MCPH1-mediated Network Regulates Neurogenesis and Neural Stem Cell Fate

人类原发性小头畸形(MCPH)是一种常染色体隐性遗传性神经发育障碍，其特征是脑体积明显缩小，结构正常，非进行性智力低下。MCPH基因可能是在进化过程中人类大脑大小扩大的重要正向选择的结果。编码MCPH1的MCPH1基因参与了细胞周期检查点和DNA损伤反应(DDR)。在DFG支持的最后一段时间里，我们发现小鼠的MCPH1缺失会影响Chk1-CDK1的激活，导致过早进入有丝分裂，从而分散细胞分裂模式并耗尽神经前体细胞池。我们还发现，MCPH1的缺失使神经前体细胞对DDR诱导的细胞凋亡敏感。最近，我们发现MCPH1与泛素E3连接酶BetaTrCP2相互作用，促进其降解CDc25A的活性，从而调节有丝分裂的进入。此外，MCPH1在有丝分裂过渡过程中被另一种E3连接酶APC/CCDH泛素化和降解，这表明MCPH1在有丝分裂过程中的更新是重要的。MCPH1与βTrCP2和APC/CCdh1结合的动态平衡确保了有丝分裂的进出和适当的神经发生。因此，MCPH1的相互作用伙伴被认为是控制神经前体细胞命运和池的重要协调者。要破译MCPH1如何协调细胞活动来控制神经前体细胞的命运和池仍然难以捉摸。在本项目中，我们建议：(1)剖析MCPH1及其相互作用伙伴在脑大小确定和神经退行性变中的功能域。(2)研究MCPH1-betaTrCP2-CDc25A介导的调控有丝分裂进入和神经发生的途径：(3)寻找MCPH1在神经发生和神经干细胞命运决定中驱动MCPH1功能的新的分子途径。我们将采取以下方法：(I)对携带结构域特异性突变MCPH1的小鼠进行鉴定；(Ii)构建缺失特定BetaTrCP2相互作用结构域的MCPH1突变小鼠；(Iii)对MCPH1在有丝分裂进入和神经干细胞命运决定中的新伙伴进行蛋白质组筛选和功能测试。我们的研究将有助于对大脑大小控制的理解。这个项目对于理解小头畸形和认知障碍的一般潜在机制是非常重要的。这些知识可能有助于开发治疗神经退行性部件的新策略。

Human primary microcephaly (MCPH) is an autosomal recessive neurodevelopmental disorder, which is characterized by a marked reduction in brain size with a normal architecture and non-progressive mental retardation. MCPH genes may present a consequence of an important positive selection for the enlargement of the human brain size during evolution. The MCPH1 gene that encodes Microcephalin or MCPH1 has been shown to be involved in cell cycle checkpoint and DNA damage response (DDR). During the last period of DFG support we showed that an MCPH1 deletion in mice affects the Chk1-Cdk1 activation leading to a premature mitotic entry, which distracts cell division mode and exhausts the neuroprogenitor pool. We also found that the MCPH1 deletion sensitizes neuroprogenitors to DDR induced apoptosis. Recently, we discovered that MCPH1 interacts with the ubiquitin E3 ligase betaTrCP2 and promotes its activity to degrade Cdc25A, thereby regulating the mitotic entry. Furthermore, MCPH1 is ubiquitylated and degraded during the mitosis transition by another E3 ligase APC/CCdh, indicating an importance of the MCPH1 turnover during mitosis. A dynamic homeostasis of MCPH1 in association with betaTrCP2 and APC/CCdh1 ensures the mitotic entry and exit and a proper neurogenesis. Thus, the interaction partners of MCPH1 are thought to be important coordinators to control the fate and pools of neuroprogenitors. To decipher how MCPH1 coordinates cellular activities to control the fate and pools of neuroprogenitors remains elusive. In this project we propose:(1) To dissect the functional domains of MCPH1 and its interaction partners in brain size determination and neurodegeneration. (2) To study the MCPH1-betaTrCP2-Cdc25A mediated pathway in regulating the mitotic entry and neurogenesis.(3) To identify novel molecular pathways of MCPH1 which drive the MCPH1 function in neurogenesis and neural stem cell fate determination. We will take the following approaches: (i) The characterization of mice carrying the domain specific mutant MCPH1; (ii) The construction of MCPH1 mutant mice in which the specific betaTrCP2 interaction domain is deleted; (iii) The proteomic screening and functional test of novel MCPH1 partners in the mitotic entry and neural stem cell fate determination. Our study will contribute to the understanding of brain size control. This project is very important for understanding the mechanisms that may be generally underlying microcephaly and cognitive disorders. Such knowledge may facilitate the development of novel strategies for the treatment of neurodegenerative components.