MCPH1-mediated Network Regulates Neurogenesis and Neural Stem Cell Fate

人类原发性小头畸形（Human primary microcephaly，MCPH）是一种常染色体隐性遗传的神经发育障碍，其特征是脑体积显著减小，结构正常，智力发育迟缓。MCPH基因可能是进化过程中人类大脑体积扩大的重要正选择的结果。编码Microcephalin或MCPH 1的MCPH 1基因已被证明参与细胞周期检查点和DNA损伤反应（DDR）。在DFG支持的最后一个时期，我们发现小鼠中的MCPH 1缺失影响Chk 1-Cdk 1激活，导致过早的有丝分裂进入，这分散了细胞分裂模式并耗尽了神经祖细胞库。我们还发现，MCPH 1缺失使神经祖细胞对DDR诱导的凋亡敏感。最近，我们发现MCPH 1与泛素E3连接酶betaTrCP 2相互作用，并促进其降解Cdc 25 A的活性，从而调节有丝分裂进入。此外，MCPH 1在有丝分裂过渡期间被另一种E3连接酶APC/CCdh泛素化和降解，表明MCPH 1在有丝分裂期间周转的重要性。MCPH 1与betaTrCP 2和APC/CCDh 1的动态平衡确保了有丝分裂的进入和退出以及适当的神经发生。因此，MCPH 1的相互作用伙伴被认为是控制神经祖细胞命运和库的重要协调者。要破译MCPH 1如何协调细胞活动以控制神经祖细胞的命运和池仍然是难以捉摸的。在本项目中，我们提出：（1） 分析MCPH 1及其相互作用伙伴在脑大小决定和神经退行性变中的功能域。（二） 研究MCPH 1-betaTrCP 2-Cdc 25 A通路对有丝分裂进入和神经发生的调控作用。（三） 确定MCPH 1在神经发生和神经干细胞命运决定中驱动MCPH 1功能的新分子途径。我们将采取以下方法：（i）携带结构域特异性突变体MCPH 1的小鼠的表征;（ii）缺失特异性betaTrCP 2相互作用结构域的MCPH 1突变小鼠的构建;（iii）新MCPH 1伴侣在有丝分裂进入和神经干细胞命运决定中的蛋白质组学筛选和功能测试。我们的研究将有助于理解大脑的大小控制。该项目对于理解可能是通常潜在的小头畸形和认知障碍的机制非常重要。这些知识可能有助于开发治疗神经退行性疾病的新策略。

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.