Sanosaka T, Namihira M, Asano H, Kohyama J, Aisaki K, Igarashi K, Kanno J, Nakashima K
Laboratory of Molecular Neuroscience, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara 630-0101, Japan.
Neuroscience. 2008 Aug 26;155(3):780-8. doi: 10.1016/j.neuroscience.2008.06.039. Epub 2008 Jun 21.
During development of the mammalian CNS, neurons and glial cells (astrocytes and oligodendrocytes) are generated from common neural precursor cells (NPCs). However, neurogenesis precedes gliogenesis, which normally commences at later stages of fetal telencephalic development. Astrocyte differentiation of mouse NPCs at embryonic day (E) 14.5 (relatively late gestation) is induced by activation of the transcription factor signal transducer and activator of transcription (STAT) 3, whereas at E11.5 (mid-gestation) NPCs do not differentiate into astrocytes even when stimulated by STAT3-activating cytokines such as leukemia inhibitory factor (LIF). This can be explained in part by the fact that astrocyte-specific gene promoters are highly methylated in NPCs at E11.5, but other mechanisms are also likely to play a role. We therefore sought to identify genes involved in the inhibition of astrocyte differentiation of NPCs at midgestation. We first examined gene expression profiles in E11.5 and E14.5 NPCs, using Affymetrix GeneChip analysis, applying the Percellome method to normalize gene expression level. We then conducted in situ hybridization analysis for selected genes found to be highly expressed in NPCs at midgestation. Among these genes, we found that N-myc and high mobility group AT-hook 2 (Hmga2) were highly expressed in the E11.5 but not the E14.5 ventricular zone of mouse brain, where NPCs reside. Transduction of N-myc and Hmga2 by retroviruses into E14.5 NPCs, which normally differentiate into astrocytes in response to LIF, resulted in suppression of astrocyte differentiation. However, sustained expression of N-myc and Hmga2 in E11.5 NPCs failed to maintain the hypermethylated status of an astrocyte-specific gene promoter. Taken together, our data suggest that astrocyte differentiation of NPCs is regulated not only by DNA methylation but also by genes whose expression is controlled spatio-temporally during brain development.
在哺乳动物中枢神经系统（CNS）发育过程中，神经元和神经胶质细胞（星形胶质细胞和少突胶质细胞）由共同的神经前体细胞（NPCs）产生。然而，神经发生先于胶质发生，胶质发生通常在胎儿端脑发育的后期开始。胚胎第14.5天（相对妊娠后期）小鼠NPCs的星形胶质细胞分化是由转录因子信号转导子和转录激活子（STAT）3的激活诱导的，而在胚胎第11.5天（妊娠中期），即使受到STAT3激活细胞因子如白血病抑制因子（LIF）的刺激，NPCs也不会分化为星形胶质细胞。这部分可以通过以下事实来解释：星形胶质细胞特异性基因启动子在胚胎第11.5天的NPCs中高度甲基化，但其他机制也可能起作用。因此，我们试图鉴定参与抑制妊娠中期NPCs星形胶质细胞分化的基因。我们首先使用Affymetrix基因芯片分析，应用Percellome方法标准化基因表达水平，检测胚胎第11.5天和第14.5天NPCs的基因表达谱。然后，我们对在妊娠中期NPCs中高表达的选定基因进行原位杂交分析。在这些基因中，我们发现N - myc和高迁移率族AT - 钩2（Hmga2）在小鼠脑的胚胎第11.5天而非第14.5天的脑室区高表达，NPCs位于该区域。通过逆转录病毒将N - myc和Hmga2转导到胚胎第14.5天的NPCs中，这些NPCs通常会因LIF而分化为星形胶质细胞，结果导致星形胶质细胞分化受到抑制。然而，在胚胎第11.5天的NPCs中持续表达N - myc和Hmga2未能维持星形胶质细胞特异性基因启动子的高甲基化状态。综上所述，我们的数据表明，NPCs的星形胶质细胞分化不仅受DNA甲基化调控，还受在脑发育过程中时空表达受控制的基因调控。
