IEX-1 expression in UT7-Mpl cells. (A) Northern blot analysis. UT7-Mpl cells were stimulated or not with 10 nM of peptide TPO. mRNA (10 μg/lane) was then isolated at the indicated times and analyzed by Northern blot using human IEX-1 as a probe. After stripping, the blot was rehybridized with GAPDH as an mRNA loading control. (B) CD34⁺ cells were isolated from human cord blood and were grown with 10 nM TPO during 12 days to generate megakaryocytes. The cells were either harvested directly (lane 1) or after starvation for 3 hours in medium without TPO (lane 2) and restimulation with 10 nM of TPO for 3 hours (lane 3). Immunoblotting with anti-IEX1 antibody was performed. Antiactin antibody was used as a loading control.