Scl haplodeficiency decreases mean stem cell activity. (A) Experimental scheme. Bone marrow cells from adult Scl^+/− mice and Scl^+/+ littermates or age-matched controls were processed in parallel. (B) Western blot of total protein extracts were used to assess SCL and E2A protein levels in Scl^+/+ and Scl^+/− lineage-depleted bone marrow cells. Anti-PTP1D was used as a loading control. Ratio of chemiluminescent intensities from Scl^+/− over Scl^+/+ samples are shown on the right. (C) The frequency of LT-HSCs in Scl^+/+ and Scl^+/− mice was assessed by flow cytometric analysis of Kit⁺Sca1⁺Lin⁻CD150⁺CD48⁻ cells. Shown are box plots with the median and extreme values of each distribution (n mice per group). The 2 distributions are not significantly different (P = .1). (D) The mean stem cell activity (MAS) was calculated in mice receiving approximately 1 CRU, as described in “Transplantation assays.” Box plots as above from n mice; P values as shown.