Functional Characterization of Homeodomain Transcription Factors and Retinoic Acid Signaling in Hematopoiesis

  • Author / Creator
    Laura Pillay
  • Improper regulation of hematopoiesis generates a spectrum of defects that range from anemia and embryonic lethality to leukemia. Identifying the molecular pathways that regulate hematopoiesis is therefore a major goal of both basic and clinical biology. Vertebrate hematopoiesis occurs in two embryonic waves. The first wave, primitive hematopoiesis, influences the morphology of the developing embryonic circulatory system and produces circulating erythrocytes that facilitate tissue oxygenation during periods of rapid embryonic growth. The second, definitive wave of hematopoiesis produces multipotent hematopoietic stem cells (HSCs) that are able to differentiate into all mature blood cell lineages, self-renew, and maintain adult hematopoiesis for life. A major challenge in developmental hematopoiesis is to determine the molecular cues that regulate each phase of hematopoiesis. Previous analyses using vertebrate models have identified molecular pathways that govern both primitive and definitive hematopoiesis. These pathways are conserved among vertebrates, and the critical mammalian hematopoietic genes have clear orthologues in zebrafish. Using zebrafish as a model organism, we have identified essential regulators of both primitive and definitive hematopoiesis. We have defined a critical role for the homeodomain transcription factors Meis1 and Pbx in regulating primitive erythropoiesis. Inhibiting zebrafish Meis1 and Pbx protein synthesis cripples the production of circulating erythrocytes, and generates defects in erythropoietic gene expression. Our data place Meis1 and Pbx upstream of gata1 in the erythropoietic transcription factor hierarchy. We have also elucidated a novel role for retinoic acid (RA) signaling in definitive hematopoiesis, as RA-depleted embryos fail to produce HSCs. Previous studies have implicated RA as a critical regulator of murine Notch1 signaling, and suggest that endothelial cells require RA in order to adopt a hemogenic fate. However, our research suggests that RA is required for HSC formation prior to the formation of dorsal aorta hemogenic endothelium and that, unlike in mice, zebrafish RA does not regulate HSC formation through the Notch1-signaling pathway. Previous research by our lab has implicated the homeodomain transcription factor Hmx4 as a critical regulator of zebrafish forebrain and ocular development, and has shown that Hmx4 modulates RA signaling. However, prior to this work, the contribution of Hmx4 to embryonic hematopoiesis was unknown. We have identified putative RA-independent and dependent roles for Hmx4 in regulating primitive and definitive hematopoiesis, respectively.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Biological Sciences
  • Specialization
    • Molecular Biology and Genetics
  • Supervisor / co-supervisor and their department(s)
    • Waskiewicz, Andrew J. (Biological Sciences)
  • Examining committee members and their departments
    • Pharmacology, University of Massachusetts Medical School)
    • Waskiewicz, Andrew J. (Biological Sciences)
    • Ali, Declan W. (Biological Sciences)
    • Sagerstrom, Charles G. (Biochemistry and Molecular)
    • Pilgrim, David B. (Biological Sciences)
    • McDermid, Heather E. (Biological Sciences)