Grant: CIHR Fellowship

Hematopoietic stem cells supply all the blood cells required during life. During development stem cells migrate to vascular niches where they are enveloped by 'cuddling' endothelial cells and contacted by stromal cells. These stromal cells sustain the stem cells by releasing signals that encourage stem cell self-renewal. Contact with stromal cells also controls how the stem cells divide, ensuring that one of the dividing cells remains in the niche, while the other leaves to form mature blood cells. This makes stromal cells essential to the niche and if they are destroyed the stem cells can be lost leading to blood disorders. Despite the importance of these niche stromal cells no study has yet identified what makes them unique and what specific mechanisms they use to regulate stem cell division. This research will characterize stromal cells using zebrafish models which have many of the same cell types and signaling pathways as the mammalian bone marrow niche. Next generation sequencing technologies will be used to examine stromal cells at single cell resolution and identify the cell types that form the niche. Using this data, the genetic factors that specify niche stromal cells will be determined and used to build tools to target the niche. Stem cell divisions will be visualized within the optically clear zebrafish embryos using 4D microscopic imaging. Polarized proteins previously identified in isolated mammalian stem cells extracted from bone marrow will be fluorescently tagged and expressed in the zebrafish stem cells to visualize cell polarity and asymmetric divisions in context within the niche. Genetic ablation of stromal cells will then test the requirements for these cells in blood homeostasis. The results of this research will deepen our understanding of the stem niche and inform therapeutic strategies to improve the expansion of transplanted stem cells for the treatment of blood disorders.