Hematopoietic progenitors undergo differentiation while navigating several cell division cycles, but it is unknown whether these two processes are coupled. We addressed this question by studying erythropoiesis in mouse fetal liver in vivo. We found that the initial upregulation of cell surface CD71 identifies developmentally matched erythroblasts that are tightly synchronized in S-phase. We show that DNA replication within this but not subsequent cycles is required for a differentiation switch comprising rapid and simultaneous committal transitions whose precise timing was previously unknown. These include the onset of erythropoietin dependence, activation of the erythroid master transcriptional regulator GATA-1, and a switch to an active chromatin conformation at the β-globin locus. Specifically, S-phase progression is required for the formation of DNase I hypersensitive sites and for DNA demethylation at this locus. Mechanistically, we show that S-phase progression during this key committal step is dependent on downregulation of the cyclin-dependent kinase p57KIP2 and in turn causes the downregulation of PU.1, an antagonist of GATA-1 function. These findings therefore highlight a novel role for a cyclin-dependent kinase inhibitor in differentiation, distinct to their known function in cell cycle exit. Furthermore, we show that a novel, mutual inhibition between PU.1 expression and S-phase progression provides a "synchromesh" mechanism that "locks" the erythroid differentiation program to the cell cycle clock, ensuring precise coordination of critical differentiation events.

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Keywords CD71 antigen, DNA replication, animal cell, animal tissue, article, beta globin, cell cycle S phase, cell cycle clock, cell cycle progression, cell differentiation, cell division, cell synchronization, chromatin, controlled study, cyclin dependent kinase inhibitor 1C, demethylation, deoxyribonuclease I, embryo, erythroblast, erythroid cell, erythropoiesis, erythropoietin, fetus liver, hematopoietic stem cell, in vivo study, mouse, nonhuman, periodicity, transcription factor GATA 1, transcription factor PU 1, upregulation
Persistent URL dx.doi.org/10.1371/journal.pbio.1000484, hdl.handle.net/1765/21357
Journal P L o S Biology (Print)
Pop, R, Shearstone, J.R, Shen, Q, Liu, Y, Hallstrom, K, Koulnis, M, … Socolovsky, M. (2010). A key commitment step in erythropoiesis is synchronized with the cell cycle clock through mutual inhibition between PU.1 and S-phase progression. P L o S Biology (Print), 8(9), 1–19. doi:10.1371/journal.pbio.1000484