Graded Levels of GATA-1 Expression Modulate Survival, Proliferation, and Differentiation of Erythroid Progenitors

Abstract

Transcription factor GATA-1 plays an important role in gene regulation during the development of erythroid cells. Several reports suggest that GATA-1 plays multiple roles in survival, proliferation, and differentiation of erythroid cells. However, little is known about the relationship between the level of GATA-1 expression and its nature of multifunction to affect erythroid cell fate. To address this issue, we developed in vitro embryonic stem (ES) culture system by using OP9 stromal cells (OP9/ES cell co-culture system), and cultured the mutant (GATA-1.05 and GATA-1-null) and wild type (WT) ES cells, respectively. By using this OP9/ES cell co-culture system, primitive and definitive erythroid cells were developed individually, and we examined how expression level of GATA-1 affects the development of erythroid cells. GATA-1.05 ES-derived definitive erythroid cells were immature with the appearance of proerythroblasts, and highly proliferated, compared with WT and GATA-1-null ES-derived erythroid cells. Extensive studies of cell cycle kinetics revealed that the GATA-1.05 proerythroblasts accumulated in S phase and expressed lower levels of p16INK4A than WT ES cell-derived proerythroblasts. We concluded that GATA-1 must achieve a critical threshold activity to achieve selective activation of specific target genes, thereby influencing the developmental decision of an erythroid progenitor cell to undergo apoptosis, proliferation, or terminal differentiation.

Pluripotent stem cells reveal erythroid-specific activities of the GATA1 N-terminus

“…Thus, it is possible that GATA1s functions normally, but is expressed at insufficient levels for optimal erythropoiesis. Supporting this, mutant mice expressing modestly reduced levels of WT GATA1 protein are anemic (25,26), and transgenic rescue with high levels of GATA1s restores erythropoiesis in a different strain of Gata1-deficient mice (9). Moreover, we show that enforced expression of ectopic GATA1s enhances erythropoiesis in iPSC-derived progenitors from patients with GATA1s mutations (Figure 3).…”

“…GATA1 regulates hematopoietic cell fates by activating lineagespecific genes and repressing those of alternate cell types (31). Previous loss-of-function and overexpression studies demonstrated that GATA1 stimulates differentiation of multipotent progenitors toward erythroid fate (44)(45)(46)(47)(48) and also acts as a survival/maturation factor for committed erythroblasts (26,49). The reduced erythropoietic activities of GATA1s demonstrated in the current study could occur through either or both mechanisms.…”

“…In mice, mutations that decrease the expression of normal GATA1 protein impair erythropoiesis (25,26). Thus, diminished levels of overall GATA1 expression may explain the wald-Giemsa staining revealed numerous late-stage erythroblasts in day-20 EB cultures from WT GATA1 iPSCs (T21 or euploid), but not from GATA1s iPSCs ( Figure 1E).…”

“…Both WT GATA1 and GATA1s produce dosage-dependent effects (9,25,26). GATA1s mutations typically reduce overall GATA1 protein output.…”

Loss of the Gata1 Gene IE Exon Leads to Variant Transcript Expression and the Production of a GATA1 Protein Lacking the N-terminal Domain

“…A complete loss of GATA1 provokes apoptotic cell death and differentiation arrest of erythroid progenitors. By contrast, Gata1 gene expression at 5% of the endogenous level protects erythroid cells from apoptosis, but does not promote erythroid differentiation (19,24). Two preceding conditional knock-out experiments further revealed that ablation of the entire Gata1 gene in adulthood either blocks differentiation at the proerythroblast stage or leads to a phenotype resembling human pure red cell aplasia (4).…”