Analysis of TIF1gamma Conditional Knockout Establishes a Requirement for the Differentiation of Multiple Hematopoietic Lineages

Abstract 744

Vertebrate hematopoiesis is regulated by cell-specific transcription factors that couple to RNA polymerase-associated basal machinery. Mutation of the chromatin factor TIF1gamma (TIF1g) gene in the zebrafish moonshine mutant causes a profound decrease in expression of most erythroid genes. Our previous work in the zebrafish system established an essential role of TIF1g in transcription elongation by coupling the SCL transcription factor complex to the transcription elongation machinery, and erythroid-specific transcription is paused in moonshine mutant (Bai et al., Cell 2010). Here we examined the role of TIF1g in murine hematopoiesis by studying conditional knockout (KO) models. Deletion of TIF1g was either induced in adult mice by Mx-Cre or during mouse development by vav-Cre. Both Cre systems induce excision at the HSC level and in all hematopoietic lineages. We observed the same trend of multi-lineage defects in both Cre lines, including decreased erythropoiesis in the bone marrow, loss of mature B cells and expansion of granulocytes. Bone marrow analysis of TIF1g-deleted mice revealed a block in erythroid differentiation starting as early as the BFU-E stage, consistent with the erythroid defect in the zebrafish moonshine mutant, confirming an evolutionarily conserved role for TIF1g in vertebrate erythropoiesis. A subset of the vav-Cre induced KO mice developed a MPD (myeloproliferative disease)-like phenotype at 1–3 months after birth, including a dramatic increase of dysplastic granulocytes in the peripheral blood and massive extramedullary hematopoiesis in spleen and liver, suggesting a requirement for TIF1g in myeloid differentiation and proliferation. Consistent with the KO mouse phenotype, we observed an increase of definitive myelopoiesis in the zebrafish TIF1g mutant. In addition, mature B cells were absent in KO mice, and this loss was observed as early as the pre-B stage, suggesting a defect occurring at the pro-B to pre-B transition. At the progenitor level, we observed an increase of GMP, MPP, and HSCs in bone marrow, suggesting that TIF1g may be required to control proliferation at the stem/progenitor cell stage or in the committed myeloid lineage. Our study reveals an essential function of TIF1g in regulating the differentiation and proliferation of multiple hematopoietic lineages.

Reference

Bai X, Kim J, Yang Z, Jurynec M, Akie T, et al. (2010) TIF1gamma controls erythroid cell fate by regulating transcription elongation. Cell. 142:133-43.