Reduced number of cells per CFU-Mk in the absence of NF-E2 function. (A) Quantification of mean number of cells per CFU-Mk based on counting cells from 100 colonies derived from control (+/+ or +/−, designated as +/?, N = 10) and mutant (−/−, N = 5) fetal livers. Statistical significance was established using the Student’s t-test, P = .003. (B) Bright-field photomicrographs of representative individual megakaryocyte colonies at day 7 from control (left) and mutant (right) fetal livers (original magnification × 200). (C) RT-PCR analysis for c-Mpl (left) and control (hypoxanthine phosphoribosyl transferase, HPRT, right) mRNA levels in wild-type (+/+) and NF-E2–deficient (−/−) megakaryocytes. Numbers refer to PCR cycles.