In vivo divisional tracking of hematopoietic stem cells.

Hematopoietic stem cell (HSC) division leads to self-renewal, differentiation, or death of HSCs, and adequate balance of this process results in sustained, lifelong, high-throughput hematopoiesis. Despite their contribution to hematopoietic cell production, the majority of cells within the HSC population are quiescent at any given time. Recent studies have tackled the questions of how often HSCs divide, how divisional history relates to repopulating potential, and how many HSCs contribute to hematopoiesis. Here, we summarize these recent findings on HSC turnover from different experimental systems and discuss hypothetical models for HSC cycling and maintenance in steady-state and upon hematopoietic challenge.