Friend of GATA-1 (FOG-1) is a binding partner of GATA-1, a zinc finger transcription factor with crucial roles in erythroid, megakaryocytic, and mast-cell differentiation. FOG-1 is indispensable for the function of GATA-1 during erythro/megakaryopoiesis, but FOG-1 is not expressed in mast cells. Here, we analyzed the role of FOG-1 in mast-cell differentiation using a combined experimental system with conditional gene expression and in vitro hematopoietic induction of mouse embryonic stem cells. Expression of FOG-1 during the progenitor period inhibited the differentiation of mast cells and enhanced the differentiation of neutrophils. Analysis using a mutant of PU.1, a transcription factor that positively or negatively cooperates with GATA-1, revealed that this lineage skewing was caused by disrupted binding between GATA-1 and PU.1, which is a prerequisite for mast-cell differentiation. However, FOG-1 expression in mature mast cells brought approximately a reversible loss of the mast-cell phenotype. In contrast to the lineage skewing, the loss of the mast-cell phenotype was caused by down-regulation of MITF, a basic helix-loop-helix transcription factor required for mast-cell differentiation and maturation. These results indicate that FOG-1 inhibits mast-cell differentiation in a differentiation stage-dependent manner, and its effects are produced via different molecular mechanisms.
IntroductionIn hematopoiesis, more than 10 lineages of mature blood cells are derived from a single hematopoietic stem cell. 1 This process is tightly regulated by extrinsic environmental cues and an intrinsic genetic program. Multipotent hematopoietic cells gradually lose their differentiation ability, giving rise to lineage-restricted hematopoietic progenitors. Once matured, each type of blood cell expresses a set of lineage-specific genes that supports its physiologic functions. Several lineage-specific transcription factors have been identified that control lineage-specific gene expression, and recent studies have demonstrated that these transcription factors cooperate with other transcription factors and cofactors. Moreover, these lineage-specific transcription factors display a variety of biologic functions in a cellular context-dependent manner.The GATA family is the most extensively studied group of hematopoietic transcription factors. All GATA factors recognize a specific DNA sequence known as a GATA box [(A/T)GATA(A/ G)] 2 using the C-finger domain in one of their 2 zinc fingers (N-and C-fingers). GATA-1, a founding member of the GATA family, is highly expressed in erythroid cells, megakaryocytes, mast cells, and eosinophils. 3,4 Gene targeting analyses have shown that GATA-1 is essential for terminal differentiation in erythropoiesis and megakaryopoiesis. [5][6][7][8] Deletion of the upstream regulatory elements in GATA-1 gene leads to reduced GATA-1 expression (GATA-1 low ), 9 indicating that the gene plays a pivotal role in mast-cell differentiation. In GATA-1 low mice, morphologically abnormal mast cells were observed i...