MOLECULAR MECHANISMS MEDIATING NEURONAL PLASTICITY.

点击翻译按钮获取中文摘要

SPECIFIC AIMS Advances in understanding the molecular mechanisms mediating neuronal plasticity have provided important clues to the pathophysiology of drug abuse and addiction. Although substantial progress has been made in elucidating several key aspects of this process, e.g. the role of NMDA and AMPA receptors in mediating the induction and expression of activity-induced plasticity, respectively, critical features of this process are only partially understood. For example, it is now clear that enduring forms of synaptic plasticity require local translation of mRNAs that have been pre-positioned in the vicinity of synapses. However, we are only beginning to understand the mechanisms and molecules mediating mRNA trafficking and translation. In addition, recent studies have focused attention on the prevalence and importance of morphological changes associated with synaptic plasticity. However, how these changes occur and their relevance to functional plasticity are poorly defined. Accordingly, there is intense interest in understanding the molecular machinery that mediates and regulates these processes. To gain insights into these key features of synaptic plasticity, we plan to focus on two projects. In one, we will investigate the function and regulation of Tech, a RhoA GEF enriched in brain that has been implicated in regulating dendritic morphology. In the other, we will examine the role of the Translin/Trax RNA binding complex in mediating RNA trafficking in dendrites.. Tech: a neuronal RhoA GEF Recent studies have demonstrated that the Rho family of small GTPases controls a versatile network of intracellular signaling pathways that play a pivotal role in regulating neuronal morphology and synaptic plasticity. The importance of this signaling pathway in synaptic plasticity has been underscored by the finding that abnormalities in Rho signaling pathways lead to mental retardation. Furthermore, its relevance to drug abuse has been supported by recent studies linking changes in the activity of LIM kinase and its substrate cofilin, two downstream effectors of the Rho signaling pathway, to long-term effects of cocaine. To help define the regulation and role of the Rho signaling pathway in neurons, we have begun to characterize a RhoA GEF, called Tech, that is highly enriched in brain. In preliminary studies, we have found that overexpression of Tech constructs in cultured neurons triggers prominent effects on dendritic morphology and also reduces the level of surface GluR1 staining. In studies aimed at understanding how Tech is regulated, we have found that, like other RhoGEF family members, it contains an autoinhibitory domain. Furthermore, our recent findings suggest that Tech undergoes tyrosine phosphorylation at a site within this domain. Accordingly, we plan to: I. Examine the impact of Tech deletion on neuronal morphology and AMPA receptor trafficking, and II. Test the hypothesis that Tech GEF activity is regulated by tyrosine phosphorylation. Translin/Trax RNA binding complex In previous studies, we have identified Translin and Trax as subunits of an RNA binding complex that has been implicated in mediating dendritic RNA trafficking. Compelling evidence supporting this hypothesis has emerged from recent studies conducted in collaboration with Dr. E. Tongiorgi. In brief, we have found that BDNF mRNA co-precipitates with the Translin/Trax complex and that Translin siRNA suppresses dendritic trafficking of BDNF mRNA in hippocampal cultures. As these findings have provided "proof of principle" that the Translin/Trax complex mediates dendritic trafficking of RNA, we plan to: I. Identify other transcripts that bind to the Translin/Trax complex in brain, and II. Assess the role of the Translin/Trax complex in regulating the localization of these transcripts.