Molecular and cellular mechanism of Microcephaly

描述(申请人提供)：常染色体隐性遗传性原发性小头症(MCPH)是一种遗传和临床上不同的疾病，定义为出生时头围减少。患者通常有广泛的神经问题，包括智力低下、局灶性或全身性癫痫、多动症和注意力缺陷障碍。无重大结构异常的脑体积减少很可能源于神经发生和/或神经元迁移的原发缺陷。在整个或部分细胞周期中，8个MCPH基因中有5个定位于中心体。体外研究提供的证据表明，这些基因在重要的中心体功能中发挥作用，如细胞周期调节。尽管如此，MCPH在脑发育中的作用机制仍然知之甚少。该项目的长期目标是描述MCPH基因在新皮质发育和疾病发病机制中的作用。其目的是揭示MCPH基因对神经发生的分子和细胞控制，并确定中心体蛋白如何调节分裂模式(对称或不对称)、神经元迁移和分化。我们实验室和其他实验室最近的研究表明，放射状胶质细胞是神经前体细胞的主要群体。它们不对称分裂以自我更新，并产生皮质神经元。不对称中心体遗传被认为调节了胚胎小鼠新皮质中自我更新祖细胞与分化后代的差异行为。果蝇的中心体缺陷不会显著扰乱大多数体细胞的有丝分裂，但幼虫神经母细胞的不对称分裂被显著扰乱，这突显了中心体行为对前体细胞的不对称分裂和决定子细胞命运的特殊意义。此外，中心体是微管的主要锚，使分化的神经元能够启动和延伸轴突，这是神经元分化的关键过程。基于这些观察，这一应用的中心假设是MCPH基因控制着发育中的皮质中的神经发生、神经元迁移和分化。在强大的初步数据的指导下，这一假说将通过四个具体目标进行验证：1)确定MCPH基因调控放射状胶质细胞分裂的分子和细胞机制；2)探索MCPH基因在调节母女中心体和子细胞命运不对称遗传中的功能；3)确定MCPH基因在调节发育中的皮质中神经元迁移和分化的功能；以及4)利用患者诱导的多能干细胞(IPS)验证在小鼠中的发现与人类MCPH发病机制的相关性。利用高时间延时成像和分子遗传学技术等创新手段，这项研究将为MCPH的发病机制提供新的见解，并扩大我们对脑发育的了解。此外，这项研究的结果可能有助于阐明许多与皮质功能相关的神经和精神疾病的病因学机制。

DESCRIPTION (provided by applicant): Autosomal recessive primary microcephaly (MCPH) is a genetically and clinically heterogeneous disease defined by a decrease in head circumference at birth. Patients often have a broad spectrum of neurological problems, including mental retardation, focal or generalized seizures, hyperactivity, and attention deficit disorder. The decrease in brain volume without major architectonic abnormalities most likely stems from a primary defect in neurogenesis and or neuronal migration. Five of eight MCPH genes localize to the centrosome during all or part of the cell cycle. In vitro studies provide evidence that these genes play roles in essential centrosomal functions such as cell cycle regulation. Nonetheless, the mechanism of MCPH in brain development is still poorly understood. The long-term goal of this project is to profile the role of MCPH genes in neocortical development and disease pathogenesis. The objectives are to uncover the molecular and cellular controls of MCPH genes on neurogenesis and to define how centrosomal proteins regulate the mode of division (symmetric or asymmetric), neuronal migration and differentiation. Recent studies from our lab and others have demonstrated that radial glial cells are a major population of neuronal progenitor cells. They divide asymmetrically to self-renew and give rise to cortical neurons. Asymmetric centrosome inheritance is believed to regulate the differential behavior of self-renewing progenitors versus differentiating progeny in the embryonic mouse neocortex. Centrosome defects in Drosophila do not dramatically perturb mitosis in most somatic cells, but the asymmetric division of larval neuroblasts is noticeably disrupted, underscoring the particular significance of centrosome behavior for asymmetric cell division of progenitor cells and determination of daughter cell fate. Furthermore, the centrosome is the primary anchor for microtubules, enabling the differentiating neuron to initiate and extend an axon, a key process of neuron differentiation. Based on these observations, the central hypothesis of this application is that the MCPH genes control neurogenesis, neuronal migration, and differentiation in the developing cortex. Guided by strong preliminary data this hypothesis will be tested by pursuing four specific aims: 1) To determine the molecular and cellular mechanism by which MCPH genes regulate radial glial cell division; 2) To explore the function of MCPH genes in regulating asymmetric inheritance of mother versus daughter centrosomes and daughter cell fate; 3) To define the function of MCPH genes in regulating neuronal migration and differentiation in the developing cortex; and 4) To validate the relevance of findings in the mouse to the pathogenesis of human MCPH using patient induced pluripotent stem (iPS) cells. With innovative approaches including high-temporal time-lapse imaging and molecular genetic techniques, the proposed research will provide new insights into the pathogenesis of MCPH and expand our knowledge of brain development. Moreover, the results of this study may shed light on mechanisms relevant to the etiology of many neurological and psychiatric disorders related to cortical function.