Cell-cycle Dependent Differentiation of Friend Erythroleukemia Cells

Although Friend erythroleukemia (FL) cells have been largely believed to keep on proliferating after commitment for several generations before reaching the differentiated phenotype, there has been no certainity concerning the number of full cell cycles (CCs) necessary for these cells to be committed and differentiated in the presence of an inducer such as dimethylsulfoxide (DMSO). The present flow-cytometric analysis showed that FL cells,when treated simultaneously with thymidine and with DMSO, entered the culture growth cycle (CGC) with an S-phase, by conserving their potential to express hemoglobin (Hb). As a result of the double treatment,Hb was detected during the G1-phase of the third CC, while its maximal intracellular concentration was reached during G1 of the fourth CC (in the third CC DNA replication was significantly delayed by DMSO). Thus, one S was not sufficient for specific differentiation. The Hb increase occurred only when the inducer was present in the medium for a span of time including two subsequent Sphases. This, together with the measurement of the average length of the control FL cells lasting approximately 10 hrs, 240 min for G1, 180 min for S, 140 min for G2 and 40 min for M, showed that this basic finding was particularly supported by experiments which, at given points of the CGC, employed Colcemid to block mitosis or Aphidicolin (Aph) to block S.