Molecular mechanisms of lamina-specific neural circuit formation in the neocortex

大脑皮层由六层细胞结构组成，神经连接由其建立。由于这种层状结构不仅存在于大脑皮层中，而且存在于其他中枢神经系统中，因此它被认为是神经回路形成的原理。迄今为止，包括我们的研究（Yamamoto et al，1989，1992，1995，1997）在内的体内和体外发育研究已经证明，每层细胞都具有特定的靶识别机制，以产生传入和传出连接。此外，该机制由以核纤层特异性方式表达的分子调节（Yamamoto等人，2000 a，B）。然而，这些板层特异性分子的存在和功能并不是完全未知的，在本研究中，我们试图鉴定这些板层特异性分子，并揭示它们在皮层回路形成中的作用。为此，通过提取各层RNA构建消减cDNA文库，并用于筛选叶片特异性基因。结果，编码转录因子和细胞表面分子的几个基因被鉴定为第4层或第5层特异性分子。此外，还利用单克隆抗体技术获得了一个属于钙粘蛋白家族的核纤层特异性分子。通过分析发育过程中的表达模式以及基因表达与细胞类型之间的关系，我们认为这些核纤层特异性基因可能参与了细胞类型的特化和皮层回路的形成。

The cerebral cortex is composed of six cell layered structure, by which neural connections are established. As such laminar structure is present in not only the cerebral cortex but also other central nervous systems, it is thought to be a principle for neural circuit formation. To date, developmental studies in vivo and in vitro studies including ours (Yamamoto et al, 1989,1992,1995,1997) have demonstrated that each layer cells have specific target recognition mechanisms to produce afferent and efferent connections. Moreover, the mechanisms are regulated by the molecules that are expressed in a lamina-specific fashion (Yamamoto et al, 2000a,b). However, the presence and function of these lamina-specific molecules were not almost unknown.In this study, we attempted to identify these lamina-specific molecules, and to reveal the involvement of them in cortical circuit formation. To do that, a subtraction cDNA library was constructed by extracting RNAs from each layer, and were applied to screening lamina-specific genes. As a result, several genes which code transcription factors and cell surface molecules were identified as layer 4 or layer 5-specific molecules. Moreover, a lamina-specific molecule, which belongs to cadherin family, was obtained by using monoclonal antibody technique. We suggested that these lamina-specific genes may be involved in cell type specification and cortical circuit formation by analyzing developmental expression patterns and relation between gene expression and cell types.