Mutant DISC 1 and Abnormal Neurodevelopment in Mental Illness

精神分裂症是一种毁灭性的精神疾病，部分原因是大脑发育的细微缺陷。DISC1基因是研究精神分裂症发病机制及与神经发育相关的精神疾病的有力候选基因之一。 在一个患有精神分裂症和其他主要精神疾病的苏格兰大家系中，平衡易位会导致DlSC1基因的缺失，导致一种影响神经发育的截短蛋白产物。尽管已经发展了几种DISC1小鼠模型，但关于突变人(HDISC1)在出生前和出生后的时间选择或持续和可逆影响(HDISC1)的关键问题仍然没有答案。我们建议通过我们的转基因来确定突变型hDISC1作用的时间窗 突变型hDISC1前脑区诱导表达的小鼠模型。 我们假设，突变型hDISC1对神经元的影响的性质和大小将取决于突变型hDISC1在脑发育期间的表达时间，与出生后和/或成年期表达导致的更微妙的变化相比，在早期妊娠阶段的表达会导致更严重的异常。 具体目标1将对侧脑室、皮质和海马的体积、海马锥体神经元和海马齿状回颗粒细胞的树突树枝和棘密度以及海马齿状回的成体神经发生进行定量分析。 特异性目标2将评估内源性DISC1及其相互作用蛋白Lis1和Ndel1在hDISC1转基因小鼠中水平和分布的变化过程。 意义：这项应用有望促进我们对突变DISC1何时、何地以及如何影响神经发育与精神分裂症和情绪障碍的发病机制的理解。 一些重大的精神疾病被认为部分是由大脑发育的细微缺陷引起的，尤其是大脑皮层、海马体和其他前脑结构的发育(Weinberger，1996；Lewis，2002；Eastwood，2004；Arnold，2005)。精神疾病的神经发育起源的概念已经被广泛接受，尽管到目前为止证据主要是间接的(Marenco，2000)。直到最近，由于难以在大多数候选基因中确定明显的突变，致病机制的分析一直受到阻碍(Millar，2004；Mackie，2007)。最近对精神分裂症1(DISC1)基因的研究表明，它可以被用作研究精神分裂症和情绪障碍的模型(Ross，2006；Porteous，2006)。 我们已经证明，在转基因小鼠的前脑神经元中表达突变的人DISC1(HDISC1)会导致初级神经元中突起生长减弱、侧脑室轻度扩大以及类似于精神分裂症和相关疾病的某些特征的选择性行为改变(Ross，2006；Pletnikov，2008)。我们已经证明，突变的hDISC1的作用可能是通过它与内源性小鼠DISC1的结合和细胞分布的改变和/或内源性DISC1和参与神经发育的DISC1相互作用蛋白Lis1水平的降低来介导的(Gupta，2002)。这些发现提出了突变DISC1效应的显性-负性机制(Pletnikov，2007,2008)。类似的结果在转基因小鼠模型中也得到了证实，这些转基因小鼠的构成表达突变的hDISC1、截短的小鼠DISC1或该基因的C末端片段在出生后可诱导表达(Hiysta，2007；U，2007；Shenin，2008)。由于缺失的C末端片段不是已知的人类DISC1变异的直接类似物，并且只能在出生后短时间内表达，因此上述模型不能解决关于出生前和出生后表达的影响、短期表达和长期表达的影响或可逆表达的影响的关键问题。我们建议使用我们基于Tet-Off系统的突变型hDISC1可诱导表达模型来确定突变型hDISC1神经行为效应的时间窗口以及这些效应的潜在分子机制。这一方法有望为异常大脑和行为发育导致精神疾病的分子基础提供有价值的见解，并将更多地揭示精神分裂症和情绪障碍的关键时间窗口。 我们假设突变型hDISC1的分子和神经元效应的性质和大小将取决于突变型hDISC1在脑发育过程中的表达时间。我们预测，突变DISC1的早期效应可能会导致更严重的神经发育异常，而该蛋白出生后的早期或晚期效应可能会产生更微妙的大脑缺陷。我们假设突变的hDISC1通过改变内源性小鼠Dics1、Lis1和Ndel1的功能，通过显性-负性机制影响神经发育。

Schizophrenia is a devastating psychiatric illness arising in part from subtle defects in brain development. The Disrupted-ln-Schizophrenia-1 (DISC1) gene is an example of a strong candidate gene for studying the pathogenesis of schizophrenia and associated mental conditions with neurodevelopmental origin. A balanced translocation that segregates in a large Scottish pedigree with schizophrenia and other major mental illnesses causes a deletion of the DlSC1 gene, resulting in a truncated protein product that affects neurodevelopment. Despite of development of several DISC1 mouse models, the key questions regarding the timing of the prenatal vs. postnatal or lasting vs. reversible effects of mutant human (hDISC1) remained unanswered. We propose to identify the time windows of the effects of mutant hDISC1 by using our transgenic mouse model of inducible expression of mutant hDISC1 in forebrain areas. We hypothesize that the nature and magnitude of neuronal effects of mutant hDISC1 will depend on the time of expression of mutant hDISC1 during brain development, with more profound abnormalities resulting from expression during early gestation stages, compared to more subtle alterations resulting from expression during postnatal period and/or adulthood. Specific Aim 1 will perform quantitative analyses of the volumes of the lateral ventricles, cortex and hippocampus, dendrite arborization and spine density in pyramidal neurons of hippocampus and granule cells of the dentate gyrus of hippocampus as well as adult neurogenesis in the dentate gyrus of hippocampus. Specific Aim 2 will evaluate the time course of alterations in levels and distribution of endogenous Disc1 and Its interacting proteins, Lis1 