Figure 1.

Models of hierarchical differentiation of HSC. (a) Classical “step-wise” model of hematopoiesis. HSCs differentiate into terminally differentiated cell types through discrete hierarchically organized progenitor populations. In this model, HSCs are thought to be homogeneous and multipotent to be differentiated to any cell types. (b) “Continuous” differentiation model of hematopoiesis. Recent advances in single-cell RNA sequencing revealed that HSCs are a more heterogeneous population consisting of cells with lineage-specific fates and HSCs differentiate into specific cell types without any major transition through the multi- and bipotent progenitors as described in “step-wise” model. HSC, hematopoietic stem cell.