Caviness V S, Takahashi T
Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Brain Dev. 1995 May-Jun;17(3):159-63. doi: 10.1016/0387-7604(95)00029-b.
The neocortex varies vastly in size and complexity yet its cytology, laminar architecture, and general plan of cytoarchitectonic organization are closely similar across mammalian species. These similarities of structure and organization emerge in the course of a closely similarly developmental history. Thus, the neocortex in all species arises in the course of a discrete neuronogenetic interval (NI) from a pseudostratified ventricular epithelium (PVE) located in the margin of the developing cerebral wall. Once their terminal cell division in this epithelium has been completed the young neurons migrate across the cerebral wall to the neocortex where they grow, differentiate, and become synaptically incorporated into cerebral neural systems. The neurons forming the deepest cortical layers are the earliest to be formed while progressively later formed neurons arise at progressively later times in development. In experiments in mice, we have determined that it is the relation of total cell cycle number, occurring in the course of the NI, to the cell cycle output function, Q, which is regulatory to the duration of NI and to the rate of neuron production. Cell cycle number appears largely to be regulated by progression in the length of the G1 phase of the cycle. We propose that regulation is mediated by cell external substances, acting upon the proliferating cell during G1 phase.
新皮层在大小和复杂性上差异巨大，但其细胞学、分层结构以及细胞构筑组织的总体模式在哺乳动物物种间却极为相似。这些结构和组织上的相似性在相似的发育历程中显现出来。因此，所有物种的新皮层都是在一个离散的神经元发生期（NI）内，由位于发育中脑壁边缘的假复层室管膜上皮（PVE）产生的。一旦它们在该上皮中的终末细胞分裂完成，年轻的神经元就会穿过脑壁迁移到新皮层，在那里它们生长、分化，并通过突触整合到脑神经系统中。形成最深皮层层的神经元最早形成，而逐渐后形成的神经元则在发育过程中逐渐在较晚的时间出现。在小鼠实验中，我们已经确定，在NI过程中发生的总细胞周期数与细胞周期输出函数Q的关系，对NI的持续时间和神经元产生速率具有调节作用。细胞周期数似乎很大程度上受细胞周期G1期长度进展的调节。我们提出，这种调节是由细胞外物质介导的，这些物质在G1期作用于增殖细胞。
