Proliferation profiles of normal (WT) and neo▵HS (MUT) primary megakaryocytes expanded from fetal liver cells in liquid culture in recombinant Tpo. The number of cells with acetylcholinesterase (AchE) activity in 50-μL aliquots of the culture is shown as a function of the duration of culture. The values shown are the mean ± 1 SD from separate cultures of 15 normal and 15 mutant fetal livers.