Commitment of multipotential hematopoietic progenitors to unique cell fates is determined by the induction and interplay of specific nuclear factors that reinforce unilineage transcriptional programs. Previously, we reported that loss of transcription factor GATA-1 promotes the expansion of bipotential megakaryocyte erythroid progenitors (MEPs) from embryonic stem cell or fetal liver derived hematopoietic progenitors. These mutant cells, termed G1ME (for Gata-1− Megakaryocyte-Erythroid), proliferate in culture and differentiate into committed megakaryocytes and erythroblasts when GATA-1 activity is restored. To evaluate gene regulation at the MEP stage of hematopoiesis, we performed microarray analysis of G1ME cells before and after GATA-1-induced differentiation. Expression of GATA-1 in G1ME cells induced numerous erythroid and megakaryocytic target genes. In addition, undifferentiated G1ME cells expressed numerous granulocyte and macrophage genes, suggesting that loss of GATA-1 derepresses a myeloid program in MEPs. Myeloid genes were rapidly inhibited upon expression of GATA-1. In particular, mRNA encoding the myeloid transcription factor PU.1 and more than thirty of its downstream targets were repressed by GATA-1. Chromatin immunoprecipitation (ChIP) showed that GATA-1 bound directly to the PU.1 gene (Sfpi1) at the promoter and at a −18kb upstream region coincident with repression. At the same regions, GATA-1 triggered release of both GATA-2, a related transcription factor expressed in multipotential progenitors, and PU.1, a positive autoregulator of its own gene. While GATA-1 is known to inhibit PU.1 functions through direct protein interactions, this work shows that antagonism also occurs at the level of Sfpi1 gene transcription. Together, our findings indicate that GATA-1 not only positively regulates an erythro-megakaryocytic program of gene expression, but also actively restrains myelopoiesis by inhibiting Sfpi1 expression directly. More generally, our work reveals a new mechanism through which cross-antagonism between transcription factors reinforces lineage commitment decisions in hematopoiesis.
Disclosure: No relevant conflicts of interest to declare.