Growth Factor Independence 1b (Gfi1b) Is Important for the Maturation of Erythroid Cells and the Regulation of Embryonic Globin Expression

Abstract

Growth factor independence 1b (GFI1B) is a DNA binding repressor of transcription with vital functions in hematopoiesis. Gfi1b-null embryos die at midgestation very likely due to defects in erythro- and megakaryopoiesis. To analyze the full functionality of Gfi1b, we used conditionally deficient mice that harbor floxed Gfi1b alleles and inducible (Mx-Cre, Cre-ERT) or erythroid specific (EpoR-Cre) Cre expressing transgenes. In contrast to the germline knockout, EpoR-Cre mediated erythroid specific ablation of Gfi1b allows full gestation, but causes perinatal lethality with very few mice surviving to adulthood. Both the embryonic deletion of Gfi1b by EpoR-Cre and the deletion in adult mice by Mx-Cre or Cre-ERT leads to reduced numbers of erythroid precursors, perturbed and delayed erythroid maturation, anemia and extramedullary erythropoiesis. Global expression analyses showed that the Hba-x, Hbb-bh1 and Hbb-y embryonic globin genes were upregulated in Gfi1b deficient TER119+ fetal liver cells over the gestation period from day 12.5–17.5 p.c. and an increased level of Hbb-bh1 and Hbb-y embryonic globin gene expression was even maintained in adult Gfi1b deficient mice. While the expression of Bcl11a, a regulator of embryonic globin expression was not affected by Gfi1b deficiency, the expression of Gata1 was reduced and the expression of Sox6, also involved in globin switch, was almost entirely lost when Gfi1b was absent. These findings establish Gfi1b as a regulator of embryonic globin expression and embryonic and adult erythroid maturation.

From cytopenia to leukemia: the role of Gfi1 and Gfi1b in blood formation

“…[52][53][54] Similar analyses with murine Gfi1b-deficient HSCs, megakaryocytes, or erythroid cells demonstrated that Gfi1b helps to establish gene expression programs necessary for the development of both erythroid and megakaryocytic lineages 29,32,55 and confirms the complementary roles of Gfi1 and Gfi1b in hematopoiesis already suspected by their differential, cell type-specific expression pattern.…”

“…The constitutive genetic ablation of Gfi1b in mice arrests embryonic development at approximately embryonic day 15.5. Two independent studies agree that the embryonic lethality in Gfi1b knockout mice is most likely because of defective erythropoiesis 32,67 and also suggest that Gfi1b is important for megakaryopoiesis and platelet formation. In addition, adult conditional knockout mice carrying floxed alleles and transgenes for doxycyclineor pIpC-inducible Cre expression reach similar conclusions about the effect of Gf11b deletion for erythropoiesis and megakaryopoiesis, 29,55 because the loss of Gfi1b in both models was characterized by a failure to produce Gfi1b-deficient red blood cells and platelets.…”

Combined alpha-delta platelet storage pool deficiency is associated with mutations in GFI1B

“…The conditional absence of Gfi1b in mice leads to arrest at the promegakaryocyte stage, after endomitosis is completed but before the maturation of the cytoplasm [30]. In erythrocytes, the conditional inactivation of Gfi1b leads to impaired differentiation of pro-erythroblasts to mature erythrocytes [31]. A long isoform of GFI1B that contains exon 5 is essential for megakaryopoiesis, while a short isoform lacking exon 5 is essential for its erythropoietic role [14].…”

Diverse noncoding mutations contribute to deregulation of cis-regulatory landscape in pediatric cancers

“…The GATA2 binding sites in the enhancer were disrupted and GFI1B expression decreased correspondingly ( Figure 3D, E). Growth factor independence 1b (GFI1B) encodes a key transcription factor regulating dormancy and proliferation of hematopoietic stem cells (HSCs) and the development of erythroid and megakaryocytic cells (31,32). Recent studies had revealed its critical role as a tumor suppressor in AML, as low GFI1B expression is associated with poor patient survival (33).…”