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Katharine S. Ullman

Associate Professor of Oncological Sciences and of Biochemistry

B.A. Northwestern University

Ph.D. Stanford University

Research

References

katie.ullman@hci.utah.edu

Katie Ullman's Lab Page

Research

The nucleus and cytoplasm of a eukaryotic cell provide unique environments for specialized processes.  Moreover, this physical division adds a critical level of spatial regulation to many fundamental cellular functions, from DNA replication to translation.  Bothseparationandcommunication between these distinct compartments are vital to normal cell function.  Two membrane bilayers form a nuclear envelope that provides a barrier; nuclear pore complexes embedded in this envelope allow for selective trafficking between the nucleus and cytoplasm.  Two main goals of my laboratory are to understand molecular mechanisms that guide nucleocytoplasmic transport and to decipher the process by which the nuclear pore and the nuclear envelope itself are disassembled in a regulated manner at mitosis. 

The nuclear pore complex is a huge macromolecular structure (120 MDa in vertebrates).  Although several individual components of the nuclear pore have been identified at a molecular level, a major challenge in the field is to understand how these components cooperate to direct regulated, bi-directional movement of cargo.  Each pore is estimated to guide the transport of over 100 molecules per minute.  Yet, despite the “high through-put” nature of this process, transport occurs with specificity.  We are focused on learning what comprises the export machinery of a cell and deciphering how this apparatus accomplishes the task of export. 

Some of our efforts are concentrated on Nup153, a modular pore protein with multiple roles in nucleocytoplasmic transport.  Having established that Nup153 plays a critical role in specific types of RNA and protein export, we are now defining the functional domains within Nup153 and how each of these contributes to the transport of different cargo.  This approach led us to the identification of a novel RNA binding domain within Nup153 and to current work aimed at deciphering how this interaction fits into the coordinated events that lead to mRNA transport to the cytoplasm. 

When a cell divides, nuclei undergo dramatic remodeling.  In most cases, the nuclear envelope is disassembled.  This breakdown process involves dispersal of the nuclear membrane as well as solubilization of nuclear pore complexes, which break into small subunits. My laboratory is interested in elucidating how the nuclear envelope gets remodeled during each cell cycle.  We have discovered an early role for specific nuclear pore proteins in recruiting “breakdown machinery” to the nuclear envelope and we are currently trying to understand this in greater mechanistic detail.  With new insight into players involved in nuclear disassembly, we are also interested in 1) learning how mitotic signaling events regulate nuclear remodeling and 2) targeting a step in nuclear envelope breakdown to arrest cell proliferation.

 

Panel A. These are oocytes injected with red fluorescent dextran into the nucleus and green fluorescent dextran into the cytoplasm.  The oocyte on the left has an intact nuclear envelope, whereas nuclear envelope breakdown has initiated in the oocyte at right. [Suzanne Elgort]
Panel B.  These are nuclei assembled in a cell-free system and incubated with a red fluorescent protein that is imported through the newly formed nuclear pores (membranes are stained green, DNA is stained blue). [Jin Liu] 
Panel C. This is the nucleus of a cultured human cell, where nuclear pores (red) and COPI membrane remodeling machinery (green) are being monitored as the cell progresses into mitosis. [Amy Prunuske; note: the panels are not shown at the same scale]

References