Critical role of P1-Runx1 in mouse basophil development

Abstract

IntroductionBasophils are the least prevalent of the granulocytes, generally representing less than 1% of leukocytes in the peripheral blood. Basophil studies have been hampered by the rarity of these cells and, until recently, the lack of tools such as basophil-deficient mice with which to assess their roles in vivo. However, recent studies have unveiled evidence for several previously unrecognized roles for basophils that are distinct from those of mast cells. [1][2][3][4][5][6][7][8][9][10][11] In addition to hampering investigations of basophil function, the small numbers of basophils and the paucity of tools for their analysis have made studies of basophil development challenging and therefore there have been few studies of this process. Arinobu et al showed that basophil lineage-restricted progenitors (BaPs) are identifiable in the BM and that the transcription factor CCAAT/ enhancer-binding protein-␣ (C/EBP␣) is important for the fate decision to develop into terminally differentiated basophils. 12 Ohmori et al reported that the IL-3-STAT5 axis is important for differentiating granulocyte-monocyte progenitors to BaPs, 13 and Siracusa et al showed that thymic stromal lymphopoietin (TSLP) can facilitate the development of BaPs into mature basophils. 8 Despite such progress, many of the details of the basophil differentiation pathway remain to be determined. For example, it is known that IL-3-deficient, 8,14,15 TSLP receptor (TSLPR)-deficient, 8 and IL-3/TSLPR double-deficient 8 mice have normal baseline numbers of basophils, indicating that other factors are more important in maintaining basophil levels at baseline. Moreover, C/EBP␣-deficient mice die within 8 hours of birth 16 and STAT5-deficient mice die in utero, 17 limiting the ability to use these animals to evaluate factors that might regulate basophil development at baseline in adult mice in vivo.Runt-related transcription factor (Runx) proteins are a family of transcription factors 18,19 that have crucial roles during the development of many tissues and the immune system. Each of the 3 kinds of Runx proteins, Runx1, Runx2, and Runx3,19,20 has distinct roles in development, with Runx1 being required for hematopoiesis, 18 Runx2 for osteogenesis, 21,22 and Runx3 for neurogenesis, thymopoiesis, and the control of gastric epithelial-cell proliferation. [23][24][25] Although a constitutive deficiency in Runx1 is embryonically lethal, studies of conditional Runx1-knockout mice have indicated that Runx1 can regulate the differentiation of hematopoietic stem cells (HSCs), B lymphocytes, natural killer T (NKT) cells, and T lymphocytes. 18,[26][27][28][29][30] Mx-Cre Runx1-knockout mice, which have an inducible Runx1 inactivation system, exhibit normal numbers of HSCs, a normal myeloid-cell (neutrophil) compartment, a severe reduction in megakaryocyte differentiation and platelet formation, and defects in B and T lymphocytes. 31 All 3 Runx genes can be transcribed from the distal (P1) or proximal (P2) promoters, 32 and P1-and P2-derived Runx1 variants differ i...

Comprehensive population-based genome sequencing provides insight into hematopoietic regulatory mechanisms

“…Functional assays revealed that the causal variant altered enhancer activity and resulted in decreased CEBPA expression, which therefore helps drive the lineage choice between basophils and mast cells. Whether this lineage choice happens at the BMCP or a different myeloid progenitor stage is currently not resolved, and because our GWAS study did not measure mast cells in nonhematopoietic tissues, our findings cannot directly address this issue (71,72). In the region of another master TF, GATA2, our study identified a basophil and eosinophil count-associated variant within a similar CMP-restricted enhancer associated with GATA2 expression.…”

Concordant mast cell and basophil production by individual hematopoietic blast colony-forming cells

“…The present data may provide a clue to explain, in part, the fate of basophils by documenting that at least some basophils can mature to, or generate, mast cells. However, as indicated by the P1 Runx-1-deficient mice where mast cell numbers are normal but basophils are few (21), not all mast cells need to have basophil precursors. Indeed, the present data showed that many blast colony-forming cells can produce mast cells without accompanying basophils.…”

“…Basophils appear to have nonredundant functions in vivo (17)(18)(19), but common progenitor cells for basophils and mast cells have been described (20). However, in P1 runt-related transcription factor-1 (Runx1)-deficient mice, basophils are severely depleted, but mast cell numbers are normal (21). In the present experiments, the development of basophils from blast colony-forming cells was also monitored to clarify their relationship to mast cells.…”

GATA-1 regulates the generation and function of basophils

“…The ordered expression of two transcription factors, GATA-2 and C/EBPα, appears to regulate the commitment of progenitor cells into the basophil lineage (30,32). Of note, mice deficient in the distal promoter-derived Runt-related transcription factor 1 (P1-Runx1) show severe basophilopenia with no apparent anomaly of mast cell, neutrophils, or eosinophils (33), indicating the requirement of P1-Runx1 for the later stage of basophil development. Recent studies demonstrated that basophils express GATA-1 (30,32,34), but its functional significance remains to be determined.…”