Abstract

Extract: Stem cells modulate tissue formation and repair based on a complex interaction of cell autonomous and non-autonomous regulatory mechanisms. While reductionist approaches to understanding stem cell control continue to be extremely productive, understanding the physiological contexts in which stem cells function, will ultimately require definition of the microenvironments in which they live. The location of stem or precursor populations within numerous solid tissues has been described, but delineating specific associated cells and how they participate in regulating stem cell function has generally been lacking for mammalian tissues. However, the use of invertebrate-based models has created particularly productive systems in which to examine the niche context of stem cells. Gonadal tissue from C. elegans and D. melanogaster has permitted the definition and identification of ancillary niche cells, physical interactions and the molecular pathways such as Notch paralogues that govern the interplay between the stem cell and its local environment. We sought to determine a niche component for a mammalian tissue and focused on the hematopoietic system. We focused on hematopoiesis for multiple reasons, but in particular because of the potential for applying the information gained to a medical context.