Abstract
dc:description.abstract<p>Previous work has identified <italic>Mesp1</italic> as an important regulator of the epithelial–mesenchymal transition: EMT) and of cardiovascular cell fate in differentiating embryonic stem cells: ESCs). To understand the molecular mechanisms underlying the actions of <italic>Mesp1</italic>, we sought to identify transcription targets of <italic>Mesp1</italic>. <italic>Mesp1</italic> rapidly induced expression of PDGFRα in differentiating ESCs and directly bound to evolutionary conserved E-boxes within the PDGFRα promoter. This result suggested that PDGFRα could be a direct target of <italic>Mesp1</italic>. However, we found that PDGFRα was not sufficient for the induction of EMT in ESCs or the induction of Flk1<super>+</super> mesoderm, but that it may play a role rather in the survival of <italic>Mesp1</italic>–induced mesodermal cells.</p><p>Although a clear role for <italic>Mesp1</italic> in EMT and cardiovascular differentiation has been established, its function in hematopoietic development is still unclear. Previous lineage tracing demonstrated that <italic>Mesp1</italic> activity labeled endothelial cells of embryonic dorsal aorta, which recently was shown to give rise to definitive hematopoietic progenitors. This suggested the potential that <italic>Mesp1</italic> activity in endothelium might influence subsequent hematopoietic development. Although <italic>in vitro</italic> studies indicated that <italic>Mesp1</italic> acted to suppress emergence of hematopoietic progenitors, we made the surprising observation in lineage tracing analysis of <italic>Mesp1</italic> that all adult hematopoietic progenitors and mature lineages were efficiently labeled by <italic>Mesp1</italic>–Cre, and further that <italic>Mesp1</italic> was necessary for hematopoietic differentiation of ESCs. In examining the downstream targets of <italic>Mesp1</italic> in ESC–derived endothelial cells, we identified myeloid ecotropic viral integration site 1: <italic>Meis1</italic>).</p><p>Meis1 forms a heterodimer with Pbx1 that augments Hox-dependent gene expression. In addition, <italic>Meis1</italic> has been associated with leukemogenesis and hematopoietic stem cell self-renewal. In examining potential roles of <italic>Meis1</italic> in hematopoietic development, we identified two independent actions. One activity regulated cellular proliferation of early hematopoietic progenitors. The second activity was involved the fate choice between erythroid and megakaryocyte lineages. First, we found that endogenous <italic>Mesp1</italic> indirectly induces <italic>Meis1</italic> and <italic>Meis2</italic> in endothelial cells derived from embryonic stem: ES) cells. Overexpression of <italic>Meis1</italic> and <italic>Meis2</italic> greatly enhanced the formation of hematopoietic colonies from ES cells, with the exception of erythroid colonies, by maintaining hematopoietic progenitor cells in a state of proliferation. Second, overexpression of <italic>Meis1</italic> repressed the development of early erythroid progenitors, acting <italic>in vivo</italic> at the megakaryocyte–erythroid progenitor: MEP) stage to skew development away from erythroid generation and toward megakaryocyte development. This previously unrecognized action of <italic>Meis1</italic> may explain the embryonic lethality observed in <italic>Meis1</italic><super>-/-</super> mice that arises from failure of lymphatic–venous separation, and which can result as a consequence of defective platelet generation. These results show that <italic>Meis1</italic> exerts two independent functions, with its role in proliferation of hematopoietic progenitors acting earlier in development from its influence on the fate choice at the MEP between megakaryocytic and erythroid development.</p>
Degree
thesis:*- Name thesis:degree_name
- Doctor of Philosophy (PhD)
- Level thesis:degree_level
- Dissertation
- Discipline thesis:degree_discipline
- Biology and Biomedical Sciences: Molecular Cell Biology
- Year dc:date.available
- 2012
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Cai, Mi
- Contributors dc:contributor
-
- Kenneth M Murphy
Subjects
dc:subject × 6Rights
- Language dc:language
- English (en)
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:openscholarship.wustl.edu:etd-1944