Promyelocyte self-renewal requires continuous nuclear Hhex expression. (A) Growth curves showing expansion of promyelocytic cell lines expressing Hhex or Hhex^ERT2 fusion protein in the presence or absence of tamoxifen (Tam). (B) Viability of Hhex^ERT2 cell lines cultured as in panel A, as assessed by exclusion of Fluoro-Gold. (C) Induction of the myeloid differentiation marker Gr-1 on a Hhex^ERT2 line (as in panel A) upon culture without tamoxifen (-Tam). (D) Morphology of Hhex^ERT2-transformed promyelocytic cell line cultured in the presence or absence of tamoxifen for 7 days. Cells were stained with Wright-Giemsa (original magnification ×400). Data are representative of 2 separate experiments. Max, maximum.