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Transcription factor GATA-1 is essential for the development of the erythroid lineage. To ascertain whether strict control of GATA-1 expression level is necessary for achieving proper erythropoiesis, we established transgenic mouse lines expressing green fluorescent protein (GFP) under the control of the GATA-1 gene hematopoietic regulatory domain. We examined the GATA-1 expression level by exploiting the transgenic mice and found 2 GFP-positive hematopoietic progenitor fractions in the bone marrow. One is the GFP high fraction containing mainly CFU-E and proerythroblasts, which coexpress transferrin receptor, while the other is the GFP low /transferrin receptor-negative fraction containing BFU-E. Since the intensity of green fluorescence correlates well with the expression level of GATA-1, these results indicate that GATA-1 is highly expressed in erythroid colony-forming unit (CFU-E) but low in erythroid burstforming unit (BFU-E), suggesting that the incremental expression of GATA-1 is required for the formation of erythroid progenitors. We also examined GFP-positive fractions in the transgenic mouse spleen and fetal liver and identified fractions containing BFU-E and CFU-E, respectively. This study also presents an efficient method for enriching the CFU-E and BFU-E from mouse hematopoietic tissues. ( IntroductionPluripotent hematopoietic progenitors are committed to and differentiated along the erythroid lineage by the control of various cytokines, growth factors, and signals from the microenvironment. 1 In hematopoietic progenitors, these signals are transduced to transcription factors in the nucleus, and the progenitor cells differentiate and mature into erythrocytes by changing their gene expression profiles. 2 GATA-1 is a zinc-finger transcription factor, which plays a central role in erythropoiesis. GATA-1 binds to the GATA factor-binding motifs (T/A)GATA(A/G) that have been identified in the regulatory sequences of many genes expressed in erythroid and megakaryocytic cells. [3][4][5] Expression of GATA-1 is restricted to erythroid, megakaryocytic, eosinophilic, basophilic, and mast cells within the hematopoietic system. 6 The Sertoli cells in the testis also express GATA-1. 7 Mutations in the GATA-1 gene cause defects in erythropoiesis, platelet formation, mast cell maturation, and eosinophil development. [8][9][10][11][12][13][14] GATA-1-null mutant embryonic stem (ES) cells could not differentiate into mature erythrocytes due to the arrest of erythroid maturation at the proerythroblast stage. 15,16 The arrest provoked rapid apoptosis of the proerythroblasts. 17 We previously established GATA-1 gene knockdown ES cells, in which the GATA-1 expression level was reduced to approximately 5% of that in wild-type ES cells. 10,18 Proerythroblast-like cells derived from the GATA-1 knockdown ES cells have an ability to proliferate vigorously, but a GATA-1 level of 5% cannot sustain the gene expression required for maturation of proerythroblasts. 18 McDevitt et al also demonstrated that a 4-to 5-fold decrease in...

Although clinical and experimental studies have long suggested a role for the renin-angiotensin system (RAS) in the regulation of erythropoiesis, the molecular basis of this role has not been well understood. We report here that transgenic mice carrying both the human renin and human angiotensinogen genes displayed persistent erythrocytosis as well as hypertension. To identify the receptor molecule responsible for this phenotype, we introduced both transgenes into the AT1a receptor null background and found that the hematocrit level in the compound mice was restored to the normal level. Angiotensin II has been shown to influence erythropoiesis by two means, up-regulation of erythropoietin levels and direct stimulation of erythroid progenitor cells. Thus, we conducted bone marrow transplantation experiments and clarified that AT1a receptors on bone marrow-derived cells were dispensable for RAS-dependent erythrocytosis. Plasma erythropoietin levels and kidney erythropoietin mRNA expression in the double transgenic mice were significantly increased compared with those of the wild-type control, while the elevated plasma erythropoietin levels were significantly attenuated in the compound mice. These results provide clear genetic evidence that activated RAS enhances erythropoiesis through the AT1a receptor of kidney cells and that this effect is mediated by the elevation of plasma erythropoietin levels in vivo.