and Ndel1, in hDISC1 transgenic mice. Significance: The application is anticipated to advance our understanding of when, where and how mutant DISC1 affects neurodevelopment with relevance to the pathogenesis of schizophrenia and mood disorders. Major mental illnesses have been suggested to arise in part from subtle defects in brain development, particularly development of the cerebral cortex, hippocampus and other forebrain structures (Weinberger, 1996; Lewis, 2002; Eastwood, 2004; Arnold, 2005). The concept of a neurodevelopmental origin of psychiatric diseases has received wide acceptance, although the evidence so far has been primarily indirect (Marenco, 2000). Until very recently an analysis of the pathogenic mechanisms has been impeded by a difficulty in identifying clear mutations in most candidate genes (Millar, 2004; Mackie, 2007). Recent studies of the Disrupted-In-Schizophrenia 1 (DISC1) gene indicate that It can be used as a model for studying aspects of schizophrenia and mood disorders (Ross, 2006; Porteous, 2006). We have demonstrated that expression of mutant human DISC1 (hDISC1) in forebrain neurons of transgenic mice leads to attenuated neurite outgrowth in primary neurons, mild enlargement of the lateral ventricles and selective behavioral alterations similar to some features of schizophrenia and related disorders (Ross, 2006; Pletnikov, 2008). We have shown that the effects of mutant hDISC1 may be mediated via its binding to endogenous mouse Disc1 and alterations in cellular distribution and/or decreased levels of endogenous Disc1 and Lis1, a DISC1 interacting protein involved in neurodevelopment (Gupta, 2002). These findings have suggested dominant-negative mechanisms of the mutant DISC1 effects (Pletnikov, 2007, 2008). Similar results have been demonstrated in transgenic mouse models with constitutive expression of mutant hDISC1, truncated mouse Disc1 or Inducible postnatal expression of a C-terminal fragment of the gene (Hikida, 2007; U, 2007; Shen, 2008). As the deleted C-terminal fragment is not a direct analog of a known variation of DISC1 in humans and can be expressed for a brief period of time during postnatal period only, key questions regarding effects of prenatal vs. postnatal expression or effects of short vs. long-lasting expression or effects of reversible expression cannot be addressed with the above models. We propose to use our model of inducible expression of mutant hDISC1 based on the Tet-off system to identify the time windows for the neurobehavioral effects of mutant hDISC1 and the underlying molecular mechanisms of those effects. This approach is expected to give valuable insights into the molecular underpinning of abnormal brain and behavior development to contribute to mental diseases and will shed more light on the critical time windows for schizophrenia and mood disorders. We hypothesize that the nature and magnitude of molecular and neuronal effects of mutant hDISC1 will depend on the time of expression of mutant hDISC1 during brain development. We predict that early effects of mutant DISC1 may lead to more profound neurodevelopmental abnormalities, whereas early or late postnatal effects of the protein could produce more subtle brain deficits. We hypothesize that mutant hDISC1 affects neurodevelopment via dominant-negative mechanisms by altering the functions of endogenous mouse Dics1, Lis1, and Ndel1.