Transcription factor YinYang 2 alters neuronal ou

Authors: Martin Klar Pascal Fenske Fanny Rezza Vega Christof Dame Anja U Bräuer

Publish Date: 2015/09/09

Volume: 362, Issue: 2, Pages: 453-460

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Abstract

The YinYang 2 YY2 protein is the most recently described member of the family of YY transcription factors Despite its high structural and functional homology with the wellcharacterized YY1 less is known about its role in biological processes In previous studies we have found differential yy2 mRNA expression levels in various cell types of the murine brain To investigate the functional implication of yy2 in neurons we have examined the influence of altered cellular yy2 concentrations during neuronal differentiation Our results indicate that both the up and downregulation of yy2 significantly impairs the outgrowth of the major neurite of primary hippocampal neurons and the numbers of neuronal processes in proximate extensions Moreover enhanced expression of wildtype yy2 results in increased cell death whereas elevated expression levels of a yy2 DNAbinding mutant have no effect on cell viability Therefore stringent regulation of the cellular yy2 content might be needed to ensure proper neurite outgrowth and cell vitalityDuring brain development exact temporal and spatial regulation of cellular processes are essential for the proper functional maturation of neuronal connectivities Neurite outgrowth axonal guidance and dendritic development all of which occur during neuronal differentiation are crucial cellular events for the establishment of the neuronal network da Silva and Dotti 2002 In this context primary cultured hippocampal neurons are a wellcharacterized system for studying the molecular mechanisms that regulate changes of neurite morphology Dent et al 2004 Schwamborn et al 2006 In vitro specific stages of neuronal differentiation are characterized by the following morphological characteristics after attaching to the substrate neurons form lamellipodia stage 1 and within a few hours several short undifferentiated processes of similar length called neurites are formed stage 2 After 24–48 h one of these neurites is selected to become the axon and begins to elongate rapidly whereas the length of the other neurites is not substantially changed stage 3 Several days later the remaining neurites begin to grow and differentiate into dendrites stage 4 The axon and dendrites then reach maturation and the neurons form synaptic contacts stage 5 Dotti et al 1988 The transformation from stage 2 to stage 3 is the crucial step in neuronal differentiation when one neurite becomes the axon and thereby the neuron acquires a polar morphology This process involves the coordinated assembly and activation of a number of signaling molecules and their transcriptional regulatory downstream targets to control axon specificationThe biological impact of the transcription factor YinYang 1 YY1 in neurogenesis has been intensively studied He and CasacciaBonnefil 2008 However a distinct functional implication of its homolog YY2 in neuronal development has not yet been described YY2 shares a variety of structural and functional similarities with YY1 Both proteins recognize an identical DNAbinding element with a highly conserved Cterminal C2H2zinc finger domain Kim et al 2007 Luo et al 2006 Nguyen et al 2004 Once bound to DNA these transcription factors can act as activators or repressors Usheva and Shenk 1996 Depending on the particular target gene both YYproteins can mediate either identical or contrary transcriptional activities Chen et al 2010 Klar and Bode 2005Without specific antibodies against mouse yy2 the cellular content of this protein was initially estimated by analyzing the content of yy2 mRNA At first the differential expression pattern of yy2 mRNA in the brain was visualized by in situ hybridization techniques Luo et al 2006 For a better understanding of the region or celltypespecific yy2 expression we performed quantitative polymerase chain reaction qPCR expression analyses in the developing murine brain and in neurons astrocytes and microglia Drews et al 2009 Thereby we identified spatial and temporal differences in yy2 expression levels in the neocortex and cerebellum supporting the specific regulatory functions of yy2 within these tissues at particular developmental stages Moreover we found lower yy2 levels in neurons compared with astrocytes or microgliaIn our present study we show that the length of the major neurite is directly deregulated by knockdown or overexpression of the cellular yy2 expression Furthermore yy2 overexpression influences the number of neuronal processes in proximate extensions We have evidence that cofactors are essentially involved in this process Our experiments imply a functional role of yy2 for proper neurite development

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