Differential Sensitivity of Mouse Hematopoietic Stem Cells to Merocyanine 540

In vivo and in vitro clonal assays of immature mouse blood cells showed that diffferent populations of hematopoietic progenitor cells differ considerably with respect to their sensitivity to photodynamic damages caused by the fluorescent dye Merocyanine 540. Late erythroid progenitors were the most sensitive cells followed in order of decreasing sensitivity by pluripotent stem cells, early erythroid progenitors, and granulocyte/macrophage progenitors. Only about 2%–4% of all nucleated marrow cells were stained with Merocyanine 540 which correlated well with current frequency estimates of progenitor cells in mouse bone marrow. Our findings indicate that the expression of Merocyanine binding sites is developmentally regulated and might, therefore, provide a useful molecular marker for blood cell differentiation and a basis for an effective purification of hematopoietic progenitor cells.