Cellular mechanisms of nucleocytoplasmic export through Nuclear Envelope Budding

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PROJECT SUMMARY/ABSTRACT Transport of nucleic acids and proteins from the nucleus to the cytoplasm is essential for nearly all cellular processes, and when mis-regulated, is associated with diseases, tumor formation/growth, and cancer progression. Canonically, this indispensable process has been thought to occur exclusively via Nuclear Pore Complexes, which span the nuclear envelope’s double membranes and provide a critical regulatory step in what exits (and enters) the nucleus. Recently, Nuclear Envelope (NE-) budding was shown to provide an alternative pathway for nuclear exit, particularly for large ribonucleoprotein (RNP) complexes that would otherwise need to unfold/remodel to fit through the pores. In this pathway, large macromolecule complexes are encapsulated by the inner nuclear membrane, cross the perinuclear space, fuse with the outer nuclear membrane, and are released into the cytoplasm, a mechanism strikingly similar to herpesvirus nuclear egress. Thus, NE-budding elegantly allows for large RNP complexes to exit the nucleus together and be delivered as a package for specific cellular functions. Despite its clear biological importance and clinical relevance, very little is yet known about the regulatory or structural machineries that allow NE-budding to occur in any system. Recently, we found that the Wiskott Aldrich Syndrome family actin nucleation protein, WASH, its four subunit regulatory complex (SHRC), and Arp2/3 are necessary for NE-budding. Using WASH/SHRC as a new entry point, in tandem with strategies to discover novel genes/proteins involved in this process, our long-term goal is to understand the molecular and cellular mechanics that govern NE-budding. The specific aims of this proposal are to determine the mechanism(s) of WASH/SHRC function in NE-budding, and to identify/analyze the infrastructural components/machineries governing the dynamic NE-budding process using a combination of genetic, biochemical, cell biological, time-lapse live imaging, and super- resolution/EM microscopy approaches. Drosophila provides an excellent, genetically amenable, organism for studying this conserved process due to its amenability for imaging and the wealth of cutting edge cell/molecular techniques and reagents. The information gathered in these studies will help to elucidate the mechanisms governing this exciting new nuclear export pathway in normal development or when mis-regulated in disease conditions, and may inform the study of herpesvirus nuclear egress as well.