Gregg G Gundersen
Departments of Pathology & Cell Biology
Research in my laboratory is focused on the fundamental question of how cells generate cellular asymmetry to carryout
their specific function. Elements of the cytoskeleton, known as microtubules, have been found to play a central role
in this process.
We utilize motile fibroblasts as a model system to study how microtubules contribute to cell polarity. In these cells
there are two sources of microtubule polarity: the selective stabilization of microtubules oriented towards the leading
edge, and the reorientation of microtubule organizing center (MTOC) towards the leading edge. We are currently
investigating how the polarization of the microtubule array is signaled in the cytoplasm, and how the polarization of
the microtubule array contributes to other cell polarity processes. We employ biochemical, molecular and cell biological
approaches to address these questions, including real time microscopic observation of the behavior of fluorescent
molecules introduced into cells by microinjection or by transfection.
Wounded Monolayer System
Stable post-translationaly modified MTs shown in green, MTOC shown in red. Fibroblasts are grown until they form a
confluent monolayer then serum starved for two days. Serum-starved cells are unable to polarize their cytoskeleton
in response to wounding. Addition of serum triggers polarization of the microtubules in two ways: stable MTs are formed
and oriented towards the wound edge, and the MTOC is reoriented so that it lies between the nucleus and the wound edge.
The stabilization of microtubules in specific locations in cells is central to the idea that microtubules drive cellular
polarization. We have developed a serum starved fibroblast system to identify extracellular factors and intracellular
signal transduction pathways involved in triggering microtubule stabilization in crawling fibroblasts. We have used this
system to show that the small GTP-binding protein, Rho, a member of the ras superfamily, is critically involved in the
selective stabilization of microtubules in the lamella of crawling cells. Recently we identified the mDia, a member of
the formin family of proteins, as the downstream target of Rho that mediates MT stabilization. In budding yeast formins
have been genetically implicated in the capture and shrinkage of the plus end of microtubules in the cortex of the bud.
We are currently testing whether other proteins from the "capture shrinkage pathway" (i.e. EB1 and APC) are involved in
microtubule stabilization in fibroblasts.
The subunit protein of microtubules, tubulin, undergoes a unique post translation modification, known as detyrosination,
when microtubules are stabilized. We have recently found that detyrosination acts as a signal for the interaction of stable
microtubules with other organelles in the cell. Thus, detyrosinated microtubules act as preferential sites for the
establishment of an extended array of vimentin intermediate filaments in fibroblasts. In addition, detyrosinated microtubules
are preferentially used for export from the endocytic recycling compartment while tyrosinated microtubules are are
preferentially used for import from the plasma membrane to this compartment. Other cellular organelles, e.g., mitochondria and
endoplasmic reticulum, may also be dependent on detyrosinated microtubules. With these results, we are now able to suggest a
general mechanism for how cells establish internal organization: 1) dynamic microtubules are locally stabilized 2) the stable
microtubules are post-translationally modified, and 3) the modified microtubules interact with other cellular organelles.
Recently we used the serum starved fibroblast system to show that MTOC reorientation is regulated by a specific signal
transduction pathway. Similar to the microtubule stabilization pathway, MTOC reorientation is triggered by a small G-protein,
CDC42. By activating MTOC orientation with serum factors or active CDC42 we have been able to determine that dynein and the
dynactin complex act downstream of CDC42 to provide the force required to reposition the MTOC in response to extracellular
cues. Importantly we have shown that MTOC reorientation and selective stabilization of microtubules towards the cell edge
are each controlled by distinct and independent signaling pathways despite the fact that these two polarization events act
to rearrange a single microtubule array.
In the final project in the laboratory, we have begun to analyze the relationship between adhesion and microtubules. We plan
to address two questions: how adhesion affect the microtubule stabilization pathway, and how microtubule dynamics affect focal
- Gundersen, G.G. Evolutionary Conservation of Microtubule Capture Mechanisms. Nature Rev. Mol. Cell Biol., In Press.
- Lin, S.X., Gundersen, G.G. & Maxfield, F.R. 2002. Exit from the endocytic recycling compartment to cell surface depends on stable, detyrosinated (Glu) microtubules and kinesin. Mol. Biol. Cell 13: 96-109. 50. Gundersen, G.G. 2002.
- Palazzo, A.F., Joseph, H. L., Chen, Y.-J., Alberts, A. S., Pfister, K. K., Dujardin, D. L., Vallee, R. B. & Gundersen, G. G. 2001. CDC42, dynein and dynactin regulate MTOC reorientation independent of Rho regulated microtubule stabilization. Curr. Biol. 11:1536-1541 (2001).
- Palazzo, A.F., Cook, T.A., Alberts, A.S. & Gundersen, G.G. 2001. mDia regulates the formation and orientation of stable microtubules. Nature Cell Biol. 3: 723-729 (2001).
- Infante, A, Stein, M., Zhai, Y., Borisy, G.G. & Gundersen, G.G. 2000. Detyrosinated (Glu) MTs are stabilized by an ATP-sensitive plus-end cap. J. Cell Sci., 113: 3907-3919 (2000).
- Liao, G., Kreitzer, G., Cook, T.A. & Gundersen, G.G. A Rho-dependent signal transduction pathway that regulates microtubule stability, tubulin deytosination & intermediate filament location. FASEB J. 13: S257-S260 (1999).
- Smilenov, L., Mikhailov, A., Pelman, R., J. Marcantonio, E.E. & Gundersen, G.G. Focal adhesion motility revealed in stationary fibroblasts. Science 286: 1172-1174 (1999).
- Martys, J. L., Ho, C.-L., Liem, R.K.H. & Gundersen, G.G. 1999. IFs in motion: Observations of intermediate filaments in cells using GFP-vimentin. Mol. Biol. Cell 10: 1289-1295 (1999).
- Kreitzer, G., Liao, G. & Gundersen, G.G. Detyrosination of tubulin regulates the interaction of intermediate filaments with microtubules in vivo through a kinesin-dependent mechanism. Mol. Biol. Cell 10: 1105-1118 (1999).
- Gundersen, G.G. & Cook, T.A. Microtubules and signal transduction. Curr. Opin. Cell Bol. 11: 81-94 (1999).
- Cook, T.A., Nagasaki, T., and Gundersen, G.G. Rho GTPase mediates the selective stabilization of microtubules in vivo. J. Cell Biol. 141: 175-185 (1998).
- Liao, G., and Gundersen, G.G. Kinesin is a candidate for crossbridging microtubule and intermediate filaments: selective binding of kenesin to detyrosinated tubulin and vimentin. J. Biol. Chem. 273: 9797-9803 (1998).
- Mikhailov, A. & Gundersen, G.G. Direct imaging of microtubule behavior in locomoting fibroblasts treated with nocodazole or taxol reveals a relationship between microtubule dynamics and lamellipodia formation. Cell Motil. Cytoskel. 41: 325-340 (1998).
- Ho, C.-L., Martys, J.L., Mikhailov, A., Guncersen, G.G., and Liem, R.K.H. Novel features of intermediate filament dynamics revealed by green fluorescent protein fusion proteins. J. Cell Sci. 111: 1767-1778 (1998).