Dynamic regulation of Fbw7 expression during HSC cycle entry and differentiation. (A) Flow-purified LSK cells were cultured with cytokines for 0, 1, or 2 d and were stained for intracellular Ki-67 and DNA content (DAPI). (B) Fbw7 and Cul1 mRNA expression were analyzed by quantitative RT-PCR on each day. (C) Quantification of Sca-1 expression (loss of Sca-1 indicates differentiation of LSK cells) after each day of culture. On day 0, all cells are Sca-1⁺.