Guest editorial: Regulatory signaling in normal and abnormal hematopoiesis.

Stem cells are characterized by their unique ability to both self-renew and differentiate along multiple cellular lineages. Self-renewal and differentiation must be tightly controlled to ensure an appropriate stem cell pool in tissue over the lifetime of an organism. Elucidating the mechanisms controlling stem cell fate and maintenance remains a key challenge in stem cell biology. Hematopoietic stem cells (HSCs) are responsible for the lifelong production of multiple blood cell lineages. To remain functional, these cells must interact with a particular microenvironment, known as the stem cell niche. HSC niches provide various factors, including cytokines, extracellular matrices, nutrients, hormones, and metabolites. These niche factors modulate cell-intrinsic molecular regulatory networks in HSCs. Niche signals also play crucial roles in the induction of HSCs from pluripotent stem cells or vascular endothelial cells. The Progress in Hematology review series in the current issue highlights some critical regulators of HSC maintenance and production.