The long-term goal of this project is to understand the signaling mechanisms underlying synapse development. Using powerful strategies at the Drosophila larval neuromuscular junction (NMJ) we have uncovered a non-canonical Wnt signaling pathway, the Frizzled Nuclear Import (FNI) pathway, which is required for proper synapse development. During the last funding cycle, we found that the FNI pathway is associated with the formation and nuclear egress of large ribonucleoprotein granules (megaRNPs) containing synapse-specific mRNAs. In this pathway, endogenous transcripts are packaged in megaRNP granules within the nucleus and are then exported to the cytoplasm by budding through the nuclear membrane in a process akin to the nuclear egress of Herpes-type viruses. The approach in this application constitutes an incisive strategy to elucidate the molecular machinery underlying this novel mode of nuclear export. In the same manner by which uncovering molecular components of the nuclear pore complex has led to major progress in understanding regulation of transcription, RNA processing and translation, we expect that unraveling constituents of nuclear envelope budding will shed important and novel perspectives on these processes. Our preliminary studies identify Torsin, a AAA-ATPase, which in humans is linked to early onset dystonia as a key element in the remodeling of nuclear membranes required for budding. We have also identified components of the cell polarity complex (atypical Protein Kinase C, Par3/Bazooka and Dap160/Intersectin) as important determinants of local remodeling of the nuclear lamina during nuclear megaRNP egress. In this project we propose a comprehensive strategy to uncover other components of the budding machinery and to determine their impact on synapse development and function.
The specific aims of this project are (1) to identify the molecular linchpins of nuclear megaRNP export by nuclear envelope budding, (2) test the hypothesis that Torsin is required for budding at the INM and to determine its role in NMJ development, and (3) test the hypothesis that Dap160, Baz and Par6 regulate aPKC-dependent local remodeling of the nuclear lamina to enable nuclear envelope budding of megaRNPs. By providing novel insight into the mechanistic basis of such diseases as nuclear envelope- associated dystrophies (e.g., laminopathies and envelopathies), HSV-type infections and dystonia, we expect our studies to open new windows for the design of therapies to treat or cure these conditions.
We have discovered a previously unrecognized pathway for the export of cellular mRNAs, which we propose to investigate. This pathway, wherein mRNAs exit the nucleus by modification of nuclear envelope membranes, resembles the mechanism utilized by herpes-type viruses to exit the nucleus. The studies proposed in this project will have foundational impact for human health by providing knowledge and potential pharmacological targets to treat many diseases associated with the nuclear envelope, including laminopathies, such as Emery-Dreyfus muscular dystrophy and progeria, movement disorders such as dystonia, and herpes-type infections such as shingles and genital herpes.
|Fradkin, Lee G; Budnik, Vivian (2016) This bud's for you: mechanisms of cellular nucleocytoplasmic trafficking via nuclear envelope budding. Curr Opin Cell Biol 41:125-31|