Growth Factor Independence 1b (Gfi1b) Is Required for the Regulation of Fetal Globin Genes in Both Fetal and Adult Erythroid Cells
Bibliographic record
Abstract
Abstract Abstract 350 Gfi1b is hematopoietic transcription factor most highly expressed in hematopoietic stem cells, megakaryocyte-erythroid precursors, megakaryocytes and throughout erythroid development. Gfi1b deficiency is lethal in mice around 13.5 dpc caused by a failure to produce functional erythrocytes, megakaryocytes and platelets, which causes severe hemorrhaging. Since this lethality has hampered further analysis of the function of Gfi1b, we used Cre-recombinase inducible conditional Gfi1b knock-out mice (Gfi1bfl/fl). The pIpC induced knock-out of Gfi1b in Gfi1bfl/flMxCre mice leads to a pronounced drop in peripheral blood platelet numbers and induces a strong extramedullary erythropoiesis in the spleen. We sorted Ter119+ bone marrow cells from wt and pIpC induced Gfi1bfl/flMxCre mice for a genome wide expression array analysis and found a significant increase in the expression levels of platelet/coagulation related genes such as PF4, vWF, F2r or Ppbp as well as of the fetal globin genes Hba-x, Hbb-ey and Hbb-ßh1, suggesting that Gfi1 regulates globin gene expression or globin switching. It remained unclear whether the disturbed erythropoiesis in Gfi1b deficient mice was caused by a bone marrow failure, or was a reaction to the anemia caused by internal bleedings as a result of low platelet counts. To clarify this and to avoid deletion of Gfi1b in megakaryocytes, we crossed Gfi1bfl/fl mice with EpoR-EGFP-Cre mice allowing a Gfi1b deletion specifically in erythroid cells at the pro-erythroblast stage. Gfi1bfl/flEpoR-EGFP-Cre embryos were paler than wt littermates, but in contrary to complete knock-outs showed no internal bleedings and had normal platelet counts. In addition, EpoR-EGFP-Cre embryos showed a mild block in terminal erythroid differentiation and a pronounced hyper-proliferation at the Ter119-,CD71+, cKit+ proerythroblast stage where Cre expression is activated. Gfi1bfl/flEpoR-Cre cells showed a strong increase of fetal Hbb-ßH1 globin gene expression and a pronounced decrease of the expression of the adult globin genes Hba, Hbb, as well as of Gata1, Foxo3a and Nfe2l2 but not Gata2. Gene expression-array analysis of fetal liver cells from wt and Gfi1bfl/flEpoR-Cre embryos from day 14.5 dpc showed that besides fetal globin genes, many genes where up-regulated that normally decrease in expression during the development between the embryonic stages 11.5 dpc to 14.5 dpc. These findings confirm that Gfi1b is required for the regulation of globin gene expression during or at the transition from embryonic/fetal to adult stages. Interestingly, Gfi1bfl/flEpoR-Cre mice were viable very likely because these animals have normal platelet counts and do not suffer from hemorrhaging like constitutive Gfi1b deficient mice. However, this also suggested that the block in erythroid development is tolerable, or that it can be overcome during maturation of the embryo. Q-PCR analysis on mRNA from sorted erythroid cells from wt and adult Gfi1bfl/flEpoR-Cre mice showed a highly increased expression of the fetal globin genes Hbb-ßh1, Hbb-ey and Hba-x but only a slight decrease of Gata1 expression, a mild increase in Nfe2l2 expression and no significant expression of Gata2 compared to age matched wild type controls. A recently published study of genome wide in vivo DNA binding of ten major hematopoietic transcription factors (Wilson et al., Cell Stem Cell, 2010) showed Gfi1b binding to hypersensitive site 2 in the globin locus control region (LCR) where also the Gfi1b interaction partner Gata1 and Nfe2 bind. From these data we conclude, that Gfi1b is required to regulate the expression of fetal globin genes during the switch from embryonic/fetal to adult stages and thereafter during adult globin expression and exerts this function by directly binding to regulatory sites in the globin locus. Since the re-expression of fetal globin genes in adult stages is a therapeutic approach for ß-thalassemia, the function of Gfi1b and its regulatory mechanisms could point to new therapeutic strategies for this disease. Disclosures: No relevant conflicts of interest to declare.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".