TRANSCRIPTIONAL MECHANISMS REGULATING ACTIVITY DEPENDENT GENE EXPRESSION

在发育过程中用于重塑神经系统和骨骼肌的活动依赖性过程需要将突触信号耦合到基因表达的选择性变化。这种类型的调节被称为“活性-转录偶联”。我们已经使用了NMDA受体在大脑中的调节和编码收缩蛋白在肌肉中的基因，作为活性-转录偶联的模型。我们以前证明，在小脑中的NMDA受体（NR）的NR 2C亚基的表达需要神经活动，以及称为neuregulin的营养因子。在目前的研究中，我们提供的证据表明，通过这两个受体的共同信号可能发生在突触。我们发现，NMDA和ErbB受体富集在突触后密度（PSD），在那里他们与相同的蛋白质窝藏PDZ蛋白质-蛋白质相互作用域相互作用。PDZ结构域蛋白是重要的，因为它们支架受体和通道的信号分子，从而耦合突触活动的信号级联在突触后神经元。我们还开始表征在发育过程中调节受体NR 2A亚基和响应神经活动的DNA调节序列。肌肉的慢缩和快缩特性由来自运动神经元的细胞谱系和表观遗传信号决定，运动神经元选择性地调节收缩基因的转录。为了了解选择性调节不同肌肉基因的信号传导途径，我们已经确定并表征了肌钙蛋白I慢（TnIs）和快（TnIs）基因的增强子。 我们的研究结果表明，一个复杂的转录因子与这些增强子相互作用，以调节转录。使用酵母-1-杂交系统，我们已经分离出假定的因素，赋予肌纤维型特异性。这些因子之一，称为GTF-3，编码一种具有5-6个内部重复序列的蛋白质，其可以与一系列转录因子相互作用。有趣的是，GTF-3基因以及该基因家族的另一个成员在患有Williams-Beuren综合征（WBS）的人中被删除，该综合征是由染色体7q11.23上的微缺失引起的。据报道，WBS患者有不同程度的智力低下、主动脉瓣上狭窄和肌病。研究正在进行中，以了解GTF-3在与WBS相关的缺陷中的作用。

The activity-dependent processes that serve to remodel the nervous system and skeletal muscles during development, require the coupling of synaptic signals to selective changes in gene expression. This type of regulation is referred to as "activity-transcription coupling". We have used the regulation of NMDA receptors in the brain and of the genes encoding contractile proteins in muscle, as models for activity-transcription coupling. We demonstrated previously that the expression of the NR2C subunit of the NMDA receptor (NR) in cerebellum requires neural activity, as well as a trophic factor known as neuregulin. In the present studies, we provide evidence that co-signaling via these 2 receptors may occur at synapses. We found that NMDA and ErbB receptors are enriched at postsynaptic densities (PSD) where they interact with the same proteins harboring PDZ protein-protein interaction domains. The PDZ-domain proteins are important because they scaffold receptors and channels to signaling molecules, thus coupling synaptic activity to signaling cascades in the postsynaptic neurons. We have also begun to characterize the DNA regulatory sequences that regulate the NR2A subunits of the receptor during development and in response to neural activity. The slow- and fast-twitch properties of muscles are determined by cell lineage and epigenetic signals derived from motoneurons, which selectively regulate the transcription of contractile genes. To understand the signaling pathways that selectively regulate distinct muscle genes, we have identified and characterized the enhancers of the troponin I slow (TnIs) and fast (TnIf) genes. Our results suggest that a complex of transcription factors interact with these enhancers to regulate transcription. Using a yeast-1-hybrid system, we have isolated putative factors that confer muscle fiber-type-specificity. One of these factors, known as GTF-3, encondes a protein with 5-6 internal repeats that may interact with a series of transcription factors. Interestingly, the GTF-3 gene, as well another member of this gene family, is deleted in persons afflicted with the Williams-Beuren Syndrome (WBS) which results from a micro-deletion on chromosome 7q11.23. Persons with WBS are reported to have variable degrees of mental retardation, supra valvular aortic stenosis, and myopathies. Studies are in progress to understand the role of GTF-3 in the deficiencies associated with WBS.