Expression of Notch-1 and Notch-2 by mouse BM cells. (A) Fluorescence histograms of Ficoll-Hypaque–separated marrow cells stained with MoAbs that recognize Notch-1 (18G) or Notch-2 (BHN6). (B) Fluorescence histograms of precursor cells (Lin⁻Sca-1⁺c-kit⁺) stained with the same MoAbs as in (A). The x-axis represents log fluorescence intensity and the y-axis represents cell number. The solid line represents staining with 18G or BHN6 antibodies and the dashed line represents staining with an isotype-matched nonspecific antibody.