GATA-1s rescues proplatelet formation, but not the hyperproliferative phenotype. (A) Constructs used in this study. Wild-type or mutant GATA-1 cDNAs were introduced into the MIGR1 vector backbone, which includes an IRES-GFP cassette. (B) GATA-1 expression in the rescued population was determined by qRT-PCR. There was no statistically significant difference between full-length GATA-1 and GATA-1s expression in the reconstitutions, but there was a significant difference between GATA-1 and V205G expression (P < .02). Means ± SD for 3 experiments are shown. (C) Light microscopy for the generation of proplatelet forms by the rescued cells. Notable features include the presence of proplatelets in the GATA-1s rescued cells and the presence of very large megakaryocytes in the population expressing V205G. Original magnification × 320. Images were obtained as described in the legend of Figure 1E. (D) AChE-stained cytospins of an aliquot of the 3-day cultures. Note the presence of a very large AChE-stained megakaryocyte in the population expressing V205G. Original magnification × 200. Images were obtained as described in the legend of Figure 1C. (E) Cell surface expression of CD41 on megakaryocytes after 3 days of in vitro differentiation, assayed by flow cytometry.