Genetic dissection of mesodermal commitment to the hematopoietic fates.

Genetic dissection of mesodermal commitment to the hematopoietic fates.

Funding Type: 
New Faculty I
Grant Number: 
RN1-00575
Award Value: 
$2,150,620
Status: 
Closed
Public Abstract: 
Statement of Benefit to California: 
Progress Report: 

Year 1

I am pleased to report that we have continued to make considerable progress on my CIRM New Investigator Award. In the past year, we have helped solve a long-standing controversy in the field of developmental hematopoiesis as to exactly where the first hematopoietic stem cells (HSCs) are born in the embryo. Using the strategies outlined in Aim 2 of this proposal, we demonstrated that HSCs are born from hemogenic endothelial cells lining the ventral floor of the dorsal aorta (Bertrand and Chi et al., Nature 464: 108-111). This new knowledge will be immensely helpful in continuing our genetic dissection of how HSCs are patterned from mesoderm, as we now know precisely when and where HSCs arise, and that a requisite step in their formation is through an endothelial intermediate. In addition, we have made excellent progress on Aims 3 and 4. Under Aim 3, we have recently demonstrated that, of the four independent waves of hematopoietic precursors that arise in the vertebrate embryo, Notch signaling plays a role only in HSC formation (Bertrand and Cisson, Blood, ePub 1/27/10). Furthermore the requirement for Notch signaling in HSCs is absolute, in that no HSCs are formed in the absence of all Notch ligands. These findings are guiding our studies in Year 3. Finally, under Aim 4, we have completed our first set of experiments on the role of Wnt16 in HSC formation and will submit a manuscript to Nature within the month. Wnt16 morphants lack HSCs, and transient induction of Notch signaling in Wnt 16 morphants rescues HSC development. We have demonstrated that Wnt16 lies genetically upstream of DllC and DllD, and shown, of the seven Notch ligands, that these two are necessary for HSC specification. These findings are important, since very little is known regarding the roles of Wnt signaling in HSC formation.

Year 2

Over the past year, we have made excellent progress on my CIRM New Investigator Award. We have demonstrated using direct imaging approaches that hematopoietic stem cells (HSCs) are born from hemogenic endothelial cells lining the ventral floor of the dorsal aorta (Bertrand and Chi et al., Nature 464: 108-111). This finding has allowed us to refine our approaches, knowing now that HSC specification requires transition through an aortic endothelial intermediate. Moving forward, our major goals are to understand how Wnt and Notch signaling integrate to regulate the specification of hemogenic endothelium. Our efforts over the past year have demonstrated that Wnt16 acts as a novel regulator of HSC fate through its regulation of two Notch ligands. Intriguingly, this pathway is non-cell autonomous with respect to HSCs and thus represents one of the earliest known extrinsic regulators of HSC fate specification. Our discovery of this pathway may therefore be a critical link that has been missing in the efforts to instruct HSCs in vitro from pluripotent precursors.

Year 3

Hematopoietic stem cells are an important population of cells that continuously produce and replace all blood and immune system cells throughout life. These rare cells are responsible for the curative effects of bone marrow transplants, which are used to treat a variety of conditions including many forms of blood cancer. Understanding how hematopoietic stem cells are made during embryonic development is important because it could teach us how to make such cells in the laboratory, and possibly allow circumvention of donor immune compatibility issues. In this research we describe a previously unknown set of molecular inputs that are required to make hematopoietic stem cells during embryonic development. Of note, this signaling pathway is required for environmental instruction of hematopoietic stem cells, meaning we are one step closer to understanding how to generate them in vitro. Eventually these findings may help us discover the complete set of molecular controls necessary for making hematopoietic stem cells.

Year 4

Hematopoietic stem cells are an important population of cells that continuously produce and replace all blood and immune system cells throughout life. These rare cells are responsible for the curative effects of bone marrow transplants, which are used to treat a variety of conditions including many forms of blood cancer. Understanding how hematopoietic stem cells are made during embryonic development is important because it could teach us how to make such cells in the laboratory, and possibly allow circumvention of donor immune compatibility issues. In this research we describe a previously unknown set of molecular inputs that are required to make hematopoietic stem cells during embryonic development. Of note, this signaling pathway is required for environmental instruction of hematopoietic stem cells, meaning we are one step closer to understanding how to generate them in vitro. Eventually these findings may help us discover the complete set of molecular controls necessary for making hematopoietic stem cells.

© 2013 California Institute for Regenerative Medicine