Discrimination of Dormant and Active Hematopoietic Stem Cells by G 0 Markers Reveals Dormancy Regulation by Basal Cytoplasmic Calcium

Quiescent hematopoietic stem cells (HSCs) are typically dormant, and only a few quiescent HSCs are active. The relationship between “dormant” and “active” HSCs remains unresolved. Here we generated a G0 marker mouse line that visualizes quiescent cells. The G0 marker identifies a population of active HSCs (G0 markerlow) which are rare and distinct from dormant HSCs (G0 markerhigh) within the conventional quiescent HSC fraction. Single-cell RNA-sequencing analyses showed that the gene expression profiles of these populations were nearly identical, yet differed in their Cdk4/6 activity. Furthermore high-throughput small molecule screening revealed that high levels of basal cytoplasmic calcium (Ca2+) protected the dormancy of HSCs from cell cycle activation induced by calcium influx. These findings indicate that the G0 marker separates dormant and active adult HSCs, which are regulated by Cdk4/6 and Ca2+ levels. This G0 marker mouse line represents a useful new resource for investigating physiologically important stem cell subpopulations.