Glutamatergic neurons in the cerebral cortex are derived from embryonic neural stem cells known as radial glial progenitors (RGPs). Early RGPs, present at the onset of cortical neurogenesis, are classically thought to produce columnar clones of glutamatergic neurons spanning the cortical layers. Recently, however, it has been reported that a subset of early RGPs may undergo early commitment to upper layer neuron fates, thus bypassing genesis of deep layer neurons. However, the latter mode of early RGP differentiation was not confirmed in some other studies, and remains controversial. To further investigate the clonal output from early RGPs, we employed genetic lineage tracing driven by Sox9, a transcription factor gene that is expressed in all early RGPs. We found that early RGPs produced columnar clones spanning all cortical layers, with no evidence of significant laminar fate restriction. These data support the classic progressive restriction model of cortical neurogenesis, and suggest that early RGPs do not undergo early commitment to only upper or lower layer fates.

中文翻译：

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新皮质Sox9 +放射状胶质细胞可为所有层产生谷氨酸能神经元，但缺乏早期层状命运限制的明显证据。

大脑皮层中的谷氨酸能神经元衍生自称为radial神经胶质祖细胞（RGP）的胚胎神经干细胞。传统上认为，存在于皮层神经发生开始时的早期RGP产生跨越皮层的谷氨酸能神经元的柱状克隆。然而，最近，据报道，早期RGP的子集可能经历对上层神经元命运的早期承诺，从而绕过了深层神经元的发生。但是，早期RGP分化的后一种模式在其他一些研究中尚未得到证实，并且仍存在争议。为了进一步研究早期RGP的克隆输出，我们采用了由Sox9驱动的遗传谱系追踪，Sox9是在所有早期RGP中表达的转录因子基因。我们发现早期的RGP产生了跨越所有皮质层的柱状克隆，没有明显的层流命运限制的证据。这些数据支持经典的皮质神经发生的渐进性限制性模型，并表明早期RGP不会仅对上层或下层命运进行早期承诺。