Establishment of normal, terminally differentiating mouse erythroid progenitors:: molecular characterization by cDNA arrays

Expression profiling with cDNA arrays is an excellent tool for molecular analysis of complex processes such as terminal erythroid differentiation. The shortcomings of the currently available erythroid in vitro differentiation models, however, severely impaired the usefulness of this approach to study erythropoiesis. Here, we describe a novel, murine erythroid cell system closely corresponding to in vivo erythroid progenitors. Mortal, long-term proliferating erythroid progenitors of fetal liver or immortal strains of p53-deficient erythroblasts were established in culture. Both cell types proliferated in serum-free medium and were strictly dependent on physiologically relevant cytokines and hormones, stably retaining a diploid set of chromosomes. If exposed to physiological differentiation factors (erythropoietin plus insulin), cells synchronously recapitulated the normal in vivo differentiation program to mature terminally into enucleated erythrocytes and expressed stage-specific erythroid transcription factors in the expected temporal order. Using cDNA arrays, we found a large number of genes differentially expressed at time points during differentiation. Already 6 h after differentiation induction, 17% of the expressed genes showed significant alterations in mRNA abundance, increasing to 53% (12% up-regulated, 41% down-regulated genes) by 48 h. Cluster analysis of mRNA expression kinetics during differentiation identified six distinct expression patterns. All genes on the array with a known function in erythropoiesis showed the expected variations in expression. The genes identified also allowed first insights into the sequence of events within the regulatory network responsible for erythroid maturation. In mortal wild-type as well as immortal p53(-/-) erythroblasts, changes in mRNA abundance of several well-regulated gene products was verified at the protein level. Taken together, this novel hematopoietic cell system faithfully executes essential steps of normal erythropoiesis and allows us to dissect and characterize molecular mechanisms involved in erythropoiesis.