Expression data from murine fetal liver cells, combinations of RB1 family knockouts

Retinoblastoma-1 (RB1), and the RB1-related proteins p107 and p130, reside at a central node in the cell cycle regulatory network. RB1 is required for normal erythroid development in vitro, but is largely dispensable for erythropoiesis in vivo. The modest phenotype caused by RB1 deficiency in mice raises questions about redundancy within the RB1 family, and the role of RB1 in erythroid differentiation. Here we show that RB1 is the major pocket protein that regulates terminal erythroid differentiation. Erythroid cells lacking all pocket proteins exhibit the same cell cycle defects as those deficient for RB1 alone. Further, we show that RB1 broadly represses gene expression in erythroid cells, coincident with the transition from precursor to terminally differentiated cell. RB1-repressed genes are well expressed but downregulated at the final stage of erythroid development. By merging differential and time-dependent changes in expression, we define a group of approximately 800 RB1-repressed genes. As anticipated, these genes are enriched for terms such as cell cycle and DNA metabolic process, but also for terms such as mRNA processing, chromosome organization, and ubiquitin-mediated protein catabolic pro-cess. Our results suggest that RB1-mediated repression of genes involved in noncanonical processes has a central role in terminal erythroid differentiation.

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