5-hydroxymethylcytosine poises expression of genes involved in hematopoietic differentiation

Epigenetic processes regulate hematopoietic stem cell homeostasis. The recent discovery of 5-hydroxymethylcytosine (5hmC) provides new insights into the epigenetic regulation of gene expression during development. We used reduced representation of 5-hydroxymethylcytosine profiling (RRHP) to characterize the genome-wide distribution of 5hmC in human CD34+ hematopoietic stem/progenitor cells, lymphocytes, monocytes and granulocytes. We show that 5hmC levels decrease during cell differentiation and that 5hmC is associated with H3K4me1 and H3K27ac histone modifications, indicative of active enhancers. In CD34+ cells, the presence of 5hmC at presumed active enhancers correlates with increased binding of RUNX1 and FLI1, two transcription factors essential for hematopoiesis. Moreover, in progenitor cells, 5hmC poises the expression of transcription factors regulating hematopoietic lineage commitment, such as RUNX1, FOXO1 and C/EBP-alpha. Our study provides the first comprehensive genome-wide overview of 5hmC distribution in human hematopoietic cells and of its potential role in transcriptional network regulation during hematopoiesis. Overall design: RRHP: profiling of 5-hydroxymethylcytosine and RNA-seq in human blood cells