The EMT transcription factor Zeb1 is essential for HSPC differentiation that acts synergistically with Zeb2 in fine-tuning hematopoietic lineage fidelity

The Zeb2 transcription factor has been demonstrated to play important roles in hematopoiesis and leukemic transformation. Zeb1 is a close family member of Zeb2 but has remained more enigmatic concerning its roles in hematopoiesis. Here we show using conditional loss of function approaches and bone marrow reconstitution experiments that Zeb1 plays cell autonomous role in hematopoietic lineage differentiation, particularly as a positive regulator of monocyte development in addition to its previously reported important role in T-cell differentiation. Analysis of existing single cell RNAseq data of early hematopoiesis has revealed distinctive expression differences between Zeb1 and Zeb2 in HSPC differentiation with Zeb2 being more highly and broadly expressed that Zeb1 except at a key transition point (ST-HSC towards MPP1) whereby Zeb1 appears to be the dominantly expressed family member. Inducible deletion of both Zeb1 and Zeb2 using a tamoxifen inducible Cre-mediated approach leads to acute bone marrow failure at this transition point with increased long-term and short-term hematopoietic stem cell numbers and an accompanying decrease in all hematopoietic lineage differentiation. Bioinformatics analysis of RNAseq data has revealed that Zeb2 acts predominantly as a transcriptional repressor involved in restraining mature hematopoietic lineage gene expression programs from being expressed too early in hematopoietic stem and progenitor cells (HSPCs). Zeb1 appears to fine tune this repressive role during hematopoiesis to ensure hematopoietic lineage fidelity. Analysis of ROSA26 locus based transgenic models has revealed that Zeb1 as well as Zeb2 overexpression within the hematopoietic system can drive extramedullary hematopoiesis/splenomegaly and enhanced monocyte development. Finally, deletion of Zeb2 alone or Zeb1/2 together was found to enhance survival in secondary MLL-AF9 AML models attesting to the oncogenic role of Zeb1/2 in AML.