The order of expression of transcription factors directs hierarchical specification of hematopoietic lineages

The mechanism of lineage specification in multipotent stem cells has not been fully understood. We recently isolated progenitors with the eosinophil, basophil, or mast cell lineage potential, all of which originate from granulocyte/ monocyte progenitors (GMPs). By using these prospectively purified progenitors, we show here that the expression timing of GATA-2 and CCAAT enhancer-binding protein alpha (C/EBP alpha) can differentially control their lineage commitment. The expression of GATA-2 instructed C/EBP alpha-expressing GMPs to commit exclusively into the eosinophil lineage, while it induced basophil and/or mast cell lineage commitment if C/EBP alpha was suppressed at the GMP stage. Furthermore, simply by switching the order of C/EBP alpha and GATA-2 transduction, even lymphoid-committed progenitors recaptured these developmental processes to be reprogrammed into each of these lineages. We propose that the order of expression of key transcription factors is critical for their interplay to selectively drive lineage specification programs, by which stem cells could generate multiple lineage cells in a hierarchical manner.