Analysis of megakaryocytes and megakaryocytic gene expression in the Fli-1^–/– and GABPαtp/tp mice. (A) Total fetal liver cells from E11 at 12 hours culture as in Figure 2 were used to study the relative number of immature and mature megakaryocytes in fetal hematopoietic tissue. These cells were stained with FITC-conjugated anti-CD41 and phycoerythrin (PE)–conjugated anti-GPIbα antibodies and subjected to flow cytometry. Top left shows the analysis of 9 Fli-1^–/– fetal liver samples and 9 WT littermates. Bottom left shows the analysis of 6 GABPαtp/tp fetal liver samples and 6 WT littermates. At the right of the figure, the relative levels of mature to immature megakaryocytes for each phenotype compared to their WT siblings are shown. * = P < .005; ** = P < .001; and *** = P < .0001 relative to WT control. The mean ± one SD is shown for each study. (B) Megakaryocyte-specific gene expression patterns in Fli-1^–/– and GABPαtp/tp mice fetuses were studied using RNA extracted from E11 embryos (left 2 panels) or E12.5 fetal liver cells (right panel) and subjected to real-time RT-PCR for the messages indicated. The number of fetuses studied in each group is indicated. For all studies, * = P < .005; ** = P < .001; *** = P < .0001; and **** = P < .000 01 relative to WT control. The mean ± one SD is shown for each study.