An NFIX-mediated regulatory network governs the balance of hematopoietic stem and progenitor cells during hematopoiesis.

The transcription factor (TF), nuclear factor I-X (NFIX), is a positive regulator of hematopoietic stem and progenitor cell (HSPC) transplantation. Nfix-deficient HSPC exhibit a severe loss of repopulating activity, increased apoptosis and a loss of colony forming potential. However, the underlying mechanism remains elusive. Here, we performed cellular indexing of transcriptomes and epitopes by high-throughput sequencing (CITE-seq) on Nfix-deficient HSPC and observed loss of long-term hematopoietic stem cells (LT-HSC) and an accumulation of megakaryocyte and myelo-erythroid progenitors. The genome-wide binding profile of NFIX in primitive murine hematopoietic cells revealed its co-localization with other hematopoietic TFs such as PU.1. We confirmed the physical interaction between NFIX and PU.1 and demonstrated that the two TFs co-occupy super-enhancers and regulate genes implicated in cellular respiration and hematopoietic differentiation. Additionally, we provide evidence suggesting the absence of NFIX negatively affects PU.1 binding at some genomic loci. Our data support a model in which NFIX collaborates with PU.1 at super-enhancers to promote the differentiation and homeostatic balance of hematopoietic progenitors.