Our laboratory is interested in elucidating the basic cellular and molecular mechanisms implicated in cell fate choice and stem cell activity within tissues. We use the mouse as a model system. An important focus is on the control of nuclear function and structure including transcriptional networks, chromatin structure and dynamics, and DNA replication. Understanding how progenitor and differentiated cells function in normal tissue morphogenesis and homeostasis will reveal how deregulation of their precise control of growth and differentiation can lead to diseased tissues and cancer.
Our laboratory focuses on adult stem cells and their interaction with their tissue of residence, and uses the mouse skin as a primary model system to address the general questions outlined above. Within the skin epithelia stem cells are thought to reside both in the outer epidermis and in a specialized area of the hair follicle called the bulge. The bulge is a stem cell niche thought to keep their potent resident cells in a differentiation and proliferation inhibited state. It allows external signals to selectively penetrate and instruct stem cells to migrate out and proliferate when they are needed: during the initiation of the hair follicle growth and in wounded, regenerating skin. The bulge area is marked by a profoundly quiescent population of cells, known to incorporate BrdU (bromodeoxyuridine) label in the newly synthesized DNA and retain this label preferentially relative to other cells in the skin, for extended periods of time during the animal adult life. These label retaining cells (LRCs) have been attributed stem cell potential for more than 20 years, not only in the hair follicle, but also in other tissues where they have been identified.
We have devised a novel technique to isolate LRCs from tissues based on their GFP retention. A pulse and chase with histone H2B fused with GFP, with expression regulated by the tetracycline inducible system, allowed us to label and isolate live LRCs from the hair follicle bulge. Using a genomic approach a large number of factors preferentially expressed in bulge cells were identified. A significant fraction of these factors were likely involved in the cross-talk between bulge cells and the surrounding environment, suggesting a possible role for LRCs in organizing the stem cell niche.
We are currently trying to define:
- What factors regulate the specialized program of transcriptional activity in the bulge?
- How do factors expressed by bulge cells control stem cell activation and maintenance?
- What distinguishes LRCs from other cells within the hair follicle and what is their relationship with the stem cell niche?
- Do LRCs have special mechanisms to control their nuclear functions, and how does that impact their role within tissues?
We use a variety of molecular, biochemical, and tissue culture techniques, in vivo imaging and fluorescence activated cell sorting, as well as mouse transgenic and gene targeting (knock-out) technology to address these various questions.
Belmont, A. S., S. Dietzel, A. C. Nye, Y.G. Strukov, and T. Tumbar (1999) "Large-scale chromatin structure and function." Curr Opin in Cell Biol 11 (3): 307-311 [Review]
Tumbar, T., G. Sudlow, and A.S. Belmont (1999) "Large-scale chromatin unfolding and remodeling induced by VP16 acidic activation domain." J Cell Biol 145 (7): 1341-1354
Mahy, N. W. Bickmore, T. Tumbar, and A.S. Belmont (2000) "Linking large-scale chromatin structure with nuclear function" in Chromatin Structure and Gene Expression, Oxford University Press: 300-321 [Book Chapter]
Tsukamoto, T., N. Hashiguchi, S.Janicki, T. Tumbar, A.S. Belmont, and D. Spector (2000) "Visualization of gene activity in living cells." Nat Cell Biol 2 (12): 871-878
Tumbar, T. and A.S. Belmont (2001) "Interphase movements of a DNA chromosome region modulated by VP16 transcriptional activator." Nat Cell Biol 3 February: 134-139
Tumbar, T., G. Guasch, V. Greco, C. Blanpain, W.E. Lowry, M. Rendl, E. Fuchs (2003) "Defining the ephitelial stem cell niche in skin." Science 2004 Jan 16 303(5656): 359-63. Epub 2003 Dec 11
Fuchs E, Tumbar T, Guasch G. (2004) "Socializing with the neighbors: stem cells and their niche." Cell 116(6): 769-78
Tumbar, T. and E. Fuchs (2004) "Epithelial skin stem cells" in Handbook of Adult and Fetal Stem Cells, Academic Press [Book Chapter]
Tumbar, T. (2006), "Epithelial skin stem cells." Methods in Enzymology 419: 73-99
Osorio, K. M., Lee, S. E., McDermitt, D. J., Waghmare, S. K., Zhang, Y.V., Woo, H. N., and T. Tumbar, (2008) "Acute myeloid leukemia factor 1 controls developmental but not injury driven activation of hair follicle stem cells." Development 135: 1059-1068
Waghmare, S. K., Bansal, R., Lee, J., Zhang, Y. V., McDermitt, D. J., and T. Tumbar (2008) "Quantitative proliferation dynamics and random chromosome segregation of hair follicle stem cells." EMBO J. 27(9): 1309-20. Epub 2008 Apr 10
Ying V. Zhang, Janice Cheong, Nichita Ciapurin, David J. McDermitt and Tudorita Tumbar (2009) "Distinct self-renewal and differentiation phases in the niche of infrequently dividing hair follicle stem cells." Cell Stem Cell, doi:10.1016, Epub Aug 6
Hoi, C.S., Lee, S.E., Lu, SY., McDermitt D.J., Osorio, K.M., Piskun C.M., Peters R.M., Paus R, and T.Tumbar (2010) "Runx1 directly promotes proliferation of hair folicle stem cells and epithelial tumor formation in mouse skin." Mol Cel Bio, Mar 22. [Epub ahead of print]
Zhang, Y.V., White, B., Shalloway, D. and T.Tumbar (2010) "Stem cell dynamics in mouse hair follicles: a story from cell division counting and single cell lineage tracing." Cell Cycle April 19; 9(8). [Epub ahead of print] doi:10.1242/dev.012799
Hoi, C.S., Lee, S.E., Lu, SY., McDermitt D.J, Osorio, K.M., Piskun C.M., Peters R.M., Paus R, and T. Tumbar (2010) “Runx1 directly promotes proliferation of hair follicle stem cells and epithelial tumor formation in mouse skin.” Mol Cell Biol 30 (10): 2518-36. Epub 2010 Mar 22
Osorio, KM., Lilja KC., and Tumbar, T. (2011) “Runx1 modulates adult hair follicle stem cell emergence and maintenance from distinct embryonic skin compartments.” J Cell Biol 193 (1): 235-50 [Cover Image]