Proliferation and apoptosis in Mx1-Cre, Nf1 ^flox/flox and Cre^- mice. (A) BrdU incorporation in vivo by Cre⁺ and Cre^- bone marrow cells and splenocytes. Increased proliferation is seen in the spleens of Cre⁺ mice (14.6% versus 4.5% labeled cells). (B) BrdU labeling of Mac1⁺ cells from Cre⁺ and Cre^- mice. A higher percentage of splenic Mac1⁺ cells were labeled (20% versus 6.6%). (C) Annexin V staining of bone marrow mononuclear cells from Cre^- and Cre⁺ mice showing greatly reduced apoptosis of Cre⁺ cells after 24 hours in culture without exogenous growth factors (27.9% versus 74.5% in the controls). The histograms present representative data from an analysis of 3 mice of each genotype. The numbers shown in each panel indicate the percentage of positive cells.