Neurogenesis of GABAergic neurons in the neocortex

在发育中的啮齿动物新皮层中，多巴胺能神经元由苍白球室区（VZ）放射状胶质细胞增殖提供，而GABA能神经元则产生于苍白球下结构的神经节隆起（GE），然后通过切向细胞迁移进入新皮层。然而，用逆转录病毒进行的细胞谱系分析经常揭示出克隆相关的GABA能神经元对紧密地位于新皮层内。根据这些报道，我们推测，一些GABA能神经元产生于啮齿动物的新皮层。在GAD 67-GFP基因敲入小鼠中，我们发现单脉冲（30分钟）BrdU和GFP，或Ki-67和GFP在出生时的脑室下区（SVZ）和新皮质的中间区（IZ）中共定位。SVZ和IZ中四分之一的GFP阳性细胞为Ki-67阳性。新皮层中三分之一的GFP阳性细胞对巢蛋白呈阳性。这些数据表明，一部分GAD 67阳性细胞是增殖的，表明这些细胞是定向为GABA能神经元的祖细胞。为了评估GABA能神经元的假定祖细胞是否也由GE的切向细胞迁移提供，我们将腺病毒或逆转录病毒与构建体（CA启动子-loxP-GFP-loxP）一起注射到Emx 1-Cre基因敲入小鼠胚胎的脑室中：这些病毒揭示了新皮质中Emx 1阴性细胞的起源。我们发现新皮层中的一些假定的GABA能神经元祖细胞是Emx 1阴性的，并且来源于苍白球下VZ。我们的结论是，GABA能神经元在啮齿类动物的新皮层不仅提供了有丝分裂后的GABA能神经元从GE的迁移，但也通过增殖的祖细胞从GE迁移到新皮层。

In the developing rodent neocortex, the glutamatergic neurons are supplied by proliferation of radial glias in the ventricular zone(VZ) of the pallium, while the GABAergic neurons are produced in the the ganglionic eminence(GE), a subpallial structure, and then come into the neocortex by tangential cell migration. However, cell lineage analyses with a retrovirus have often revealed clonally related GABAergic neuron pairs located closely within the neocortex. Following these reports, we speculated that some of the GABAergic neurons were produced in the rodent neocortex. In GAD67-GFP knock-in mice, we found colocalization of single-pulse (30 min) BrdU and GFP, or Ki-67 and GFP in the subventricular zone(SVZ)and the intermediate zone(IZ) of the neocortex at birth. One forth of GFP-positive cells in the SVZ and the IZ were positive for Ki-67. And one thirds of GFP-positive cells in the neocortex were positive for nestin. These data indicate that a portion of GAD67-positivecells are proliferative, suggesting these cells are the progenitorscommitted to GABAergic neurons. To assess whether the putative progenitors for GABAergic neurons were also supplied by tangential cellmigration from the GE, we injected an adenovirus or retrovirus witha construct (CA promoter-loxP-GFP-loxP) into the ventricle of Emx1-Cre knock-in mouse embryos : These viruses reveal the origin of the Emx1-negative cells in the neocortex. We found some of the putative GABAergic neuron progenitors in the neocortex were in Emx1-negativelineage and derived from the subpallial VZ. We conclude that the GABAergic neurons in the rodent neocortex are supplied not only by migration of postmitotic GABAergic neurons from the GE, but also by proliferation of their progenitors immigrated from the GE to the neocortex.