Arx acts as a key selector gene of the ventral telencephalon mainly through its repression transcriptional activity

The homeobox containing gene Arx is expressed during ventral telencephalon development and it is required for correct GABAergic interneuron tangential migration from the ganglionic eminences to the olfactory bulbs, cerebral cortex and striatum. Its human ortholog is associated with a variety of neurological clinical manifestations whose syntoms are compatible with a loss of cortical interneurons and altered basal ganglia related-activities in humans. Herein, we reported the identification by global expression profiling of a group of genes whose expression is consistently altered in Arx mutant ganglionic eminences. Following analysis revealed the striking ectopic expression in the ganglionic eminences of a number of genes normally not, or only marginally, expressed in the ventral telencephalon. Among them, we functionally analyzed Ebf3, whose ectopic expression in ventral telencephalon is preventingneuronal tangential migration. Further, we showed that Arx is sufficient to repress Ebf3 endogenous expression and that its silencing in Arx mutant tissue might marginally rescue tangential cell movements. Together, these data provide an initial analysis of the molecular pathways regulated by Arx and how their networking might regulate those specific cellular processes during telencephalon development strongly altered by loss of Arx. Three timed-pregnant Arx heterozygous dams crossed with C57Bl/6 males were sacrificed at E14.5, the embryos harvested and placed into cold PBS. After brain isolation, meninges and olfactory bulbs were removed, and the ventral telencephalon separated from the overlying cerebral cortex. The same procedure was repeated for 5 wt and 5 Arx mutant embryos.含同源框的基因Arx（homeobox-containing gene Arx）在腹侧端脑发育过程中表达，且对于γ-氨基丁酸能（GABAergic）中间神经元从神经节隆起（ganglionic eminences）向嗅球（olfactory bulbs）、大脑皮层（cerebral cortex）及纹状体（striatum）的正常切线迁移（tangential migration）不可或缺。其人类同源基因（human ortholog）与多种神经科临床表现相关，此类临床表现的症状与人类皮层中间神经元丢失及基底节相关活动异常高度契合。本研究通过全局表达谱分析（global expression profiling），鉴定出在Arx突变型（mutant）神经节隆起中表达水平持续异常的一组基因。后续分析发现，多个通常不在腹侧端脑表达、或仅微量表达的基因在神经节隆起中出现了显著的异位表达（ectopic expression）。其中，我们针对Ebf3开展了功能分析（functional analysis），证实其在腹侧端脑的异位表达会阻碍神经元的切线迁移。此外，我们证明Arx足以抑制Ebf3的内源性表达（endogenous expression），且在Arx突变组织中沉默Ebf3可轻度挽救切线式细胞迁移过程。综上，本研究数据首次解析了Arx调控的分子通路，以及这些通路的调控网络如何调控端脑发育过程中因Arx缺失而发生显著异常的特定细胞过程。本研究选取3只与C57Bl/6雄鼠交配的Arx杂合定时受孕雌鼠，于胚胎发育第14.5天（E14.5）处死，收集胚胎并置于预冷的磷酸盐缓冲液（PBS）中。分离脑组织后，去除脑膜与嗅球，并将腹侧端脑与上方覆盖的大脑皮层分离。我们对5只野生型（wt）胚胎与5只Arx突变型胚胎重复了相同的实验流程。