Phase-contrast micrographs of control (a; +/+) and NF-E2-deficient (b; −/−) megakaryocytes on day 5 of culture of fetal liver cells in the c-Mpl ligand. The hematopoietic cells growing in suspension, and easily distinguished from the adherent stromal cells (straight arrow in [a], right panel), are mostly large and small megakaryocytes but include few myeloid and erythroid cells. Wild-type cultures (a) show abundant proplatelets characterized by platelet-size structures (curved arrows in [a]) on an extensive system of filamentous processes. Mutant cultures (b), here shown at higher cell density to include more cells in each microscopic field, never produce proplatelets. Original magnification × 200.