A fundamental question in biology is how a single multipotential cell gives rise to cells of two or more distinct phenotypes. The blood system serves as a useful model to examine questions of cell fate determination. Most mature blood cells have a limited lifespan and therefore must be continuously replaced. This is achieved by hematopoietic stem cells, which have the capacity to both self-renew and undergo sequential commitment to at least ten different cell types. My laboratory is interested in further elucidating the molecular mechanisms that control these cell fate decisions. Prior work has shown that lineage-specific transcription factors play essential roles in this process1. Knock-out of these individual factors in mice leads to arrest in hematopoietic maturation at characteristic points along their developmental pathways. Importantly, many of these transcription factors are also the subject of viral insertions, chromosomal translocations, or mutations in various human leukemias and pre-leukemic syndromes2. This indicates that the dysregulation of normal hematopoietic transcriptional machinery plays a role in these hematologic malignancies. Further understanding of these normal processes may therefore provide important insights into the molecular pathophysiology of these disorders, and possibly new therapeutic approaches.
Current emphasis in my laboratory is on the development of megakaryocytes, large polyploid cells within the bone marrow that give rise to circulating platelets through an unusual process of cytoplasmic fragmentation. We are currently interested in how members of the GATA, FOG, RUNX and ETS families of transcription factors cooperate to specify and promote megakaryocytic differentiation, and how mutations within GATA-1 lead to megakaryoblastic leukemia in children with Down syndrome3-5. We have evidence that these factors participate in stable multiprotein complexes (with themselves and other proteins) within hematopoietic cells. We are utilizing a recently described technique for the metabolic biotinylation of proteins in living cells6. The tagged transcription factor-associated complexes are then purified using streptavidin-affinity chromatography, and associated proteins identified by mass spectrometry. Several novel factors have been isolated. Studies are underway to examine the functional significance of these factors using inducible lentiviral mediated RNAi and traditional mouse ES cell genetic knock-out technologies.
1. Cantor AB, Orkin SH. Hematopoietic development: a balancing act. Curr Opin Genet Dev. 2001;11:513-519.
2. Cantor AB, Orkin SH. Transcriptional regulation of erythropoiesis: an affair involving multiple partners. Oncogene. 2002;21:3368-3376.
3. Cantor AB, Katz SG, Orkin SH. Distinct domains of the GATA-1 cofactor FOG-1 differentially influence erythroid versus megakaryocytic maturation. Mol Cell Biol. 2002;22:4268-4279.
4. Chang AN, Cantor AB, Fujiwara Y, et al. GATA-factor dependence of the multitype zinc-finger protein FOG-1 for its essential role in megakaryopoiesis. Proc Natl Acad Sci U S A. 2002;99:9237-9242.
5. Gurbuxani S, Vyas P, Crispino JD. Recent insights into the mechanisms of myeloid leukemogenesis in Down syndrome. Blood. 2004;103:399-406.
6. Parrott MB, Barry MA. Metabolic biotinylation of recombinant proteins in mammalian cells and in mice. Mol Ther. 2000;1:96-104.