Fig. 4. Defective erythropoiesis in the absence of endoglin. (A) Eng^+/+, Eng^+/- and Eng^-/- ES cells were assayed for primitive erythroid development by plating cells from EBs differentiated for 3, 4 and 5 days (d3, d4 and d5, respectively) in methylcellulose (MCM) supplemented with IL-3, IL-6, SCF and EPO. (B) Relative levels of SCL, GATA2, RUNX1, GATA1, embryonic and adult globins, GPIIB (CD41), NFE2, and FMS from Eng^+/+ and Eng^-/- day 3, 4 and 7 EBs by real-time RT-PCR. Transcripts are normalized to GAPDH. (A,B) Error bars indicate standard deviations from three independent experiments performed in duplicate. ^*, P<0.05; ^**, P<0.005; ^***, P<0.0001; versus controls (+/+ and -/-). (C) FACS analyses of day 6 Eng^+/+ and Eng^-/- EBs for GPIIB (CD41) and c-KIT. Fluorescence intensity for c-KIT is indicated on the y axis and for GPIIB (CD41) on the x axis.