Ferri R T, Levitt P
Department of Anatomy and Neurobiology, Medical College of Pennsylvania, Philadelphia 19129.
Cereb Cortex. 1993 May-Jun;3(3):187-98. doi: 10.1093/cercor/3.3.187.
The mammalian cerebral cortex is characterized by its organization into anatomically and functionally discrete regions. During cortical development, a homogeneous-appearing population of cells along the ventricular surface generates the neurons and glia that ultimately form these cytoarchitectonic areas. The limbic system-associated membrane protein (LAMP) is a neuronal, cell surface glycoprotein that identifies neurons restricted to limbic cerebral cortical areas (Levitt, 1984). LAMP is expressed early in development (Horton and Levitt, 1988), and transplantation studies in the rat suggest that cells in the cerebral wall are committed to a limbic or nonlimbic molecular phenotype by embryonic day 14 (E14) (Barbe and Levitt, 1991). However, at E12, cells destined for the cerebral cortex are still multipotential and presumably depend on local, extrinsic signals to adopt a limbic phenotype. We have developed an in vitro assay system for examining the fate of these multipotential progenitors and identifying potential environmental regulators of neuronal differentiation. Regions of the lateral (limbic) and dorsal (nonlimbic) cerebral wall at E12 are dissected, dissociated, and grown in low-density cultures in defined medium. The cells are examined by immunocytochemistry for expression of MAP2, a neuronal cytoskeletal protein, and LAMP to define neuronal differentiation and the expression of a limbic molecular phenotype, respectively. We find that after 4 d in culture, up to 75% of the progenitor cells from presumptive limbic cortex express LAMP upon differentiation. In contrast, only 20-30% of the differentiated cells from presumptive sensorimotor cortex express LAMP. Thus, most cortical progenitors are fated to a limbic or nonlimbic phenotype early in development, and the decision by neuronal stem cells to differentiate into neurons exhibiting this molecular phenotype occurs prior to the completion of neurogenesis, in the absence of subcortical environmental cues.
哺乳动物的大脑皮层具有在解剖学和功能上划分为离散区域的组织特征。在皮层发育过程中，沿着脑室表面看似同质的细胞群体产生了最终形成这些细胞结构区域的神经元和神经胶质细胞。边缘系统相关膜蛋白（LAMP）是一种神经元细胞表面糖蛋白，可识别局限于边缘大脑皮层区域的神经元（莱维特，1984年）。LAMP在发育早期表达（霍顿和莱维特，1988年），大鼠的移植研究表明，到胚胎第14天（E14）时，脑壁中的细胞已确定为边缘或非边缘分子表型（巴贝和莱维特，1991年）。然而，在E12时，注定要进入大脑皮层的细胞仍然具有多能性，大概依赖于局部的外在信号来采用边缘表型。我们开发了一种体外检测系统，用于研究这些多能祖细胞的命运，并确定神经元分化的潜在环境调节因子。在E12时，解剖、分离外侧（边缘）和背侧（非边缘）脑壁区域，并在限定培养基中进行低密度培养。通过免疫细胞化学检查细胞中神经元细胞骨架蛋白MAP2的表达以及LAMP的表达，分别以确定神经元分化和边缘分子表型的表达。我们发现，培养4天后，来自假定边缘皮层的祖细胞中高达75%在分化时表达LAMP。相比之下，来自假定感觉运动皮层的分化细胞中只有20 - 30%表达LAMP。因此，大多数皮层祖细胞在发育早期就注定为边缘或非边缘表型，并且神经元干细胞分化为表现出这种分子表型的神经元的决定在神经发生完成之前就已发生，且不存在皮层下环境线索。
