Imaging methods used to study mouse and human HSC niches: Current and emerging technologies.

Bone marrow contains numerous different cell types arising from hematopoietic stem cells (HSCs) and non-hematopoietic mesenchymal/skeletal stem cells, in addition to other cell types such as endothelial cells- these non-hematopoietic cells are commonly referred to as stromal cells or microenvironment cells. HSC function is intimately linked to complex signals integrated by their niches, formed by combinations of hematopoietic and stromal cells. Studies of hematopoietic cells have been significantly advanced by flow cytometry methods, enabling the quantitation of each cell type in normal and perturbed situations, in addition to the isolation of these cells for molecular and functional studies. Less is known, however, about the specific niches for distinct developing hematopoietic lineages, or the changes occurring in the niche size and function in these distinct anatomical sites in the bone marrow under stress situations and ageing. Significant advances in imaging technology during the last decade have permitted studies of HSC niches in mice. Additional imaging technologies are emerging that will facilitate the study of human HSC niches in trephine BM biopsies. Here we provide an overview of imaging technologies used to study HSC niches, in addition to highlighting emerging technology that will help us to more precisely identify and characterize HSC niches in normal and diseased states.