Transcriptional Signaling Centers Regulate Erythroid Gene Expression and are Disrupted in Common Variations of Human Red Blood Cell Traits

Hematopoietic progenitors respond to developmental and environmental cues to differentiate. The stage-specific steps of differentiation are stereotypic for each cell lineage, and are controlled by transcription. Here we investigate how differential genomic binding of signal-responsive and lineage-restricted transcription factors can specify subsequent stages of erythropoiesis. Using a human erythroid differentiation system, we extensively characterized the co-operation of the BMP signaling transcription factor SMAD1 with the erythroid transcription factors GATA2 and GATA1 in a detailed time-course. BMP signaling enhances erythroid differentiation. SMAD1 is co-recruited with GATA factors at stage-specific genes that are required to have high expression in each stage. Additionally, we observed SMAD1-GATA co-enriched regions are within super-enhancers and span accessible chromatin. Co-bound regions harbor cell-type specific transcription factor motifs that change during commitment, in contrast to GATA-alone regions. Our studies demonstrate that signal-responsive factors together with lineage regulators mark genomic “hotspots” that function to regulate stage-specific gene expression. ChIP-Seq for H3K27ac, GATA1, GATA2, and SMAD1, after a 2hr pulse of hrBMP, on progenitor and differentiating human CD34+ cells towards erythrocytes.