CREB is critical for normal myelopoiesis in vitro. (A) (i) Western blot analysis demonstrating knockdown of CREB approaching 80% compared with control cells. (ii) Total numbers of CFU-GM colonies after 21 days in methylcellulose for murine hematopoietic cells. (iii) Flow cytometric analysis of murine bone marrow transduced with CREB shRNA or control lentivirus and sorted for GFP⁺ fraction, cultured in methylcellulose over 21 days. CREB knockdown cells had a lower fraction of mature granulocyte and monocytes compared with control cells. (B) (i) Western blot analysis demonstrating knockdown of CREB up to 65% compared with control cells. (ii) Total number of CFU-GM colonies after 21 days in methylcellulose for human peripheral blood stem cells. (iii) Flow cytometry analysis of transduced CD34⁺ human peripheral blood stem cells cultured in methylcellulose over 21 days. All experiments were performed in triplicate. Error bars in Aii,Bii represent SE.