Egger Boris, Leemans Ronny, Loop Thomas, Kammermeier Lars, Fan Yun, Radimerski Tanja, Strahm Martin C, Certa Ulrich, Reichert Heinrich
Biozentrum/Pharmazentrum, University of Basel, CH-4056 Basel, Switzerland.
Development. 2002 Jul;129(14):3295-309. doi: 10.1242/dev.129.14.3295.
In Drosophila, the glial cells missing (gcm) gene encodes a transcription factor that controls the determination of glial versus neuronal fate. In gcm mutants, presumptive glial cells are transformed into neurons and, conversely, when gcm is ectopically misexpressed, presumptive neurons become glia. Although gcm is thought to initiate glial cell development through its action on downstream genes that execute the glial differentiation program, little is known about the identity of these genes. To identify gcm downstream genes in a comprehensive manner, we used genome-wide oligonucleotide arrays to analyze differential gene expression in wild-type embryos versus embryos in which gcm is misexpressed throughout the neuroectoderm. Transcripts were analyzed at two defined temporal windows during embryogenesis. During the first period of initial gcm action on determination of glial cell precursors, over 400 genes were differentially regulated. Among these are numerous genes that encode other transcription factors, which underscores the master regulatory role of gcm in gliogenesis. During a second later period, when glial cells had already differentiated, over 1200 genes were differentially regulated. Most of these genes, including many genes for chromatin remodeling factors and cell cycle regulators, were not differentially expressed at the early stage, indicating that the genetic control of glial fate determination is largely different from that involved in maintenance of differentiated cells. At both stages, glial-specific genes were upregulated and neuron-specific genes were downregulated, supporting a model whereby gcm promotes glial development by activating glial genes, while simultaneously repressing neuronal genes. In addition, at both stages, numerous genes that were not previously known to be involved in glial development were differentially regulated and, thus, identified as potential new downstream targets of gcm. For a subset of the differentially regulated genes, tissue-specific in vivo expression data were obtained that confirmed the transcript profiling results. This first genome-wide analysis of gene expression events downstream of a key developmental transcription factor presents a novel level of insight into the repertoire of genes that initiate and maintain cell fate choices in CNS development.
在果蝇中，神经胶质细胞缺失（gcm）基因编码一种转录因子，该转录因子控制神经胶质细胞与神经元命运的决定。在gcm突变体中，假定的神经胶质细胞会转变为神经元，相反，当gcm异位错误表达时，假定的神经元会变成神经胶质细胞。尽管人们认为gcm通过作用于执行神经胶质细胞分化程序的下游基因来启动神经胶质细胞的发育，但对这些基因的身份却知之甚少。为了全面鉴定gcm的下游基因，我们使用全基因组寡核苷酸阵列来分析野生型胚胎与gcm在整个神经外胚层中均错误表达的胚胎之间的差异基因表达。在胚胎发育过程中的两个特定时间窗口对转录本进行了分析。在gcm对神经胶质细胞前体决定的最初作用的第一阶段，超过400个基因受到差异调节。其中有许多编码其他转录因子的基因，这突出了gcm在神经胶质细胞生成中的主要调控作用。在稍后的第二阶段，当神经胶质细胞已经分化时，超过1200个基因受到差异调节。这些基因中的大多数，包括许多染色质重塑因子和细胞周期调节因子的基因，在早期并没有差异表达，这表明神经胶质细胞命运决定的遗传控制与维持分化细胞所涉及的遗传控制有很大不同。在这两个阶段，神经胶质细胞特异性基因均上调，而神经元特异性基因均下调，这支持了一种模型，即gcm通过激活神经胶质细胞基因同时抑制神经元基因来促进神经胶质细胞的发育。此外，在这两个阶段，许多以前未知参与神经胶质细胞发育的基因都受到差异调节，因此被确定为gcm潜在的新下游靶点。对于一部分差异调节基因，获得了组织特异性的体内表达数据，证实了转录本分析结果。对关键发育转录因子下游的基因表达事件进行的首次全基因组分析，为启动和维持中枢神经系统发育中细胞命运选择的基因库提供了新的深入见解。
