Myc up-regulation is required for BCR-triggered proliferation and differentiation arrest of B cells. (A-F) These experiments were performed on magnetically separated total untouched B cells from spleen of transgenic mice and their wild-type controls. Cells were analyzed either freshly isolated or after in vitro incubation with (BCR) or without (ctrl) anti-μ F(ab')2 for the indicated periods of time. (A) Measurements of ATP content in cells that were treated with anti-μ F(ab')2. Results are mean ± s.d. of two independent experiments performed in triplicate. (B) Cells were incubated with anti-μ F(ab')2 unperturbed for 48 h, photographed under phase-contrast microscope (top) and then stained with propidium iodide (PI) for cell cycle analysis (bottom). Live cell gating is shown. Data are representative of two or three experiments. (C) Transcriptional regulation of cell cycling genes in mature Myc+/+ and MycΔ/Δ B cells was examined by qPCR at 18 h of BCR-triggering. (D) Measurements of caspase 3/7 activity of cells treated with anti-μ F(ab')2. (E) ELISA of IgM in supernatants of unstimulated Mycfl/Δ and MycΔ/Δ B cells. Data are mean ± s.e.m. of three independent experiments. (F) Steady-state mRNA levels of terminal differentiation-associated genes in resting mature Myc+/+ and MycΔ/Δ B cells.