Expression of cell-survival genes, Bcl-2 and Bcl-XL, is not sufficient for the erythroid colony formation from CFU-E in fetal liver cells but enhances erythroid colony formation from CFU-E in response to EPO. (A) Expression of Bcl-2 or Bcl-XL in Ba/F3 cells prolongs cell survival. Ba/F3 cells were infected with retrovirus encoding Bcl-2 or Bcl-XL or the empty virus vector. GFP-positive cells were collected by FACS and cultured in the absence of cytokine, and their viability was monitored by the Trypan blue exclusion assay. (B) Fetal liver cells were infected with retrovirus encoding Bcl-2 or Bcl-XL or the empty virus vector. GFP-positive cells were collected by FACS. P shows the GFP-positive cell population subjected to the CFU-E assays. (C) Sorted GFP-positive cells were subjected to in vitro colony assays. The relative CFU-E colony numbers were calculated as the ratio of CFU-E colony numbers of fetal liver cells infected with retrovirus vector without any cDNA insert. The mean ± SEM for five independent experiments are shown.