Rescue of the Gata1 knockout by βLCR-driven Gata transgenes. (A) Characterization of βLCR-G transgenic mice. Western blot analysis of E12.5 fetal liver cells from βLCR-G1, βLCR-G2, and βLCR-G3 transgenic lines showing different expression levels of the transgene-derived Gata factors. Gata1 expression of the G1OX line¹⁰  is shown for comparison with the βLCR-G1 lines; X:X = heterozygous female; X:Y = hemizygous male. Staining of the same blots with an antibody against nucleophosmin (Npm1) was used as a loading control. (B) Rescue of the Gata1 knockout by the βLCR-G transgenes. Fetuses were isolated at the time points indicated; the bars represent the number of βLCR-G::G1KO:Y fetuses divided by the number expected according to Mendelian inheritance. n = total number of fetuses isolated. NB = newborn. Green: alive fetuses of normal size; blue: growth retarded fetuses; black: dead fetuses. **: number observed lower than expected; P < 0.01. (C) Rescue of G1KO fetuses by the βLCR-G1 transgene (line B) at E12.5. Top panel: E12.5 fetuses of genotypes indicated. Middle panel: their fetal livers. Bottom panel: erythroid cells from the circulation. (D) The βLCR-G1 transgene (line B) can rescue G1KO fetuses until E15.5. Top panel: E15.5 fetuses of genotypes indicated. Bottom panel: erythroid cells from the circulation; the percentage of nucleated cells is indicated; original magnification, 40×.