Fig. 4.

HSCs are dormant and solitary in the bone marrow niche. (A and B) Frozen bone sections from EIS-KI mice were stained with PE-conjugated anti-Sca1 antibody. The green fluorescent images (Left) were merged with Nomarski and PE images (Right). A and B are photographs from independent mice. GFP or Sca1 single-positive cells are indicated with green (long arrows) or red, respectively. Yellow cells (short arrows) indicate GFP/Sca1 double-positive cells that reside by the edge of the bone marrow. The bone marrow sections were also stained with anti-GFP antibody (arrows, brown) and alkaline phosphatase (purple in C) or Alcian blue (D). GFP⁺ cells are in direct contact with purple-stained osteoblasts (C), but not with the Alcian blue⁺ cartilage (D). (E) Green fluorescent (Left) and bright field (Right) images of living bone marrow from the scapula of an EIS-KI mouse 1 day after 5-FU injection. GFP⁺ cells are detected near the edge of the bone marrow. (F and G). Two days after 5-FU administration, GFP⁺ cells are apparently quiescent, deep in the bone marrow. Time-lapse images of E, F, and G are exhibited in Movies 1–3. The movies demonstrate that GFP⁺ cells are almost completely immobilized in the bone marrow, whereas the surrounding GFP⁻ cells move vigorously.