David Ransom
Ph.D., University of Virginia, 1994
Assistant Professor, Cell and Developmental Biology
The specification of tissue-specific stem cells and the differentiation of stem cells into organs require the interaction of DNA-binding transcription factors with co-activators and co-repressors. The long term goal of our work is to better define how the TIF1 family of co-activators and co-repressors function in the development of a variety of stem cell populations that are derived from ventral mesoderm including hematopoietic stem cells that give rise to embryonic and adult blood cells and mesenchymal stem cells that give rise to connective tissue and smooth muscle cells.
We use the zebrafish as a genetic and developmental model system to identify the functions of genes that are essential for transcriptional regulation of hematopoietic and mesenchymal cell development. The zebrafish is an ideal system for vertebrate genetics and embryology given its small size, high fecundity and translucent embryos that develop outside the mother. Large numbers of zebrafish can be efficiently raised and analyzed in the state-of-the-art aquatic facility adjacent to my laboratory. We can rapidly test gene function by microinjecting mRNAs or antisense oligonucleotides into zebrafish and directly observing organogenesis in living embryos. We will also conduct forward genetic screens for mutations disrupting the differentiation of stem cells in ventral and lateral plate mesoderm.
We are currently working to elucidate the function of Transcriptional Intermediary Factor 1 gamma (TIF1gamma) and its associated transcription factors in hematopoiesis. . As part of a large-scale forward genetic screen, we previously identified bloodless zebrafish mutants that failed to express GATA-1 in embryonic hematopoietic precursors (Ransom et al., 1996). We named one of these zebrafish genes moonshine. We positional cloned the zebrafish moonshine gene and identified it as the ortholog of human TIF1gamma. Our analysis of zebrafish moonshine mutants demonstrates that TIF1gamma is essential for hematopoiesis. Mutations in zebrafish TIF1gamma disrupt embryonic and adult hematopoiesis resulting in severe red blood cell aplasia. TIF1gamma is one of three members of the TIF1 family of transcriptional intermediary factors. TIF1s are large nuclear proteins composed of a RING finger, two B-boxes, a Coiled coil domain, a PHD finger and Bromodomain. TIF1alpha has been identified as a cofactor for several nuclear hormone receptors and TIF1beta is a co-repressor for the large class of KRAB-ZFP transcription factors. In contrast, little is known about the function of TIF1gamma and there are no known transcription factor partners. In order to elucidate the molecular mechanisms of TIF1gamma function, this project has the following specific aims: 1) Functional analysis and comparison of TIF1alpha and TIF1gamma in hematopoiesis. This aim tests the hypothesis that TIF1alpka and TIF1gamma cooperate to regulate embryonic hematopoiesis. 2) Determination of the effect of SUMO-1 modification on TIF1gamma function in hematopoiesis. This aim tests the hypothesis that SUMO-1 modification of TIF1gamma is essential for embryonic hematopoiesis. 3) Identification of proteins that interact with TIF1gamma by yeast two-hybrid screens and functional analysis of these factors. This aim tests the hypothesis that there are transcription factors that form complexes with TIF1gamma and are also essential for hematopoiesis. This work will contribute to our understanding of hematopoietic gene regulation in normal development and should identify significant targets for clinical investigation of leukemias and congenital and acquired anemias in human patients.
Liao, E. C., Trede, N. S., Ransom, D., Zapata, A., Kieran, M. and Zon, L. I. (2002). Non-cell autonomous requirement for the bloodless gene in primitive hematopoiesis of zebrafish. Development 129, 649-59.
Parichy, D. M., Ransom, D. G., Paw, B., Zon, L. I. and Johnson, S. L. (2000). An orthologue of the kit-related gene fms is required for development of neural crest-derived xanthophores and a subpopulation of adult melanocytes in the zebrafish, Danio rerio. Development 127, 3031-44.
Ransom, D. G. and Zon, L. I. (1999). Mapping zebrafish mutations by AFLP. Methods Cell Biol 60, 195-211.
Thompson, M. A., Ransom, D. G., Pratt, S. J., MacLennan, H., Kieran, M. W., Detrich, H. W., 3rd, Vail, B., Huber, T. L., Paw, B., Brownlie, A. J. et al. (1998). The cloche and spadetail genes differentially affect hematopoiesis and vasculogenesis. Dev Biol 197, 248-69.
Ransom, D. G., Haffter, P., Odenthal, J., Brownlie, A. J., Vogelsang, E., Kelsh, R. N., Brand, M., van Eeden, F. J. M., Furutani-Seiki, M., Granato, M. et al. (1996). Characterization of zebrafish mutants with defects in embryonic hematopoiesis. Development 123, 311-319.
Zebrafish moonshine homozygous mutant embryos display severe defects in blood and mesenchymal cells. Two day old wild-type embryos have large numbers of red blood cells in circulation that stain brown with o-dianisidine (A, arrow). Moonshine mutant embryos are completely bloodless and show no staining (B, arrow). At 24 hours, wild-type embryos have few apoptotic cells that stain brightly with acridine orange (C). In contrast, homozygous mon mutants show extensive apoptosis of mesenchymal cells in the trunk and tail (D).
