GATA1 is a master regulator of erythropoiesis, expression of which is regulated by multiple discrete cis-acting elements. In this study, we examine the activity of a promoter-proximal double GATA (dbGATA) motif, using a Gata1 bacterial artificial chromosome (BAC)-transgenic green fluorescent protein (GFP) reporter (G1BAC-GFP) mouse system. Deletion of the dbGATA motif led to significant reductions in GFP expression in hematopoietic progenitors, while GFP expression was maintained in erythroblasts. Consistently, in mice with a germ line deletion of the dbGATA motif (Gata1 ⌬dbGATA mice), GATA1 expression in progenitors was significantly decreased. The suppressed GATA1 expression was associated with a compensatory increase in GATA2 levels in progenitors. When we crossed Gata1 ⌬dbGATA mice with Gata2 hypomorphic mutant mice (Gata2 fGN/fGN mice), the Gata1 ⌬dbGATA ::Gata2 fGN/fGN compound mutant mice succumbed to a significant decrease in the progenitor population, whereas both groups of single mutant mice maintained progenitors and survived to adulthood, indicating the functional redundancy between GATA1 and GATA2 in progenitors. Meanwhile, the effects of the dbGATA site deletion on Gata1 expression were subtle in erythroblasts, which showed increased GATA1 binding and enhanced accumulation of active histone marks around the 1st-intron GATA motif of the ⌬dbGATA locus. These results thus reveal a novel role of the dbGATA motif in the maintenance of Gata1 expression in hematopoietic progenitors and a functional compensation between the dbGATA site and the 1st-intron GATA motif in erythroblasts.
GATA1 is a member of the GATA zinc finger transcription factor family and plays a central role in erythropoiesis (1-3). GATA1 expression starts at common myeloid progenitor (CMP) stage, and the expression level increases when erythroid lineage cells differentiate into the proerythroblast stage (4, 5). From the proerythroblast stage onward, the GATA1 expression level decreases as red blood cells mature. This dynamic change in GATA1 expression is essential for erythropoiesis, since constitutive expression of GATA1 at a high level under the regulation of the human -globin gene in transgenic mice is lethal due to defective erythroid cell maturation (6). A series of studies have revealed that the Gata1 gene is regulated through the activity of multiple cisregulatory elements (1-3). However, the precise contribution of each cis-element to Gata1 expression in specific hematopoietic lineages and differentiation stages has not been fully understood.The murine Gata1 locus is composed of two alternative noncoding first exons, IT and IE, and five coding exons, II to VI. The distal IT promoter specifies Gata1 gene expression in testicular Sertoli cells, whereas the proximal IE promoter directs gene expression in hematopoietic lineage cells (7). We have demonstrated by transgenic reporter mouse assays that an 8-kb region covering from 3.9 kb upstream of the IE exon to the 2nd exon contains sufficient regulatory information to direct Gata1 g...