Cell
Volume 126, Issue 4, 25 August 2006, Pages 755-766
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Article
Multilineage Transcriptional Priming and Determination of Alternate Hematopoietic Cell Fates

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Summary

Hematopoietic stem cells and their progenitors exhibit multilineage patterns of gene expression. Molecular mechanisms underlying the generation and refinement of these patterns during cell fate determination remain unexplored because of the absence of suitable experimental systems. Using PU.1−/− progenitors, we demonstrate that at subthreshold levels, this Ets transcription factor regulates a mixed pattern (macrophage/neutrophil) of gene expression within individual myeloid progenitors. Increased PU.1 levels refine the pattern and promote macrophage differentiation by modulating a novel regulatory circuit comprised of counter antagonistic repressors, Egr-1,2/Nab-2 and Gfi-1. Egr-1 and Egr-2 function redundantly to activate macrophage genes and to repress the neutrophil program. These results are used to assemble and mathematically model a gene regulatory network that exhibits both graded and bistable behaviors and accounts for the onset and resolution of mixed lineage patterns during cell fate determination.

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These authors contributed equally to this work.

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Present address: Korea Research Institute of Bioscience and Biotechnology, Proteome Research Lab, #52 Oun-dong, Yusong-gu, Taejon 305-333, Korea.