Mione M C, Danevic C, Boardman P, Harris B, Parnavelas J G
Department of Anatomy and Developmental Biology, University College London, United Kingdom.
J Neurosci. 1994 Jan;14(1):107-23. doi: 10.1523/JNEUROSCI.14-01-00107.1994.
Studies of cell lineage in the rat cerebral cortex have provided new insights into the mechanisms of neuronal and glial determination. They have shown that clonally related cells, marked with retrovirus injection at embryonic day 16 (E16), express the same glial or neuronal phenotype, suggesting that separate progenitors for each of these cell phenotypes exist in the ventricular zone at that stage of corticogenesis. However, it is not known if such committed progenitors are present in the ventricular zone before E16. Another important question concerns which neurochemical features are shared by clonally related cells of the adult cerebral cortex. In this study we have addressed the first question by injecting a retroviral vector expressing beta-galactosidase into the telencephalic ventricles of rat embryos at different stages (E14-E19). In order to classify clonally related neurons in the cerebral cortex of these rats, we have used postembedding immunohistochemistry for the amino acid neurotransmitters glutamate, aspartate, and GABA. Glutamate and GABA immunoreactivity marked nonoverlapping populations of cells that corresponded to the pyramidal and nonpyramidal neuron types of the rat cerebral cortex. Clonally related neurons, marked by retrovirus injection at any day between E14 and E19, homogeneously expressed one or other phenotype and accordingly displayed glutamate or GABA immunoreactivity. This finding indicates that committed progenitor cells for pyramidal and nonpyramidal neurons are present in the ventricular zone before E16. To investigate whether lineage dictates other features in clonally related neurons, we performed an immunohistochemical analysis for the calcium-binding proteins calbindin, parvalbumin, and calretinin in clusters of clonally related nonpyramidal neurons. The same calcium-binding protein was rarely found in members of the same cluster, suggesting that lineage does not control the expression of calcium-binding proteins in cortical nonpyramidal neurons. As a result of examining a large number of clonally related neurons from brains injected at different ages, we observed remarkable differences in number and laminar distribution of pyramidal and nonpyramidal neurons marked with retrovirus. Clusters of nonpyramidal neurons were usually composed of two or three cells, and resided in the cortical layers that were just being generated at the time of injection. Clusters of pyramidal neurons were larger and dispersed in several layers in the earlier injections; their size and laminar distribution were progressively reduced for later injections. These observations suggest the existence of different mechanisms that generate the pyramidal and nonpyramidal neurons of the cerebral cortex.
对大鼠大脑皮质细胞谱系的研究为神经元和神经胶质细胞分化机制提供了新的见解。这些研究表明，在胚胎第16天（E16）通过逆转录病毒注射标记的克隆相关细胞表达相同的神经胶质或神经元表型，这表明在皮质发生的那个阶段，脑室区存在着分别产生这些细胞表型的祖细胞。然而，尚不清楚在E16之前脑室区是否存在这种定向祖细胞。另一个重要问题是，成年大脑皮质的克隆相关细胞共享哪些神经化学特征。在本研究中，我们通过在不同阶段（E14 - E19）将表达β-半乳糖苷酶的逆转录病毒载体注入大鼠胚胎的端脑室来解决第一个问题。为了对这些大鼠大脑皮质中的克隆相关神经元进行分类，我们对氨基酸神经递质谷氨酸、天冬氨酸和GABA采用了包埋后免疫组织化学方法。谷氨酸和GABA免疫反应标记了不重叠的细胞群体，分别对应于大鼠大脑皮质的锥体神经元和非锥体神经元类型。在E14至E19之间的任何一天通过逆转录病毒注射标记的克隆相关神经元，均均匀地表达一种或另一种表型，因此显示出谷氨酸或GABA免疫反应性。这一发现表明，锥体神经元和非锥体神经元的定向祖细胞在E16之前就已存在于脑室区。为了研究谱系是否决定克隆相关神经元的其他特征，我们对克隆相关的非锥体神经元簇进行了钙结合蛋白钙结合蛋白、小白蛋白和钙视网膜蛋白的免疫组织化学分析。在同一簇的细胞中很少发现相同的钙结合蛋白，这表明谱系并不控制皮质非锥体神经元中钙结合蛋白的表达。通过检查来自不同年龄注射大脑的大量克隆相关神经元，我们观察到用逆转录病毒标记的锥体神经元和非锥体神经元在数量和层状分布上存在显著差异。非锥体神经元簇通常由两三个细胞组成，位于注射时正在生成的皮质层中。锥体神经元簇在早期注射时较大且分散在几层中；后期注射时，它们的大小和层状分布逐渐减小。这些观察结果表明，存在不同的机制来产生大脑皮质的锥体神经元和非锥体神经元。
