyte precursor cells as well as terminal differentiation to mature myelinating oligodendrocytes. Sox proteins are further affected in demyelinating diseases and are involved in remyelination following damage of the central nervous system. Here we summarize and discuss latest findings on transcriptional regulation of Sox proteins, their function, target genes, and interaction with other transcription factors and chromatin remodelers in oligodendroglia with physiological and pathophysiological relevance

MicroRNA miR‐204 regulates proliferation and differentiation of oligodendroglia in culture

Oligodendrocytes wrap and physically shield axons of the central nervous system with myelin sheaths, resulting in rapid signal transduction and accurate neuronal function. The complex oligodendroglial development from immature oligodendrocyte precursor cells (OPCs) to myelinating oligodendrocytes (OLs) is profoundly dependent on the activity of transcription factors of the Sox protein family. Target genes of the crucial regulator Sox10 have recently been expanded to microRNAs. Here, we report miR‐204 as a novel transcriptional target of Sox10. Regulatory regions of miR‐204 show responsiveness to and binding of Sox10 in reporter gene assays and electromobility shift assays. Once expressed, miR‐204 inhibits OPC proliferation and facilitates differentiation into OLs in the presence of Sox10 as evident from overexpression in primary rat and mouse oligodendroglial cultures. Phenotypes are at least in part caused by miR‐204‐dependent repression of the pro‐proliferative Ccnd2 and the differentiation inhibiting Sox4. These findings argue that the transcriptional activator Sox10 forces oligodendroglial cells to exit the cell cycle and start differentiation by gene inhibition via miR‐204 induction

PEM fuel cells for the power supply of electronic appliances

At the Fraunhofer Institute for Solar Energy Systems ISE we develop customized fuel cell systems based on hydrogen or methanol as fuel. This article describes some scientific approaches for the basic understanding of fuel cells we are taking in terms of simulation (modeling) and characterization (data extraction). Furthermore, some systems which have been realized recently on the base of solid polymer electrolyte membrane (PEM) fuel cells, as well as the control scheme we developed for a completely autonomous mobile power box will be presented

PEM fuel cells for the power supply of electronic appliances

At the Fraunhofer Institute for Solar Energy Systems ISE we develop customized fuel cell systems based on hydrogen or methanol as fuel. This article describes some scientific approaches for the basic understanding of fuel cells we are taking in terms of simulation (modeling) and characterization (data extraction). Furthermore, some systems which have been realized recently on the base of solid polymer electrolyte membrane (PEM) fuel cells, as well as the control scheme we developed for a completely autonomous mobile power box will be presented