The major goal of this project is to understand the mechanisms by which the postsynaptic apparatus is laid down and remodeled during synapse development and plasticity. In addition, a major goal is to expand my training, gain new skills, and acquire a rich foundation upon which I will build my own independent lab. A central question in neuroscience regards the mechanisms by which gene expression is regulated during synapse development and plasticity. Emerging research suggests that Wnt signaling plays fundamental roles in synapse development and function and is at the cross-road of devastating nervous system diseases. Studies in my lab have discovered a non-canonical Wnt signaling pathway, the Frizzled Nuclear Import (FNI) pathway, which is essential for the formation and modification of the postsynaptic apparatus at the developing neuromuscular junction in Drosophila. Upon signaling by the Wnt Wingless (Wg), the Wnt receptor, dFrizzled 2 (DFz2) is internalized, cleaved, and the resulting C-terminal fragment (DFz2C) translocates to the nucleus. In the nucleus, DFz2C localizes to prominent foci at the periphery of muscle nuclei, which associate with large ribonucleoprotein (RNP) granules. These RNP granules contain synapse-specific mRNA transcripts and their formation is regulated by synaptic activity. Unexpectedly, these granules exit the nucleus in a manner independent of nuclear pore complexes, by budding directly through the nuclear envelope, a process thought to be exclusive for the nuclear egress of Herpes nucleocapsids. These findings suggest a novel nuclear export mechanism challenging a major dogma in cellular biology. The goal of this project is to determine the mechanism by which these RNP granules escape the nucleus by nuclear envelope budding and to understand its impact during synapse development.
The specific aims of this project are (1) To test the hypothesis that Dap160, a dynamin and atypical PKC binding protein, mediates nuclear envelope budding of DFz2C-RNPs and that its function is required for normal development and function of the NMJ. (2) To carry out a RNAi screen searching for components mediating nuclear envelope budding. These studies are expected to be highly significant in our understanding of synapse development, cellular biology, and human health. They will provide fundamental information on how Wnt signaling links synapse development to regulation of mRNAs, they will substantiate a novel mechanisms of nuclear export, and they will advance our ability to treat diseases of the nuclear envelope, such as Laminopathies, and Herpes infections such as Shingles, which remain dormant in the nervous system before becoming active.
The findings in this project will elucidate pathogenic mechanisms for diseases associated with the nuclear envelope, including muscular dystrophies and premature aging. Additionally, these results will further our understanding of herpes viral infections, and identify targets for novel therapeutic interventions to treat these infections.