FIG. 2.

Conditional expression of C/EBPα is sufficient for induction of granulocytic differentiation of bipotential U937 cells. Two individual stable clones of U937 cells with an empty expression vector, U937(vect)#1 (A) and U937(vect)#3 (B), were grown in zinc-containing medium for 17 days. Three individual clones of U937 cells were transfected with an inducible C/EBPα expression vector and grown in the absence of zinc (C [U937α#2]) or the presence of zinc for 17 days (D [U937α#2], E [U937α#3], and F [U937α#5]). Cell aliquots were centrifuged onto glass slides and stained with Wright-Giemsa stain. N, representative cell with the appearance of a polymorphonuclear granulocyte.