Timothy P. Bender, PhD
Lymphocyte development and the regulation of gene expression during hematopoiesis
The general interest in the Bender laboratory is lymphocyte development and the regulation of gene expression during hematopoiesis. For some time, the lab has focused their attention on the biology of the Myb family of transcription factors and their role in regulating hematopoietic maturation. The Myb protooncogene is the founding member of the Myb family and encodes a highly conserved transcription factor that is abundantly expressed in immature hematopoietic cells and expression is down regulated during the maturation of each hematopoietic lineage. Interestingly, they have demonstrated that the regulation of Myb expression switches in both B and T lymphocytes from constitutive at the immature stages of lymphocyte development to cell cycle regulated expression in mature lymphocytes. Despite the interesting pattern of Myb expression during hematopoiesis little is understood about the role(s) played by c-Myb during hematopoietic maturation due the embryonic lethality of traditional Myb null mutations. They have recently made and started to characterize Cre/loxP based conditional Myb mutations in mice that allow them to ablate c-Myb expression either specifically during B or T cell development or inducibly in mature cells. Using these mice they have found that c-Myb is required for both T and B cell maturation in the primary lymphoid organs. During T cell development, they have identified roles for c-Myb at three critical checkpoints: differentiation from DN to DP thymocytes, survival of preselection DP thymocytes and differentiation to the CD4 SP stage. In particular, they have identified roles for c-Myb in regulating the efficiency of V(D)J recombination at the Tcrb locus and the process of b-selection. During B cell development they have identified a crucial requirement for c-Myb during transition from the pro-B to the pre-B cell stage of differentiation. Most recently, they have identified a role for c-Myb in regulating the peripheral B cell response to BAFF, which is a major mediator of B cell homeostasis. It will now be crucial to identify direct targets of c-Myb activity during the early stages of T and B cell development. Their current focus is to understand the relationship between c-Myb activity and the regulation of accessibility of the Tcrb locus to V(D)J recombinase as well as the regulation of lymphocyte survival. The floxed Myb mice provide a previously unavailable, physiologically relevant model to understand the relationship between Myb, cell survival, proliferation and differentiation. In addition, they are developing mice that allow conditional over expression of c-Myb, or other Myb family members, based on the Cre/loxP approach. Again, models for expression of Myb family members have been notoriously difficult to establish, most likely because widespread deregulated expression of these proteins is lethal. Their models will provide an opportunity to assess the importance of deregulated c-Myb expression to the development of leukemia and lymphoma as well as cancer of the breast, lung and colon.
Their work would not be possible without the FACS core. This group provides essential services that move well beyond providing well-maintained flow cytometers and a cell sorter and include advice in the application of flow cytometry, the planning of experiments and the introduction of new technology. Also, as they move into the use of microchip gene arrays, the MicroArray lab in the Biomedical Research Facility will become a very important resource for them both in terms of carrying out probe preparation and hybridization to gene chips but also for preliminary analysis.
They have a long-standing collaboration with Kodi Ravichandran that has included the development and characterization of conditional mouse models that allow the characterization of Shc function. They jointly published a major paper that clearly identified a role for Shc in signaling through the pre-TCR. In return, Ravichandran is a crucial collaborator on their grants where he provides much needed expertise in analysis of signaling pathways. Their interactions extend to joint publications and co-investigator status on several grants.
Dr. Bender is involved in collaborations with Drs. Michael Smith to develop models for tissue specific ablation of gene expression in gastric tissue and Timothy Bullock to develop conditional models to ablate CD70 expression in antigen presenting cells. To date these interactions have led to NIH level funding and serves as a co investigator on grants from both labs. No publications have come from this work so far.
Dr. Bender also provides significant input, or has provided significant input and advice, into the development of mouse models with Drs. JT Parsons, SJ Parsons, Adam Goldfarb, Deb Lannigan, Mitch Smith and Amy Bouton. Finally, Dr. Bender has just submitted a new proposal to the NIH that includes a component to use gene arrays to identify targets of c-Myb activity. This grant includes Jai Lee as a collaborator and a 5% effort commitment as well as significant interaction, with Todd Stukenberg to look at mitosis in c-Myb deficient thymocytes and David Mullins to make hybridization probes for gene microarays from very small numbers of electronically sorted cells.