Signal Transduction Pathways Regulating Neuron Differentiation

描述(申请人提供)：拟议研究的长期目标是阐明调节神经元分化的信号和转录机制。我们最近发现，转录因子肌细胞增强因子2A(MEF2A)促进哺乳动物大脑中分化神经元突触后树突状细胞的形态发生。在发育中的哺乳动物小脑中，颗粒神经元分化的最终结果是树突爪的产生，苔藓纤维和高尔基体神经元轴突在树突爪上形成联系。RNAi在小脑片和出生后大鼠小脑体内对MEF2A的基因敲除揭示了MEF2A在突触后树突状细胞爪分化中的重要作用。一种转录抑制形式的MEF2A在Lys403处被求和，促进树突状爪子的分化。这些发现提出了几个基本的问题，即SUMO化的MEF2A的新功能是如何在神经元中调节的，以及SUMO化的MEF2A如何协调突触后树突状细胞的分化。为了解决这些问题，我们建议确定刺激MEF2A相加基化的酶，从而促进树突状爪状分化。使用候选的和无偏倚的方法，我们还将确定被相加的MEF2A的基因靶点，这些基因靶点介导其促进突触后分化的能力。最后，我们将表征钙/钙调神经磷酸酶-MEF2A信号通路的发育作用，该信号通路抑制MEF2A总甲基化，从而抑制树突状爪子的形态发生。这项拟议的研究代表了一系列重要的实验，这些实验应该解决我们在理解神经元分化背后的信号和细胞内在转录机制方面的一个主要差距。此外，由于突触后树突状病理被认为与包括神经退行性疾病和智力低下在内的各种神经和精神障碍的发病机制有关，因此拟议的研究应该为更好地了解这些疾病提供基础。

DESCRIPTION (provided by applicant): The long-term goals of the proposed research are to elucidate the signaling and transcriptional mechanisms regulating neuronal differentiation. We recently discovered that the transcription factor myocyte enhancer factor 2A (MEF2A) promotes postsynaptic dendritic morphogenesis in differentiating neurons in the mammalian brain. In the developing mammalian cerebellum, granule neuron differentiation culminates in the generation of dendritic claws upon which mossy fibers and Golgi neuron axons form connections. Genetic knockdown of MEF2A by RNAi in cerebellar slices and in in vivo in the postnatal rat cerebellum revealed an essential function for MEF2A in postsynaptic dendritic claw differentiation. A transcriptional repressive form of MEF2A that is sumoylated at Lys403 promotes the differentiation of dendritic claws. These findings have raised several fundamental questions on how the novel function of sumoylated MEF2A is regulated in neurons and how sumoylated MEF2A orchestrates postsynaptic dendritic differentiation. To address these questions, we propose to identify the enzyme that stimulates the sumoylation of MEF2A and thereby promotes dendritic claw differentiation. Using candidate and non-biased approaches, we will also identify the gene targets of sumoylated MEF2A that mediate its ability to promote postsynaptic differentiation. Finally, we will characterize the developmental role of a calcium/calcineurin-MEF2A signaling pathway that suppresses MEF2A sumoylation and thereby inhibits dendritic claw morphogenesis. The proposed research represents an important set of experiments that should address a major gap in our understanding of the signaling and cell-intrinsic transcriptional mechanisms that underlie neuronal differentiation. In addition, since postsynaptic dendritic pathology is thought to contribute to the pathogenesis of diverse neurologic and psychiatric disorders, including neurodegenerative diseases and mental retardation, the proposed research should provide the foundation for a better understanding of these disorders.