Molecular cell-biological studies on differentiation and mitotic arrest of brain neurons

脊椎动物中枢神经系统中的神经元在从其增殖的前体细胞分化后立即永久地退出细胞周期。为了研究神经元分裂后的分子机制，我们重点研究了从胚胎癌细胞P19中分离出来的神经元生长抑制因子Necdin的功能作用和分子特性。取得的结果如下。[1]Necdin与视网膜母细胞瘤蛋白(Rb)一样，与猴病毒40(SV40)大T抗原和腺病毒E1a的转化域结合。[2]Necdin与E2F-1结合，E2F-1是一种促进细胞周期并抑制其功能的细胞转录因子。[3]在Rb缺乏的SAOS-2细胞中，Necdin的异位表达抑制了细胞的生长，表明Necdin是Rb的功能性替代品。[4]重组Necdin蛋白的抗体在小鼠脑神经元的胞浆中与Necdin反应，在下丘脑的免疫反应性最高。[5]人Necdin基因的5‘端序列含有频繁的CpG二核苷酸(鉴定为CpG岛)，启动子区域的CpG二核苷酸体外甲基化抑制了转录活性。[6]人类Necdin基因定位于染色体15q11.2-q12，该区域与Prader-Willi综合征有关，这是一种与基因组印记相关的神经行为障碍。[7]综上所述，Necdin抑制细胞生长的方式与Rb相似，其缺乏可能导致神经元分化的缺陷。

Neurons in the vertebrate central nervous system CNS withdraw permanently from the cell cycle immediately after differentiation from their proliferative progenitors. To study the molecular mechanism whereby neurons become postmitotic, we focused on the functional roles and molecular properties of necdin, a neuronal growth suppressor isolated from embryonal carcinoma P19 cells. Results obtained are as follows. [1] Necdin, like retinoblastoma protein (Rb), bound to transforming domains of simian virus 40 (SV40) large T antigen and adenovirus E1A.[2] Necdin bound to E2F-1, a cellular transcription factor that promotes the cell cycle, and suppressed its functions. [3] Ectopic expression of necdin in Rb-dificient SAOS-2 cells suppressed the cell growth, indicating that necdin is a functional substitute for Rb. [4] An antibody against recombinant necdin protein reacted with necdin in the cytoplasm of mouse brain neurons, and the immunoreactivity was the highest in the hypothalamus.[5] The 5'-end sequence of the human necdin gene contains frequent CpG dinucleotides (identified as a CpG island), and methylation in vitro of CpG dinucleotides in the promoter region suppressed the transcriptional activity. [6] The human necdin gene was localized to chromosome 15q11.2-q12, which lies within the region involved in Prader-Willi syndrome, a genomic imprinting-associated neurobehavioral disorder. [7] In summary, necdin suppresses cell growth in a manner similar to that of Rb, and its deficiency may cause the defect of neuronal differentiation.