Department of Pathology and Laboratory Medicine, School of Medicine, University of California Davis, Sacramento, California, United States of America.
PLoS One. 2012;7(1):e30178. doi: 10.1371/journal.pone.0030178. Epub 2012 Jan 17.
The mammalian cerebral cortex arises from precursor cells that reside in a proliferative region surrounding the lateral ventricles of the developing brain. Recent work has shown that precursor cells in the subventricular zone (SVZ) provide a major contribution to prenatal cortical neurogenesis, and that the SVZ is significantly thicker in gyrencephalic mammals such as primates than it is in lissencephalic mammals including rodents. Identifying characteristics that are shared by or that distinguish cortical precursor cells across mammalian species will shed light on factors that regulate cortical neurogenesis and may point toward mechanisms that underlie the evolutionary expansion of the neocortex in gyrencephalic mammals. We immunostained sections of the developing cerebral cortex from lissencephalic rats, and from gyrencephalic ferrets and macaques to compare the distribution of precursor cell types in each species. We also performed time-lapse imaging of precursor cells in the developing rat neocortex. We show that the distribution of Pax6+ and Tbr2+ precursor cells is similar in lissencephalic rat and gyrencephalic ferret, and different in the gyrencephalic cortex of macaque. We show that mitotic Pax6+ translocating radial glial cells (tRG) are present in the cerebral cortex of each species during and after neurogenesis, demonstrating that the function of Pax6+ tRG cells is not restricted to neurogenesis. Furthermore, we show that Olig2 expression distinguishes two distinct subtypes of Pax6+ tRG cells. Finally we present a novel method for discriminating the inner and outer SVZ across mammalian species and show that the key cytoarchitectural features and cell types that define the outer SVZ in developing primates are present in the developing rat neocortex. Our data demonstrate that the developing rat cerebral cortex possesses an outer subventricular zone during late stages of cortical neurogenesis and that the developing rodent cortex shares important features with that of primates.
哺乳动物大脑皮层起源于位于发育中大脑侧脑室周围的增殖区的前体细胞。最近的工作表明，室下区 (SVZ) 的前体细胞对产前皮质神经发生有重大贡献，并且在灵长类等脑回哺乳动物中，SVZ 比包括啮齿类动物在内的脑平滑哺乳动物明显更厚。确定在哺乳动物物种之间共享或区分皮质前体细胞的特征将揭示调节皮质神经发生的因素，并可能指向脑回哺乳动物新皮质进化扩张的机制。我们对脑回哺乳动物 (雪貂和猕猴) 和脑平滑哺乳动物 (大鼠) 的发育大脑皮层进行了免疫染色，以比较每种物种前体细胞类型的分布。我们还对发育中的大鼠新皮层中的前体细胞进行了延时成像。我们发现，Pax6+ 和 Tbr2+ 前体细胞的分布在脑平滑大鼠和脑回雪貂中相似，而在猕猴的脑回皮层中则不同。我们发现，有丝分裂的 Pax6+ 迁移性放射状胶质细胞 (tRG) 在每个物种的神经发生期间和之后都存在于大脑皮层中，这表明 Pax6+ tRG 细胞的功能不仅限于神经发生。此外，我们发现 Olig2 表达可将 Pax6+ tRG 细胞区分成两种不同的亚型。最后，我们提出了一种跨哺乳动物物种区分内、外 SVZ 的新方法，并表明在发育中的灵长类动物中，定义外 SVZ 的关键细胞结构和细胞类型也存在于发育中的大鼠新皮层中。我们的数据表明，在皮质神经发生的晚期，发育中的大鼠大脑皮层具有一个外 SVZ，并且发育中的啮齿动物皮层与灵长类动物具有重要的共同特征。
